JP2008027407A - Dc output power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop a DC output power supply having idling current of zero not by using a transformer and a three-terminal regulator but by using a MOSFET. <P>SOLUTION: A node between C1 and AC of a circuit obtained by serially connecting an AC power supply AC, a diode D, a MOSFET Q and a capacitor C1 is considered as zero point as shown in figure 1. If voltage B is applied between gates of the zero point and the MOSFET Q, voltage of C1 becomes nearly equal to "voltage B minus threshold voltage of Q" and both ends of C1 become the DC output power supply. In the circuit, idling current of exciting current of the transformer and circuit current of the three-terminal regulator becomes nearly zero, current flows in from input if the current flows in a load circuit RL, however, the current from input is zero if the current of the RL is zero. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a DC output power source using a MOSFET or an IGBT.
The embodiments are all N-channel MOSFETs, but P-channel MOSFETs, N-channel IGBTs or P-channel IGBTs can be used with simple circuit changes.
The following confusing terms used in the specification are listed first to make sure.
(1) Input power supply: AC power supply.
(2) Power supply circuit: A power supply circuit that takes the AC power of (1) as an input and outputs the DC of (3). In the circuit of FIG. 1, it is a part of MOSFETQ, capacitor C1, battery B, and resistor R1.
(3) DC output power supply: Both ends of the capacitor C1 used in the power supply circuit of (2) are DC output power supplies.
(4) Output voltage: The voltage of the DC output power source of (3) is the output voltage.
(5) Load circuit current: Current flowing out from the DC output power source of (3) to the load circuit.

In recent large-scale power supply circuits, switching regulator power supply circuits are often used, but a small power supply circuit with a DC of 20V or less and an average current of several tens of mA or less used for a general electronic circuit is a transformer as shown in FIG. In many cases, a voltage obtained by rectifying and smoothing the stepped-down alternating current and controlling the output voltage with a three-terminal regulator or the like is used. In this circuit, an idling current called an exciting current (current that flows in order to generate an output voltage and flows regardless of the presence or absence of the output current) and a three-terminal regulator regardless of the presence or absence of the load circuit current Then, an idling current called a circuit current (also called a bias current) flows to consume power. For example, if the voltage of the DC power supply is 15 V and the circuit current is 10 mA, the power from the circuit current alone is 150 mW. In actual products, there are many products with several watts of standby power due to the exciting current of the transformer and the circuit current of the three-terminal regulator. That is, in the conventional circuit, even if the load circuit current is zero, the power is consumed unless the power is turned off. Further, the transformer is a relatively large and expensive part, and it is desirable that the circuit design can be performed without using the transformer.
Magazine “Transistor Technology” CQ Publishing Co., Ltd., May 2000, P.I. 168-169, FIG. Magazine “Electronic Technology” Nikkan Kogyo Shimbun, April 2001, P.I. 34, FIG.

  In the conventional circuit, as shown in FIG. 4, an AC power supply AC is connected to a transformer TR, a secondary voltage of TR is full-wave rectified by a diode bridge DB, and a voltage controlled by a three-terminal regulator is applied to a load circuit RL. Normally, capacitors C4 and C5 are connected before and after the three-terminal regulator, respectively. In this circuit, as explained in paragraph “0002”, even if the load circuit current is zero, power is generated by the exciting current of the transformer TR and the circuit current of the three-terminal regulator, and the transformer itself is large and expensive. There was a problem of being.

  A diode, a resistor, a MOSFET, and a capacitor are connected in series to the AC power source. The anode of the diode is on the AC power supply side, the drain of the MOSFET is on the resistor side, and the source of the MOSFET is on the capacitor side. In this circuit, if the connection point between the capacitor and the AC power supply is 0, and a DC voltage is applied between the gate of the MOSFET and the 0 point, both terminals of the capacitor become DC output power. Since this power supply has idling current ≈ zero, the input power at idling is on the order of microwatts (μW) due to leakage current.

