JP2005080491A - Power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply device that performs a stable noninstantaneous interruption power supply change-over and achieves the reduction in power loss during a steady-state operation. <P>SOLUTION: A first back-flow prevention switch 1b has a function to prevent the back-flow of electric current from a second power supply V2 to a first power supply V1. A first output interrupting switch 1a has a function to interrupt the power supply feed from the first power supply V1 when the second power supply V2 is used. A second back-flow prevention switch 1c has a function to prevent the back-flow of electric current from the first power supply V1 to the second power supply V2. A second output interrupting switch 1d has a function to interrupt the power supply feed from the second power supply V2, when the first power supply V1 is used. A first voltage sensing part 13-1 senses the voltages of the first power supply V1. A second voltage sensing part 13-2 senses the voltages of the second power supply V2. A change-over control part 14 performs ON/OFF change-over control of a first switch part 11 and a second switch part 12, based on the sensed results. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power supply device, and more particularly to a power supply device that can be used in combination with a plurality of power supplies.

  With the progress of multimedia in recent years, functions of various terminal devices for multimedia such as the Internet have been advanced in companies and general households. In particular, portable communication devices such as mobile phones and laptop computers that allow users to connect to a network at any time are becoming increasingly popular.

  Under such circumstances, stable power supply to mobile communication devices is indispensable, and demand for highly reliable power supply devices is increasing. Since portable communication devices can usually be used in combination with a battery and an AC adapter (a device that converts household 100V AC into low-voltage DC), power is supplied from the battery to the AC adapter or from the AC adapter to the battery. Switching is performed smoothly without instantaneous interruption (non-instantaneous power supply switching), and small power loss during steady operation is a major point in power supply unit development in portable communication devices.

  FIG. 26 is a diagram showing a configuration of a conventional uninterruptible power supply. The power supply device 200 includes a battery V1, an AC adapter V2, and diodes D1 and D2, and supplies power to the load 201. In addition, a smoothing input capacitor C0 is disposed in the load 201 in order to supply a DC voltage with less pulsation.

  Regarding the connection relationship of each element, the positive side of the battery V1 and the anode of the diode D1 are connected, and the cathode of the diode D1, one end of the capacitor C0, the Vin terminal of the load 201, and the cathode of the diode D2 are connected. The other end of the capacitor C0 and the GND terminal of the load 201 are connected to GND. The + side of the AC adapter V2 connected to the AC source is connected to the cathode of the diode D2. The negative side of battery V1 and AC adapter V2 is connected to GND.

  In the power supply device 200, the power supply line from the battery V1 and the power supply line from the AC adapter V2 are connected by the cathode common of the diodes D1 and D2. Thereby, even if the power supply of either the battery V1 or the AC adapter V2 is stopped, the power is supplied from one of the sides during operation, so that there is no instantaneous interruption.

  Further, in a redundant configuration using diodes such as the power supply device 200, the power supply with the higher voltage is prioritized and the power is supplied to the load 201. That is, when power can be supplied from both the battery V1 and the AC adapter V2, if (voltage of the battery V1) <(voltage of the AC adapter V2), the voltage from the AC adapter V2 is preferentially applied to the load 201. Will be.

  FIG. 27 is a diagram showing a configuration of a conventional uninterruptible power supply. The power supply device 210 includes a battery V1, an AC adapter V2, and switches sw1 and sw2, and supplies power to the load 201. As for the connection relationship of each element, the positive side of the battery V1 and one end of the switch sw1 are connected, and the other end of the switch sw1 is connected to one end of the switch sw2, one end of the capacitor C0, and the Vin terminal of the load 201. The other end of the capacitor C0 and the GND terminal of the load 201 are connected to GND. The + side of the AC adapter V2 connected to the AC source is connected to the other end of the switch sw2. The negative side of battery V1 and AC adapter V2 is connected to GND.

  When the power supply 210 supplies power from the battery V1 to the load 201, the switch sw1 is turned on and the switch sw2 is turned off. When power is supplied from the AC adapter V2 to the load 201, the switch sw1 is turned off and the switch sw2 is turned on. Is turned on.

  However, if both of the switches sw1 and sw2 are turned on during switching, the current Ibat from the battery V1 flows to the AC adapter V2 side, and the current Iadp from the AC adapter V2 flows to the battery V1. Since it flows backward, it is controlled not to turn on at the same time.

  At this time, when the power supply is switched from the battery V1 to the AC adapter V2 or from the AC adapter V2 to the battery V1, there is a slight time zone during which both the switches sw1 and sw2 are turned off. During this time, the capacitor C0 is charged. Since the charging voltage is applied to the load 201, an instantaneous interruption is prevented.

On the other hand, as a conventional technology for an uninterruptible power supply, when a battery is used, the backflow prevention diode is short-circuited, and the transistor connected in parallel to the backflow prevention diode is turned off. When the AC adapter is used, the backflow prevention diode functions. Thus, a technique for supplying power to a load has been proposed (for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-332113 (paragraph numbers [0014] to [0026], FIG. 1)

  In the power supply device 200 of FIG. 26 described above, there is no instantaneous interruption when switching the power supply, but power loss occurs due to a forward voltage drop of the diode during steady operation. Here, when the forward voltage drop of the diodes D1 and D2 is Vf, the current from the battery V1 is Ibat, and the current from the AC adapter V2 is Iadp, the power loss Wloss (D1) by the diode D1 when the battery is used is The power loss Wloss (D2) by the diode D2 when the AC adapter is used is calculated by the formula (1a), and is calculated by the formula (1b).

  Since the forward voltage drop Vf is normally about 0.5 V, as can be seen from the equations (1a) and (1b), if the necessary current (load current) for the load 201 increases, it is proportional to the current. As a result, the loss increases, and when the load current increases, the diodes D1 and D2 generate heat.

  On the other hand, in the case where FETs (Field Effect Transistors) are used for the switches sw1 and sw2 with respect to the power supply device 210 of FIG. 27, the power loss during the steady operation is the conduction loss of the FET. Here, assuming that the resistance value between the drain and the source when the FET is turned on is Rds (on), the conduction loss Wloss (sw1) when the switch sw1 is turned on is calculated by the following equation (2a), and the switch sw2 The conduction loss Wloss (sw2) at the time of ON is calculated by the following equation (2b).

  Since Rds (on) has a very small resistance value, the loss is considerably smaller than the power loss due to the diode. Therefore, the power supply device 210 has an advantage that power loss is smaller than that of the power supply device 200. The power supply device 210 is provided with a guard time so that the battery V1 and the AC adapter V2 are not turned on at the same time when the power supply is switched, although power loss during steady operation is reduced.

  FIG. 28 shows the guard time. At the time of switching from the battery V1 to the AC adapter V2, the guard time Twg is set so that both are not turned on simultaneously. During the guard time Twg, power supply from the battery V1 or the AC adapter V2 to the load 201 is stopped. During this time, power is supplied from the capacitor C0 installed on the load side. In this case, if the load current I0 flowing through the load 201 is large, the load voltage V0 is greatly reduced, so that a capacitor having a large capacity is required for the capacitor C0.

  Here, when the guard time is Twg, the capacitance of the capacitor C0 attached to the load 201 is C, and the load current is I0 (constant current), the voltage Vdip that decreases during the instantaneous interruption is expressed by the following equation (3). Calculated. FIG. 29 shows a waveform of the drooping voltage Vdip1 generated during the guard time Twg1.

  As can be seen from equation (3), the voltage Vdip can be reduced by reducing the guard time Twg or increasing the capacitance C. However, when the capacitance of the capacitor C0 is increased, when the FET is turned on, a large inrush current (a charging current that instantaneously flows through the capacitor) flows, causing circuit damage or malfunction in the load 201, so that the inrush current can be reduced. It is necessary to provide an inrush current prevention circuit.

  FIG. 30 is a diagram showing a drooping voltage when an inrush current prevention circuit is provided. When an inrush current prevention circuit is provided, the peak value of the inrush current when the power is turned on is suppressed by the time constant of the inrush current prevention circuit, and the inrush current is reduced. However, a delay occurs until the FET is completely turned on. As a result, the guard time increases (Twg2> Twg1), and the voltage Vdip2 increases. As described above, it is difficult to find an optimal solution, and there is a problem that the power supply device 210 cannot always perform stable uninterruptible power switching.

  On the other hand, in the prior art (Japanese Patent Laid-Open No. 11-332113), since a backflow prevention diode is inserted in the output of the AC adapter V2, a loss due to the diode always occurs when the AC adapter is operated. In addition, the relay switch is used to cut off the battery power supply from the load, but because it uses large parts such as a relay switch, it can be applied to the power supply of mobile communication devices that require miniaturization. Has the disadvantage of being unsuitable.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a power supply apparatus that supplies power by performing stable uninterruptible power supply switching with low power loss during normal operation.

  In the present invention, in order to solve the above-mentioned problem, a power supply apparatus capable of operating in combination with a first power supply V1 and a second power supply V2 having an output voltage higher than that of the first power supply V1, as shown in FIG. 10, a first backflow prevention switch 1b that is installed on the load 2 side of the first power supply line and has a function of preventing a backflow of current from the second power supply V2 to the first power supply V1; And a first output cut-off switch 1a having a function of cutting off the power supply from the first power supply V1 when the second power supply V2 is used. A first switch unit 11 that feeds the power supply V1 to the load 2 and a function that is installed on the load 2 side of the second power supply line to prevent backflow of current from the first power supply V1 to the second power supply V2. A second backflow prevention switch 1c having a power supply for the second power supply line And a second output cut-off switch 1d having a function of cutting off the power supply from the second power supply V2 when the first power supply V1 is used, and the second power supply V2 to the load 2 The second switch unit 12 that supplies power, the first voltage detection unit 13-1 that detects the voltage of the first power source V1, and the second voltage detection unit 13-2 that detects the voltage of the second power source V2. And a switching control unit 14 for performing ON / OFF switching control of the first switch unit 11 and the second switch unit 12 based on the result of voltage detection. Is done.

  Here, the first backflow prevention switch 1b is installed on the load 2 side of the first power supply line, and has a function of preventing a backflow of current from the second power supply V2 to the first power supply V1. The first output cut-off switch 1a is installed on the power supply side of the first power supply line, and has a function of cutting off the power supply from the first power supply V1 when the second power supply V2 is used. The second backflow prevention switch 1c is installed on the load 2 side of the second power supply line, and has a function of preventing a backflow of current from the first power supply V1 to the second power supply V2. The second output cut-off switch 1d is installed on the power supply side of the second power supply line and has a function of cutting off the power supply from the second power supply V2 when the first power supply V1 is used. The first voltage detector 13-1 detects the voltage of the first power supply V1. The second voltage detector 13-2 detects the voltage of the second power supply V2. The switching control unit 14 performs ON / OFF switching control of the first switch unit 11 and the second switch unit 12 based on the result of voltage detection.

  The power supply apparatus of the present invention has a function of preventing a backflow of current from the second power supply to the first power supply and a function of cutting off the power supply from the first power supply when the second power supply is used. A second switch unit having a function of preventing a backflow of current from the first power source to the second power source and a function of shutting off the power supply from the second power source when the first power source is used. And a switch control for ON / OFF switching of the switch based on the result of voltage detection. This makes it possible to perform stable uninterruptible power supply switching.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a principle diagram of a power supply device. The power supply device 10 is a device that can be used in combination with the first power supply V1 and the second power supply V2 and supplies either one of the power supplies to the load 2. In the following description, it is assumed that the first power supply V1 is the battery V1 and the second power supply V2 is the AC adapter V2, and that (the voltage Vbat of the battery V1) <(the voltage Vadp of the AC adapter V2).

  The switch unit 11 (first switch unit) includes a backflow prevention switch 1b (first backflow prevention switch) and an output cutoff switch 1a (first output cutoff switch). The backflow prevention switch 1b is installed on the load 2 side of the power supply line of the battery V1, and has a function of preventing a backflow of current from the AC adapter V2 to the battery V1. The output cut-off switch 1a is installed on the power supply side of the power line of the battery V1, and has a function of cutting off the power supply from the battery V1 when the AC adapter V2 is used.

  The switch unit 12 (second switch unit) includes a backflow prevention switch 1c (second backflow prevention switch) and an output cutoff switch 1d (second output cutoff switch). The backflow prevention switch 1c is installed on the load 2 side of the power line of the AC adapter V2, and has a function of preventing a backflow of current from the battery V1 to the AC adapter V2. The output cut-off switch 1d is installed on the power supply side of the power line of the AC adapter V2, and has a function of cutting off the power supply from the AC adapter V2 when the battery V1 is used.

  The voltage detector 13-1 (first voltage detector) detects the voltage (start / stop voltage) of the battery V1. The voltage detector 13-2 (second voltage detector) detects the voltage (start / stop voltage) of the AC adapter V2. The switching control unit 14 performs ON / OFF switching control of the switch unit 11 and the switch unit 12 based on the result of voltage detection.

  Since FETs are used for the above switches, in the following description, the output cutoff switch 1a is called FET 1a, the backflow prevention switch 1b is FET1b, the backflow prevention switch 1c is FET1c, and the output cutoff switch 1d is FET1d.

  Next, the configuration of the power supply device 10 will be described. FIG. 2 is a diagram illustrating a configuration of the power supply device 10. As the FETs 1a to 1d, MOS (Metal Oxide Semiconductor) type P-channel FETs (FETs through which current flows when the gate is at a lower voltage than the source) are used. Further, parasitic diodes d1 to d4 that are inevitably formed in the structure of the IC exist in the FETs 1a to 1d (hereinafter, the parasitic diode is referred to as a body diode). The voltage detector 13-1 includes a comparator comp1 and a reference voltage source Vr1, and the voltage detector 13-2 includes a comparator comp2 and a reference voltage source Vr2.

  When the connection relation of each element is described, on the + side of the battery V1, the (+) input terminal of the comparator comp1, the source of the FET 1a, and the cathode of the body diode d1 are connected. The drain of the FET 1a is connected to the drain of the FET 1b, the anode of the body diode d1, and the anode of the body diode d2.