The proposed power source is suitable for a low-power power source or a power source for an intermittent energization circuit.
In particular, it is an optimal power source for power circuits such as crime prevention / disaster prevention equipment.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

FIG. 1 shows an embodiment according to claim 1 of the present invention, in which an AC power source is half-wave rectified. First, FIG. 1 will be described. Connect the anode of the diode D to the black dot side of the AC power supply AC, connect the resistor R1 to the cathode of D, connect the drain of the MOSFET Q to the other terminal of R1, and connect the black dot side of the capacitor C1 to the source of Q. The non-black dot side of C1 is connected to the non-black dot side of the AC power supply AC, and this connection point is set to zero. In order to smooth the half-wave rectified voltage, a capacitor C2 is connected between the zero point and the cathode of the diode D (the capacitor C2 does not necessarily need to be connected). Further, the battery B is connected between the zero point and the gate of the MOSFET Q with the gate side being positive. The load circuit RL is connected to both ends of the capacitor C1.
Next, FIG. 2 will be described. FIG. 2 shows the relationship between the gate-source voltage Vgs and the drain current Id in the low current portion of the transfer characteristic of the 2SK3109 MOSFET. Assume that the AC power supply AC is a voltage that allows a drain current to flow sufficiently. In the graph of FIG. 2, the gate-source voltage Vgs when the drain current Id = 1 mA is 3.7V. For example, if the voltage of the battery B is 9.5 V and the load circuit current is 1 mA in the power supply circuit that is the dotted line portion of FIG. 1, the voltage of the capacitor C1 = 9.5V-3.7V = 5. It must be 8V (see horizontal axis of drain current = 1 mA in FIG. 2). In summary, if the drain current Id = 0.01 to 0.1 to 10 mA, the gate-source voltage Vgs = 3.4 to 3.5 to 3.7 to 4.0 V, and the capacitor C1 Voltage = 6.1 to 6.0 to 5.8 to 5.5V. The voltage of the capacitor C1 when the drain current Id = 0.01 mA or less is estimated to be 6.1 V from the graph. If this relationship is expressed by a general formula, “C1 voltage≈B voltage−Q threshold voltage” (the threshold voltage is the gate-source voltage when the drain current is 1 mA). Consider this by applying this to the dotted line in FIG. Assume that the voltage of the battery B is 9.5 V and no current flows through the load circuit RL. When this circuit is turned on, the voltage of the capacitor C1 is zero, and the MOSFET Q has a gate-source voltage Vgs≈9.5 V. Therefore, C1 is charged with the drain current Id based on the graph of FIG. Gradually increases (FIG. 2 does not show the graph of the gate-source voltage Vgs = 9.5V portion because the drain current Id is only in the low current portion, but from another source, Id≈15A at Vgs = 9.5V, which is actually a resistance. The current suppressed by the vessel R1 flows). If the voltage of C1 is gradually increased by the charging current to the capacitor C1, the gate-source voltage Vgs of the MOSFET Q is gradually decreased and the drain current Id is also gradually decreased. However, when the voltage of C1 is approximately 6.1 V, C1 is completely charged. Therefore, the drain current Id is zero, the gate-source voltage Vgs is about 3.4 V, and the voltage of the capacitor C1 is about 6.1 V. Next, when the current of ImA stably flows through the load circuit RL, the drain current Id≈1 mA, the gate-source voltage Vgs≈3.7V, and the voltage of the capacitor C1≈5.8V as described above. Similarly, if a current of 0.1 mA stably flows in the load circuit RL, the drain current Id≈0.1 mA, the gate-source voltage Vgs≈3.5V, and the voltage of the capacitor C1≈6.0V.
As described above, the proposed circuit has the following characteristics.
● Circuit with idling current ≈ zero.
● Output voltage ≒ B voltage-Q threshold voltage. The output voltage can be varied by the voltage of B.
● If current flows through the load path RL, current flows from the input power source to RL.
● The voltage fluctuation of the capacitor C1 due to the fluctuation of the load circuit current is slight.
● Since battery B has zero current, it has the same life as natural consumption. Instead of the battery B, a “zener diode + resistor” may be used. The resistor at that time operates with a high resistance of several hundred MΩ.
Magazine "Electronic Technology" Nikkan Kogyo Shimbun, October 2003, P.I. 82, FIG.