  The source of the FET 1b is connected to the source of the FET 1c, the cathode of the body diode d2, the cathode of the body diode d3, one end of the capacitor C0, and the Vin terminal of the load 2. The drain of the FET 1c is connected to the drain of the FET 1d, the anode of the body diode d3, and the anode of the body diode d4. The + side of the AC adapter V2 connected to the AC source is connected to the source of the FET 1d, the cathode of the body diode d4, and the (+) input terminal of the comparator comp2.

  The gate of the FET 1a is connected to the Va terminal of the switching control unit 14, the gate of the FET 1b is connected to the Vb terminal of the switching control unit 14, the gate of the FET 1c is connected to the Vc terminal of the switching control unit 14, and the FET 1d The gate is connected to the Vd terminal of the switching control unit 14. The Va terminal to Vd terminal are terminals for controlling ON / OFF of the FETs 1a to 1d by applying bias voltages to the respective gates of the FETs 1a to 1d.

  The output terminals of the comparators comp1 and comp2 are connected to the Vbaton terminal and the Vadpon terminal of the switching control unit 14, respectively. The Vbaton terminal is a terminal for detecting the voltage state of the battery V1, and the Vadpon terminal is a terminal for detecting the voltage state of the AC adapter V2.

  The (−) input terminal of the comparator comp1 is connected to the + side of the reference voltage source Vr1, and the (−) input terminal of the comparator comp2 is connected to the + side of the reference voltage source Vr2. The other end of the capacitor C0, the GND terminal of the load 2, the GND terminal of the switching control unit 14, the negative side of the battery V1, the negative side of the AC adapter V2, and the negative side of the reference voltage sources Vr1 and Vr2 are GND. Connect to.

  Here, the connection relationship of the FETs 1a to 1d is such that the body diode d1 of the FET 1a and the body diode d2 of the FET 1b are opposite to each other by connecting the drains of the FET 1a and the FET 1b as described above. The battery V1 is inserted in series on the power supply line. Similarly, by connecting the drains of the FET 1c and FET 1d, the body diode d3 of the FET 1c and the body diode d4 of the FET 1d are opposite to each other and inserted in series on the power supply line of the AC adapter V2. .

  Next, the voltage detection units 13-1 and 13-2 will be described. The voltage detection unit 13-1 detects a voltage from the battery V1 necessary for the operation of the load 2, and the voltage detection unit 13-2 detects a voltage from the AC adapter V2 required for the operation of the load 2.

  Here, in a portable communication device such as a notebook computer, when both a battery and an AC adapter are set, power is normally supplied from the AC adapter in order to reduce battery consumption as much as possible. The switching control unit 14 preferentially selects the AC adapter voltage Vadp.

  Further, assuming that the starting voltage from the reference voltage source Vr1 is Vref1 and the starting voltage from the reference voltage source Vr2 is Vref2, since (battery voltage Vbat) <(voltage Vadp of the AC adapter V2), Vref1 <Vref2 is set. The reference voltage sources Vr1 and Vr2 are provided in the voltage detection units 13-1 and 13-2.

  The comparator comp1 in the voltage detector 13-1 compares the starting voltage Vref1 and the battery voltage Vbat, and when Vref1 <Vbat, for example, sets the output signal to H level and outputs a Vbaton detection signal. The comparator comp2 in the voltage detection unit 13-2 compares the starting voltage Vref2 and the AC adapter voltage Vadp, and when Vref2 <Vadp, for example, sets the output signal to the H level and outputs a Vadpon detection signal. The switching control unit 14 performs switch switching control of the FETs 1 a to 1 d based on the Vbaton detection signal and the Vadpon detection signal, and supplies power to the load 2.

  FIG. 3 is a diagram showing the relationship between the starting voltage and the power supply voltage. The range of the battery voltage Vbat is 6.0v to 8.0V, the range of the AC adapter voltage Vadp is 8.5V to 9.5V, and the starting voltages Vref1 and Vref2 are set to voltage levels as shown in the figure.

When both the battery voltage Vbat and the AC adapter voltage Vadp do not exceed the starting voltages Vref1 and Vref2 (Vbat <Vref1, Vadp <Vref2), power is not supplied from either of them.
When only the AC adapter voltage Vadp exceeds the startup voltage Vref2 (Vbat <Vref1, Vadp> Vref1), the power supply source is the AC adapter V2, and when only the battery voltage Vbat exceeds the startup voltage Vref1 (Vbat > Vref1, Vadp <Vref1), and the power supply source is the battery V1.

  Further, when both the battery voltage Vbat and the AC adapter voltage Vadp exceed the starting voltages Vref1 and Vref2 (Vbat> Vref1, Vadp> Vref2), the power supply source is the AC adapter V2.

  Next, the operation of the FETs 1a to 1d when the power source is switched from the battery V1 to the AC adapter V2 will be described. In the following description, when the output cutoff FET is turned on, the output cutoff is released, and when the output cutoff FET is turned off, the output cutoff FET is turned off. Further, when the backflow prevention FET is turned on, the backflow prevention is canceled, and when it is turned off, the backflow prevention is prevented.

4-7 is a figure which shows operation | movement of FET1a-1d at the time of switching from the battery V1 to AC adapter V2. The operation modes S1 to S4 are sequentially shown in FIGS. In addition, illustration of the voltage detection parts 13-1 and 13-2 and the switching control part 14 is abbreviate | omitted in the figure.
[S1] Power supply from the battery V1 (load voltage V0 = battery voltage Vbat). At this time, the FET switching states are FET1a and 1b are ON, FET1c and 1d are OFF, and the power supply path is battery V1 → FET1a (ON) → FET1b (ON) → load 2.

  The battery current Ibat flows to the load 2 via the source of the FET 1a → the drain of the FET 1a → the drain of the FET 1b → the source of the FET 1b. Only a small amount of current flows in the direction, but in the case of an FET, current can flow from either the drain → source direction or the source → drain direction).

Further, since the FET 1c is OFF, the battery current Ibat is in the reverse direction with respect to the body diode d3 and does not flow backward to the AC adapter V2. Further, when the FET 1d is turned off, the body diode d4 blocks the output from the AC adapter V2.
[S2] When the AC adapter voltage Vadp is detected by the voltage detection unit 13-2, the switching control unit 14 immediately turns off the FET 1b to prepare for prevention of backflow to the battery V1 due to voltage application from the AC adapter V2. (The current to the battery V1 due to voltage application from the AC adapter V2 is in the opposite direction to the body diode d2). The power supply path is battery V1 → FET 1a (ON) → body diode d2 → load 2 (in this state, a voltage drop occurs by the forward voltage Vf of the body diode d2 of FET 1b).
[S3] The FET 1d is turned ON (the output cutoff on the AC adapter V2 side is released). At this time, the battery V1 and the AC adapter V2 are diode-redundantly connected to the body diodes d2 and d3. However, since the threshold voltage of the starting voltage of the AC adapter V2 is high, the power is supplied from the AC adapter V2. . The power supply path is AC adapter V2.fwdarw.FET1d (ON) .fwdarw.body diode d3.fwdarw.load 2. In this state, the voltage drops by the forward voltage Vf of the body diode d3 of FET1c, but there is no instantaneous interruption.
[S4] The FET 1c is turned on (preventing the backflow prevention from the battery V1 to the AC adapter V2), the Vf by the body diode d3 is removed, and the power supply state from the steady AC adapter V2 is established. The power supply path is AC adapter V 2 → FET 1 d (ON) → FET 1 c (ON) → load 2. The AC adapter current Iadp flows to the load 2 via the source of the FET 1d → the drain of the FET 1d → the drain of the FET 1c → the source of the FET 1c. Also, since Vbat <Vadp, Ibat does not flow.