  Next, the operation of FIG. 1 will be described. If the black dot side of the AC power supply AC is positive in a stable operation state, the current flows through the AC power supply AC-diode D) -resistor R1-MOSFET Q-capacitor C1-AC power supply AC, and as described in "0007", "C1 The voltage of C1 is applied to the load circuit RL as a DC output power source. At this time, if the load circuit current is zero, the input current ≈ zero, so the input power ≈ zero. When the black dot side of the AC power source AC is positive and the load circuit current flows, the AC power source AC-diode D-resistor R1-MOSFET Q-load circuit RL-AC power source AC flows. When the non-black dot side of the AC power supply AC is positive, there is a diode D, so that no current flows from the AC power supply AC to the load circuit RL, but current flows through the capacitor C1-load circuit RL-capacitor C1. That is, this circuit is a simple circuit without using a transformer, and becomes a DC output power source that is small, light, inexpensive, and has low loss.

FIG. 3 shows an embodiment according to claim 1 of the present invention, in which an AC power source is full-wave rectified. This circuit connects the AC power supply AC to the AC terminal of the diode bridge DB. The resistor R1 is connected to the output positive terminal of the diode bridge DB, the other terminal of R1 is connected to the drain of the MOSFET Q, the capacitor C1 is connected to the source of Q, and the other terminal of C1 is the zero point of DB. Connect to the negative output terminal. The capacitor C3 and the anode of the Zener diode ZD are separately connected to the zero point, another terminal of C3, the cathode of ZD, the gate of the MOSFET Q, and the resistor R2 are connected, and the other terminal of R2 is the output positive of the diode bridge DB. Connect to the terminal. The load circuit RL is connected to both terminals of the capacitor C1.
The operation of this circuit will be described. The voltage generated in the series circuit of the resistor R2 and the Zener diode ZD becomes a DC voltage by the capacitor C3, and a DC voltage is applied between the zero point and the gate of the MOSFET Q as in the circuit of FIG. The other operation is only a difference in which the half-wave rectifier circuit of the first embodiment is changed to a full-wave rectifier circuit, and thus detailed description of the operation is omitted. That is, this circuit is also a simple circuit without using a transformer, and becomes a DC output power source that is small, lightweight, inexpensive, and has low loss.

  It is an example of the circuit which carried out the half wave rectification of AC power supply in 1st Example of this invention.   It is a graph of the transfer characteristic of the low current part of MOSFET.   It is an example of the circuit which carried out the full wave rectification of AC power supply in 2nd Example of this invention.   This is an example in which a transformer and a three-terminal regulator are used in a conventional circuit.

Explanation of symbols

AC AC power supply RL Load circuit Q MOSFET
D Diode DB Diode Bridge ZD Zener Diode R1-R2 Resistor C1-C5 Capacitor TR Transformer

Claims (1)

The power supply which makes the both ends of the capacitor | condenser of one power supply circuit selected from the following A group make a DC output power supply terminal.
Group A a. Connect the rectifier circuit to the AC power source, connect the output positive terminal of the rectifier circuit to the drain of the N-channel MOSFET, connect the source of the MOSFET and the capacitor, connect the other terminal of the capacitor and the output negative terminal of the rectifier circuit The power supply circuit which applied the voltage which made the gate side positive between the connection point of the connected circuit, and the gate of said MOSFET.
b. Connect the rectifier circuit to the AC power supply, connect the output negative terminal of the rectifier circuit to the drain of the P-channel MOSFET, connect the source of the MOSFET and the capacitor, connect the other terminal of the capacitor and the output positive terminal of the rectifier circuit A power supply circuit in which a negative voltage is applied between a connection point of a connected circuit and the gate of the MOSFET.
c. Connect the rectifier circuit to the AC power supply, connect the output positive terminal of the rectifier circuit to the collector of the N-channel IGBT, connect the emitter and capacitor of the IGBT, and connect the other terminal of the capacitor and the output negative terminal of the rectifier circuit. The power supply circuit which applied the voltage which made the gate side positive between the connection point of the connected circuit, and the gate of said IGBT.
d. Connect the rectifier circuit to the AC power supply, connect the negative output terminal of the rectifier circuit to the collector of the P-channel IGBT, connect the emitter and capacitor of the IGBT, connect the other terminal of the capacitor and the output positive terminal of the rectifier circuit. The power supply circuit which applied the voltage which made the gate side negative between the connection point of the connected circuit, and the gate of said IGBT.

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