FIG. 8 is a diagram showing a switching sequence from the battery V1 to the AC adapter V2. The switching state of the FET described above with reference to FIGS. 4 to 7 is shown in a time chart.
In the operation mode S1 → S2, when the AC adapter voltage Vadp exceeds the threshold value th, the FET 1b is immediately turned OFF. At this time, the load voltage V0 applied to the load 2 drops from the battery voltage Vbat by the forward voltage Vf of the body diode d2. However, even if the forward voltage Vf is reduced by about 0.5 V from the battery voltage Vbat, there is no hindrance to the operation of the load 2, so no instantaneous interruption occurs in the operation mode S1 → S2.

  On the other hand, in the operation mode S2 → S3, the FET 1d is turned on and power is supplied from the AC adapter V2. However, the power supply is reduced by the forward voltage Vf of the body diode d3 from the AC adapter voltage Vadp. In this case as well, even if the forward voltage Vf of about 0.5 V is lowered from the AC adapter voltage Vadp, there is no problem in the operation of the load 2, so that no instantaneous interruption occurs in the operation mode S2 → S3. In the operation mode S3 → S4, the FET 1c is turned on, the load voltage V0 becomes the AC adapter voltage Vadp, and the steady operation is performed by the AC adapter V2.

FIG. 9 is a diagram showing power loss in each operation mode. In the operation mode S1, the FET 1a and the FET 1b are turned on to supply the battery voltage Vbat. Therefore, the power loss Wloss1 in the time zone of the operation mode S1 is the sum of the conduction loss W _1a of the FET _1a and the conduction loss W _{1b of the} FET _1b. become _{(Wloss1 = W 1a + W 1b} ).

In the operation mode S2, since the FET 1a and the body diode d2 are turned on to supply the battery voltage Vbat, the power loss Wloss2 in the time zone of the operation mode S2 is the conduction loss W _1a of the FET _1a and the loss W _d2 due to the body diode _d2. the sum of the _{(Wloss2 = W 1a + W d2} ).

In the operation mode S3, the FET 1d and the body diode d3 are turned on to supply the AC adapter voltage Vadp. Therefore, the power loss Wloss3 in the time zone of the operation mode S3 is the conduction loss W _{1d of the} FET _1d and the loss W due to the body diode d3. the sum of the _{d3 (Wloss3 = W 1d + W} d3).

In the operation mode S4, the FET 1c and the FET 1d are turned on to supply the AC adapter voltage Vadp. Therefore, the loss Wloss4 in the time zone of the operation mode S4 is the sum of the conduction loss W _1c of the FET _1c and the conduction loss W _{1d of the} FET _1d. become _{(Wloss4 = W 1c + W 1d} ).

Here, there are two types of FET power loss: FET conduction loss and body diode loss. The conduction loss Wf of the FET is Wf = I ² × R, where I is the current flowing through the FET and R is the internal resistance of the FET, but the internal resistance R is a very small value (less than about 0.1Ω) Selection), the power when the FET is on is very small. Therefore, the power losses Wloss1 and Wloss4 when supplying power in the steady state of the operation modes S1 and S4 are also small values.

  Further, the power loss Wd due to the body diode is slightly large because Wd = I × Vf and Vf is about 0.5 V, where I is the current flowing through the body diode and Vf is the forward voltage drop. The diode loss is generated only in a short time during the switching operation such as the operation modes S2 and S3, so that the power loss during operation is not greatly affected.

Referring to FIG. 9, the levels of the losses W _1c and W _1d of the FETs _1c and 1d are lower than the losses W _1a and W _{1b of} the FETs 1a and 1b, and the loss of the body diode is smaller than the loss W _{d2 of the} body diode. The level of W _d3 is small.

  Since the battery voltage Vbat is lower than the AC adapter voltage Vadp, assuming that constant power is applied to the load 2, the battery current Ibat that flows to the load 2 when the battery V1 is used is the AC adapter current that flows to the load 2 when the AC adapter V2 is used. The value is larger than Iadp (the current that flows when the voltage is lower is larger).

  Therefore, as can be seen from the above formulas for Wf and Wd, the larger the current, the larger the loss. Therefore, on the battery side and the AC adapter side, even if the same FET conduction loss or body diode loss, A difference will appear in the loss level.

  As described above, in the power supply device 10 of the present invention, when switching from the battery V1 to the AC adapter V2, stable uninterrupted switching can be performed without causing a backflow of current and the like, and during steady operation, Since there is only a small conduction loss of the FET, it is possible to reduce the power loss.

Next, the operation of the FETs 1a to 1d when the power source is switched from the AC adapter V2 to the battery V1 will be described. 10 to 13 are diagrams showing the operations of the FETs 1a to 1d when switching from the AC adapter V2 to the battery V1 is performed. The operation modes S5 to S8 are shown in order in FIGS. In addition, illustration of the voltage detection parts 13-1 and 13-2 and the switching control part 14 is abbreviate | omitted in the figure.
[S5] Power supply from the AC adapter V2 (load voltage V0 = AC adapter voltage Vadp). At this time, the FET switching states are FET1a and 1b are OFF, FET1c and 1d are ON, and the power supply path is AC adapter V2 → FET1d (ON) → FET1c (ON) → load 2.

Since the FET 1b is OFF, the AC adapter current Iadp is in the reverse direction with respect to the body diode d2, and does not flow backward to the battery V1 side. Further, when the FET 1a is turned off, the body diode d1 blocks the output from the battery V1 side.
[S6] When the battery voltage Vbat is detected by the voltage detector 13-1 while the power is being supplied by the AC adapter V2, the switching controller 14 turns on the FET 1a (releases the output cutoff on the battery V1 side), and AC When the adapter V2 is turned off, the battery V1 can be immediately supplied with power. The power supply path is AC adapter V 2 → FET 1 d (ON) → FET 1 c (ON) → load 2. Since Vbat <Vadp, Ibat does not flow.
[S7] When the voltage detection unit 13-2 detects the stop voltage of the AC adapter V2, the switching control unit 14 immediately turns off the FET 1c and FET 1d (prevents backflow from the battery V1 to the AC adapter V2, The output on the AC adapter V2 side is cut off). The power supply path is battery V 1 → FET 1 a (ON) → body diode d 2 → load 2. In this case, the voltage drops by the forward voltage Vf of the body diode d2 of the FET 1b, but no instantaneous interruption occurs.
[S8] The FET 1b is turned ON (preventing the backflow prevention from the AC adapter V2 to the battery V1), Vf by the body diode d2 is removed, and the power supply state from the steady battery V1 is established. The power supply path is battery V 1 → FET 1 a (ON) → FET 1 b (ON) → load 2.

FIG. 14 is a diagram showing a switching sequence from the AC adapter V2 to the battery V1. The switching state of the FET described above with reference to FIGS. 10 to 13 is shown in a time chart.
In the operation mode S5 → S6, when the battery voltage Vbat exceeds the threshold value th1, the FET 1a is immediately turned ON. At this time, the load voltage V0 applied to the load 2 is the AC adapter voltage Vadp.

  In the operation mode S6 → S7, when the AC adapter voltage Vadp falls from the threshold value th2, the FET 1c and FET 1d are immediately turned OFF, and the battery voltage Vbat is applied to the load 2. At this time, the voltage V0 applied to the load 2 drops from the battery voltage Vbat by the forward voltage Vf of the body diode d2.

  However, even if the forward voltage Vf is reduced by about 0.5 V from the battery voltage Vbat, the operation of the load 2 is not hindered, so that no instantaneous interruption occurs in the operation mode S6 → S7. Further, in the operation mode S7 → S8, the FET 1b is turned on, the load voltage V0 becomes the battery voltage Vbat, and the battery V1 is in a steady operation.

FIG. 15 is a diagram showing power loss in each operation mode. In the operation mode S5, the FET 1c and the FET 1d are turned on to supply the AC adapter voltage Vadp. Therefore, the power loss Wloss5 in the time zone of the operation mode S5 is the conduction loss W _1c of the FET _1c and the conduction loss W _{1d of the} FET _1d . the sum _{(Wloss5 = W 1c + W 1d} ).

In the operation mode S6, the AC adapter voltage Vadp is supplied while the FET 1c and the FET 1d remain ON. Therefore, the power loss Wloss6 in the time zone of the operation mode S6 is the conduction loss W _1c of the FET _1c and the conduction loss of the FET 1d as described above. It becomes the sum with W _1d (Wloss6 = W _1c + W _1d ).

In the operation mode S7, the FET 1a and the body diode d2 are turned on to supply the battery voltage Vbat. Therefore, the power loss Wloss7 in the time zone of the operation mode S7 is the conduction loss W _1a of the FET _1a and the loss W _d2 due to the body diode _d2. the sum of the _{(Wloss7 = W 1a + W d2} ). Although diode loss occurs in this time zone, it is limited to only a short time in the middle of switching, so that it does not significantly affect power loss during operation.

In the operation mode S8, the FET 1a and the FET 1b are turned on to supply the battery voltage Vbat. Therefore, the loss Wloss8 in the time zone of the operation mode S8 is the sum of the conduction loss W _1a of the FET _1a and the conduction loss W _{1b of the} FET _1b. consisting of _{(Wloss8 = W 1a + W 1b} ).

  As described above, in the power supply device 10 of the present invention, when switching from the AC adapter V2 to the battery V1, stable uninterruptible switching can be performed without causing a backflow of current, and during steady operation, Since there is only a small conduction loss of the FET, it is possible to reduce the power loss.

  Next, a time constant circuit provided in the output cutoff switch of the FETs 1a and 1d will be described. FIG. 16 shows a time constant circuit. The figure shows the configuration of the peripheral portion where the time constant circuit 15-2 is provided. The time constant circuit 15-2 includes a resistor R2 and a capacitor C2.

  Regarding the connection relationship of the elements around the time constant circuit 15-2, one end of the resistor R2 is connected to the Vd terminal of the switching control unit 14, and the other end of the resistor R2 is connected to the gate of the FET 1d and one end of the capacitor C2. The other end of the capacitor C2 is connected to the source of the FET 1d, the cathode of the body diode d4, and the + side of the AC adapter V2.

  Here, as described above, the load 2 is usually provided with a smoothing capacitor C0. Since the charge is close to 0 in the initial state of the capacitor C0, a large charging current called an inrush current may flow momentarily when the FET 1d is turned on to release the output cutoff from the AC adapter V2. The time constant circuit 15-2 is a circuit for preventing the inrush current from flowing.

  FIG. 17 is a diagram showing the relationship between the gate voltage of the FET 1d and the inrush current. A graph G1 indicates the gate voltage (gate-source voltage) Vgs of the FET 1d, the vertical axis represents the gate voltage Vgs, and the horizontal axis represents time. The graph G2 shows the inrush current flowing into the capacitor C0, the vertical axis is the AC adapter current Iadp, and the horizontal axis is time.

  In the figure, the dotted line display shows the case where the time constant circuit 15-2 is not provided. In this case, since the gate voltage Vgs of the FET 1d is rapidly increased, the FET 1d is rapidly turned on, and the drain current (AC adapter current Iadp) instantaneously takes a large peak value and flows into the load 2 as an inrush current. .

  On the other hand, when there is a time constant circuit 15-2, as indicated by a solid line in the figure, the gate voltage Vgs of the FET 1d starts to rise gently (the current flowing through the time constant circuit 15-2 is caused by the resistor R2). In order to charge the capacitor C2 while being suppressed), as the FET 1d shifts to the ON state, the drain current begins to flow gradually, the peak value of the AC adapter current Iadp is kept low, and the occurrence of an excessive inrush current is suppressed. The

  The gate voltage Vgs is expressed by the following formula (4). In the equation, C is the capacitance of the capacitor C2, and R is the resistance value of the resistor R2.

  From the equation (4), it can be seen that the bias voltage Vd of the FET 1d gradually approaches Vgs over a time constant CR (the larger the value of CR, the more gentle the slope becomes, and the bias voltage Vd becomes Vgs. Will take time to reach). In the above description, the time constant circuit 15-2 provided in the FET 1d on the AC adapter V2 side has been described. However, a similar time constant circuit is provided also in the FET 1a on the battery V1 side (configuration and operation are the same). The explanation is omitted because it is the same).

  Next, a voltage detection unit having a hysteresis comparator will be described. FIG. 18 is a diagram illustrating the configuration of the voltage detection unit. The figure shows the configuration of the periphery of the voltage detector 13-2a provided with a hysteresis comparator. The voltage detector 13-2a includes resistors R5 and R6, a comparator comp2, and a reference voltage source Vr2.

  Regarding the connection relationship of the elements around the voltage detection unit 13-2a, the output terminal of the comparator comp2 is connected to the Vadpon terminal of the switching control unit 14 and one end of the resistor R5. The other end of the resistor R5 is connected to the (+) input terminal of the comparator comp2 and one end of the resistor R6. The other end of the resistor R6 is the source of the FET 1d, the cathode of the body diode d4, and the + side of the AC adapter V2. Connect with. The (−) input terminal of the comparator comp2 is connected to the + side of the reference voltage source Vr2, and the − side of the reference voltage source Vr2 and the − side of the AC adapter V2 are connected to GND (the resistors R5 and R6 and the comparator comp2 are connected to this). A comparator composed of such connections is called a hysteresis comparator).

  The hysteresis comparator detects ripples (pumping) near the detection voltage caused by voltage drop caused by the internal resistance of AC adapter V2, wiring / contact resistance, etc., or false detection due to noise superimposed on the voltage gradient at power-on. It is an element provided to prevent.

  19 and 20 are conceptual diagrams for explaining the operation of the hysteresis comparator. FIG. 19 shows the operation of a normal comparator, and FIG. 20 shows the operation when a hysteresis comparator is used.

  In general, noise is superimposed on the rising slope and falling slope of the power source to cause ripples. For such a voltage waveform, as shown in FIG. 19, when the start / stop voltage of the AC adapter voltage Vadp is recognized with one threshold value TH0, chattering occurs in the detection signal Vadpon of the comparator. This causes a malfunction of FET switching.

  On the other hand, as shown in FIG. 20, the hysteresis comparator has a start voltage threshold value TH1 for the rising slope and a stop voltage threshold value TH2 for the falling slope, and the input voltage (AC adapter voltage Vadp) is When it is lower than the threshold value TH1, the detection signal Vadpon becomes L level, and when the input voltage becomes higher than the threshold value TH1, it becomes H level. Further, when the input voltage becomes lower than the threshold value TH2, the detection signal Vadpon becomes L level. Thus, by using the hysteresis comparator for the voltage detection unit, a relatively stable output can be obtained even if noise is added to the input voltage.

Note that the difference between the thresholds TH1 and TH2 is called a hysteresis voltage, and the larger this is, the stronger the noise. The voltages V _TH1 and V _TH2 and the hysteresis voltage (V _TH1 −V _TH2 ) of the thresholds TH1 and TH2 are calculated by the following equations (5a) to (5c).

  Although the hysteresis comparator of the voltage detection unit 13-2a on the AC adapter voltage V2 side has been described above, a similar hysteresis comparator is provided for the voltage detection unit on the battery V1 side (the configuration and operation are the same). So explanation is omitted).

  Next, the Schottky barrier diode provided in the backflow prevention switch of the FETs 1b and 1c will be described. FIG. 21 is a diagram showing an FET 1c to which a Schottky barrier diode is connected. The Schottky barrier diode sd2 is connected as an external diode in parallel to the body diode d3 of the FET 1c. As for the connection method, the anode of the Schottky barrier diode sd2 is connected to the source of the FET 1c and the anode of the body diode d3, and the cathode of the Schottky barrier diode sd2 is connected to the drain of the FET 1c and the cathode of the body diode d3. .

  The Schottky barrier diode sd2 is a diode whose forward voltage drop is smaller than that of a normal diode. By connecting the Schottky barrier diode sd2 in parallel with the body diode d3 between the drain and source of the FET 1c, it is possible to reduce the decrease in load voltage that is reduced during power supply switching.

FIG. 22 is a diagram showing a forward voltage drop. The vertical axis represents the AC adapter current Iadp, and the horizontal axis represents the forward voltage Vf. Assuming that the forward voltage of the body diode d3 is Vf _d3 and the forward voltage of the Schottky barrier diode sd2 is Vf _sd2 , as can be seen from the figure, Vf _sd2 <Vf _d3 . Therefore, by connecting the Schottky barrier diode in parallel with the body diode, the current flows through the low-voltage Schottky barrier diode side, and it is possible to reduce power loss.

  Next, a communication device to which the power supply device 10 of the present invention is applied will be described. 23 and 24 are diagrams showing the configuration of the communication apparatus. The communication device 100 includes the power supply device 10 of the present invention and reflects each function described above. The communication device 100 can be used in combination with the battery V1 and the AC adapter V2 whose output voltage is higher than that of the battery V1. This is a device that performs information communication by supplying power from the battery V1 or the AC adapter V2.

  The communication device 100 includes FET1a to FET1d, Schottky barrier diodes sd1 and sd2, voltage detection units 13-1a and 13-2a, a switching control unit 14, time constant circuits 15-1 and 15-2, a communication control unit 2a (load 2), a battery V1 and an AC adapter V2.

  Only the peripheral parts of the Schottky barrier diodes sd1 and sd2, the voltage detection unit 13-1a, and the time constant circuit 15-1 will be described with respect to the connection relationship of each element (connection relations of other components have been described). The anode of the Schottky barrier diode sd1 is connected to the drain of the FET 1a, the anode of the body diode d1, the drain of the FET 1b, and the anode of the body diode d2.

  The cathode of the Schottky barrier diode sd1 is the source of the FET 1b, the cathode of the body diode d2, one end of the capacitor C0, the Vin terminal of the communication control unit 2a, the cathode of the Schottky barrier diode sd2, and the source of the FET 1c. Connected to the cathode of the body diode d3.

  The anode of the Schottky barrier diode sd2 is connected to the drain of the FET 1c, the anode of the body diode d3, the drain of the FET 1d, and the anode of the body diode d4.

  For the voltage detector 13-1a, the output terminal of the comparator comp1 is connected to the Vbaton terminal of the switching controller 14 and one end of the resistor R3. The other end of the resistor R3 is connected to the (+) input terminal of the comparator comp1 and one end of the resistor R4. The other end of the resistor R4 is connected to the source of the FET 1a, the cathode of the body diode d1, and the other end of the capacitor C1. Connect to the positive side of the battery V1. The (−) input terminal of the comparator comp1 is connected to the + side of the reference voltage source Vr1, and the − side of the reference voltage source Vr1 is connected to GND.

  For the time constant circuit 15-1, one end of the resistor R1 is connected to the Va terminal of the switching control unit 14, and the other end of the resistor R1 is connected to the gate of the FET 1a and one end of the capacitor C1. The other end of the capacitor C1 is connected to the source of the FET 1a, the cathode of the body diode d1, the other end of the resistor R4, and the + side of the battery V1.

  The operation will be described. Since the detailed operation has been described above, the operation will be briefly described focusing on the operation at the time of switching the power source. In response to switching from the battery V1 to the AC adapter V2, when the AC adapter V2 is activated during operation with the battery V1, the voltage of the AC adapter V2 is detected by the voltage detector 13-2a. When the detection voltage becomes higher than the set voltage (set higher than the starting voltage of the battery V1), the backflow prevention FET 1b on the battery V1 side is turned off to prevent the current from flowing from the AC adapter V2 to the battery V1. .

  Next, the FET 1d is turned on while suppressing the inrush current to the load side capacitor C0 by the time constant circuit 15-2. Here, the load current supplied from the battery V1 side until now switches to the supply from the AC adapter V2.

  However, since the FET 1c is still in the OFF state, the current to the communication control unit 2a is supplied through the Schottky barrier diode sd2 provided between the drain and source of the FET 1c, so that the voltage decreased by Vf of the Schottky barrier diode sd2. Becomes the load voltage of the communication control unit 2a.

  Next, when the FET 1c is turned on, the power supply current does not pass through the Schottky barrier diode sd2 and flows through the FET 1c. Therefore, the voltage Vf rises, and the voltage of the AC adapter V2 is supplied to the load voltage as it is to become a steady state. Thereafter, when the battery voltage is turned off, the FET 1a is turned off (the power supply from the AC adapter V2 is not affected).

  On the other hand, in response to switching from the AC adapter V2 to the battery V1, when the battery V1 is activated during operation with the AC adapter V2, the voltage of the battery V1 is detected by the voltage detector 13-1a including the hysteresis comparator hcomp1. When the detection voltage becomes higher than the set voltage, the output blocking FET 1a on the battery V1 side is turned on to cancel the output blocking. However, since the voltage on the AC adapter V2 side is high, power supply to the communication control unit 2a is still AC. This is done from the adapter V2.

  When the AC adapter V2 stops, the backflow prevention FET 1c and the output cutoff FET 1d on the AC adapter V2 side are immediately turned off to prevent the back flow from the battery V1 to the AC adapter V2 and the output cutoff of the AC adapter V2. I do. At this time, since the FET 1a on the battery V1 side is already ON, power is supplied from the battery V1 to the communication control unit 2a without instantaneous interruption.

  However, since the reverse current prevention FET 1b on the battery V1 side is OFF, the current is supplied through the Schottky barrier diode sd1 provided between the drain and source of the FET 1b. The voltage reduced by Vf becomes the load voltage of the communication control unit 2a.

  Next, when the FET 1b is turned on, the feeding current flows through the FET 1b without passing through the Schottky barrier diode sd1, so that the voltage by Vf rises and the voltage of the battery V1 is supplied to the communication control unit 2a as it is to be in a steady state.

  As described above, during the switching of the power source from the battery V1 to the AC adapter V2 or from the AC adapter V2 to the battery V1, a voltage drop temporarily occurs, but this voltage drop slightly decreases by Vf of the Schottky barrier diode. As a result, there is no hindrance to the operation of the communication control unit 2a, and the power supply is switched without interruption. Further, during steady operation, only the FET conduction loss is achieved, so that power loss can be reduced. Furthermore, since the power supply is switched without using relay switch components, the apparatus can be miniaturized.

FIG. 25 is a diagram showing the operation state of the FET in the steady state of the power supply. The table T1 is a table that summarizes the operation state and power supply source of each FET in the steady state.
[State 1] This is a case where the starting voltages of both the battery V1 and the AC adapter V2 are not detected. In the switching state of the FETs, the FETs 1a to 1d are all OFF, and no power is supplied.
[State 2] This is a case where the starting voltage of the AC adapter V2 is detected. In the switching state of the FET, the FETs 1a and 1b are turned off, the FETs 1c and 1d are turned on, and power is supplied from the AC adapter V2.
[State 3] This is a case where the starting voltage of the battery V1 is detected. In the FET switching state, the FETs 1a and 1b are turned on, the FETs 1c and 1d are turned off, and power is supplied from the battery V1.
[State 4] This is a case where the starting voltages of both the battery V1 and the AC adapter V2 are detected. Since the voltage of the AC adapter V2 is set higher, the FET switching state is that the FETs 1a, 1c, and 1d are turned on, the FET 1b is turned off, and the power supply is supplied from the AC adapter V2 (here The FET 1a is ON, and even when the power supply of the AC adapter V2 is suddenly cut off, power can be immediately supplied to the load 2 through the body diode d2 of the FET 1b).

(Supplementary note 1) In a power supply device that can be used in combination with a first power supply and a second power supply whose output voltage is higher than that of the first power supply.
A first backflow prevention switch installed on the load side of the first power supply line and having a function of preventing a backflow of current from the second power supply to the first power supply; and on the power supply side of the first power supply line And a first output cutoff switch having a function of cutting off the power supply from the first power source when the second power source is used, and the first switch for feeding the first power source to the load And
A second backflow prevention switch installed on the load side of the second power supply line and having a function of preventing a backflow of current from the first power supply to the second power supply; and on the power supply side of the second power supply line And a second output cutoff switch having a function of shutting off the power supply from the second power source when the first power source is used, and a second switch for feeding the second power source to the load And
A first voltage detector for detecting the voltage of the first power supply;
A second voltage detector for detecting the voltage of the second power supply;
A switching control unit for performing ON / OFF switching control of the first switch unit and the second switch unit based on a result of voltage detection;
A power supply device comprising:

  (Supplementary note 2) The first switch unit uses FETs as elements of the first backflow prevention switch and the second output cutoff switch, and in the case of a P-ch MOSFET, each drain is connected. The second switch unit uses a FET as an element of the second backflow prevention switch and the second output cutoff switch, and connects each drain. The power supply apparatus according to appendix 1, wherein the power supply apparatus is configured to be inserted in series on the second power supply line.

  (Supplementary Note 3) When switching from the first power source to the second power source, the switching control unit turns off the first backflow prevention switch when the voltage of the second power source becomes equal to or higher than the starting voltage, After the backflow from the power source to the first power source is prevented, the second output cutoff switch is turned on to release the output cutoff from the second power source, and the second backflow prevention switch is turned on. In the case of switching without interruption and supplying power from the second power source to the load and switching from the second power source to the first power source, when the voltage of the first power source becomes equal to or higher than the starting voltage, the first power source Turn on the output cut-off switch to stand by the power supply from the first power supply, and turn off the second backflow prevention switch and the second output cut-off switch when the voltage of the second power supply falls below the stop voltage. From the first power source to the second power source After the backflow is prevented and the output of the second power supply is shut off, the first backflow prevention switch is turned on to perform a non-instantaneous switching so that power is supplied from the first power supply to the load. The power supply device according to appendix 2.

  (Supplementary note 4) The first output cutoff switch and the second output cutoff switch have a time constant circuit for preventing an inrush current from flowing to a load when the switch is ON. Power supply.

  (Supplementary Note 5) The first voltage detection unit and the second voltage detection unit include a hysteresis comparator for preventing erroneous detection of start / stop voltages of the first power source and the second power source. The power supply device according to appendix 1.

  (Supplementary Note 6) The first backflow prevention switch and the second backflow prevention switch connect a Schottky barrier diode for reducing a decrease in load voltage generated at the time of power supply switching in parallel to the parasitic diode of the FET. The power supply device according to appendix 1, wherein:

(Supplementary note 7) In a communication device that can be used in combination with a battery and an AC adapter having an output voltage higher than that of the battery, and performs information communication by supplying power from the battery or the AC adapter.
A communication control unit which is supplied with power as a load and performs communication control;
Installed on the load side of the battery power line to prevent the back flow of current from the AC adapter to the battery, and installed on the power side of the battery power line when using the AC adapter A battery-side output cut-off switch having a function of shutting off the power supply from the battery, a battery-side switch unit for supplying battery power to the load, and a battery-side switch unit installed on the load side of the AC adapter power line. Installed on the power supply side of the AC adapter power line to prevent the backflow of current from the AC adapter to the AC adapter, and has the function of cutting off the power supply from the AC adapter when using batteries An AC adapter-side output cutoff switch having an AC adapter-side switch section for supplying the AC adapter power to the load, and detecting a battery voltage A battery voltage detection unit, an AC adapter voltage detection unit for detecting an AC adapter voltage, and a switching control for performing ON / OFF switching control of the battery side switch unit and the AC adapter side switch unit based on the result of voltage detection A power supply unit comprising:
A communication apparatus comprising:

  (Supplementary Note 8) The battery side switch unit uses FETs as elements of the battery side backflow prevention switch and the battery side output cutoff switch, and in the case of a P-ch MOSFET, each drain is connected to a battery power line. The AC adapter side switch unit uses FETs as elements of the AC adapter side backflow prevention switch and the AC adapter side output cutoff switch, and connects each drain to connect the AC adapter power supply. The communication apparatus according to appendix 7, wherein the communication apparatus is configured to be inserted in series on a line.

  (Supplementary Note 9) When switching from the battery to the AC adapter, the switching control unit turns off the battery-side backflow prevention switch and prevents backflow from the AC adapter to the battery when the AC adapter voltage exceeds the start-up voltage. , Turn on the AC adapter side output cutoff switch, release the output cutoff from the AC adapter, and turn on the AC adapter side backflow prevention switch to switch the power supply to the load without interruption. When switching from the AC adapter to the battery, when the battery voltage is equal to or higher than the starting voltage, the battery-side output cutoff switch is turned on to standby the power supply from the battery, and when the AC adapter voltage is equal to or lower than the stop voltage, Turn off the AC adapter side backflow prevention switch and the AC adapter side output cut-off switch to remove the AC adapter from the battery. After the AC adapter output is shut off, the battery-side backflow prevention switch is turned on to perform non-instantaneous switching and power is supplied from the battery to the load. 8. The communication device according to 8.

  (Supplementary note 10) The communication according to supplementary note 7, wherein the battery side output cutoff switch and the AC adapter side output cutoff switch have a time constant circuit for preventing an inrush current from flowing to the load when the switch is ON. apparatus.

  (Additional remark 11) The said battery voltage detection part and the said AC adapter voltage detection part have a hysteresis comparator for preventing the misdetection of the starting / stopping voltage of a battery and an AC adapter, The communication apparatus of Additional remark 7 characterized by the above-mentioned .

  (Supplementary Note 12) The battery-side backflow prevention switch and the AC adapter-side backflow prevention switch are configured to connect a Schottky barrier diode in parallel with the parasitic diode of the FET in order to reduce a decrease in the load voltage generated when the power source is switched. The communication device according to appendix 7, characterized by:

It is a principle figure of the power supply device of this invention. It is a figure which shows the structure of a power supply device. It is a figure which shows the relationship between a starting voltage and a power supply voltage. It is a figure which shows operation | movement of FET at the time of switching from a battery to an AC adapter. It is a figure which shows operation | movement of FET at the time of switching from a battery to an AC adapter. It is a figure which shows operation | movement of FET at the time of switching from a battery to an AC adapter. It is a figure which shows operation | movement of FET at the time of switching from a battery to an AC adapter. It is a figure which shows the switching sequence from a battery to an AC adapter. It is a figure which shows the power loss in each operation mode. It is a figure which shows operation | movement of FET at the time of switching from an AC adapter to a battery. It is a figure which shows operation | movement of FET at the time of switching from an AC adapter to a battery. It is a figure which shows operation | movement of FET at the time of switching from an AC adapter to a battery. It is a figure which shows operation | movement of FET at the time of switching from an AC adapter to a battery. It is a figure which shows the switching sequence from an AC adapter to a battery. It is a figure which shows the power loss in each operation mode. It is a figure which shows a time constant circuit. It is a figure which shows the relationship between the gate voltage of FET, and an inrush current. It is a figure which shows the structure of a voltage detection part. It is a conceptual diagram for demonstrating operation | movement of a hysteresis comparator. It is a conceptual diagram for demonstrating operation | movement of a hysteresis comparator. It is a figure which shows FET which connected the Schottky barrier diode. It is a figure which shows a forward voltage drop It is a figure which shows the structure of a communication apparatus. It is a figure which shows the structure of a communication apparatus. It is a figure which shows the operation state of FET in a power supply steady state. It is a figure which shows the structure of the conventional uninterruptible power supply device. It is a figure which shows the structure of the conventional uninterruptible power supply device. It is a figure which shows guard time. It is a figure which shows the drooping voltage which arises during guard time. It is a figure which shows the drooping voltage at the time of providing an inrush current prevention circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Power supply device 11, 12 Switch part 1a, 1d Output cutoff switch 1b, 1c Backflow prevention switch 13-1, 13-2 Voltage detection part 14 Switching control part V1 1st power supply V2 2nd power supply 2 Load

Claims (5)

In a power supply device capable of combined operation of a first power supply and a second power supply having an output voltage higher than that of the first power supply,
A first backflow prevention switch installed on the load side of the first power supply line and having a function of preventing a backflow of current from the second power supply to the first power supply; and on the power supply side of the first power supply line And a first output cutoff switch having a function of cutting off the power supply from the first power source when the second power source is used, and the first switch for feeding the first power source to the load And
A second backflow prevention switch installed on the load side of the second power supply line and having a function of preventing a backflow of current from the first power supply to the second power supply; and on the power supply side of the second power supply line And a second output cutoff switch having a function of shutting off the power supply from the second power source when the first power source is used, and a second switch for feeding the second power source to the load And
A first voltage detector for detecting the voltage of the first power supply;
A second voltage detector for detecting the voltage of the second power supply;
A switching control unit for performing ON / OFF switching control of the first switch unit and the second switch unit based on a result of voltage detection;
A power supply device comprising:   The first switch unit uses FETs as elements of the first backflow prevention switch and the second output cutoff switch. In the case of a P-ch MOSFET, each drain is connected to a first power supply. The second switch section uses FETs as elements of the second backflow prevention switch and the second output cut-off switch, and each drain is connected to the second switch section. The power supply device according to claim 1, wherein the power supply device is configured to be inserted in series on the power supply line.   When switching from the first power supply to the second power supply, the switching control unit turns off the first backflow prevention switch and turns the first power supply from the second power supply to the second power supply when the voltage of the second power supply becomes equal to or higher than the starting voltage. After the backflow to the power source 1 is prevented, the second output cutoff switch is turned on to release the output cutoff from the second power source, and the second backflow prevention switch is turned on to When switching the power supply from the second power source to the load and switching from the second power source to the first power source, when the voltage of the first power source becomes equal to or higher than the starting voltage, the first output cutoff switch is turned on. When the power supply from the first power supply is on standby and the voltage of the second power supply is equal to or lower than the stop voltage, the second backflow prevention switch and the second output cutoff switch are turned off, Prevents backflow from one power supply to a second power supply Then, after the output of the second power supply is cut off, the first backflow prevention switch is turned on to perform a non-instantaneous switching so that power is supplied from the first power supply to the load. Item 3. The power supply device according to Item 2.   2. The power supply apparatus according to claim 1, wherein the first output cutoff switch and the second output cutoff switch have a time constant circuit for preventing an inrush current from flowing to the load when the switch is ON.   The first voltage detection unit and the second voltage detection unit each include a hysteresis comparator for preventing erroneous detection of start / stop voltages of the first power source and the second power source. The power supply device according to 1.

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