JP2986978B2 - Multi-output type switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a power supply for a television receiver, a power supply for a video tape recorder, and the like, and more particularly, to a power supply for use in an electronic apparatus which uses a plurality of power supplies having different power supply voltages. The present invention relates to a multi-output type switching power supply device.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a conventional example of a ringing choke converter type multiple output type (two output type) switching power supply.

The power supply terminal 1 to which the DC voltage Ein is supplied is
The primary winding 2P of the converter transformer 2 and the collector of the NPN transistor 3 forming a switching element.
Grounded via a series circuit of emitters. Further, a series circuit of a capacitor 4 and a resistor 5 constituting a snubber circuit for absorbing surge is connected in parallel with the collector and the emitter of the transistor 3.

The power supply terminal 1 is connected to the base of the transistor 3 via a starting resistor 6 and a series circuit of a parallel circuit 10. The parallel circuit 10 includes a diode 7,
A capacitor 9 is connected in parallel to a series circuit of a resistor 8.

[0005] One end of the base winding 2B of the transformer 2 is grounded, and the other end is connected to a connection point of the resistor 6 and the parallel circuit 10.

The parallel circuit 10 and the transistor 3
The base connection point is grounded via the collector / emitter of an NPN transistor 11 for base current control.

[0007] One end of the secondary winding 2S of the transformer 2 is grounded, and the other end of the secondary winding 2S is an anode of a rectifying diode 12.
It is grounded through a series circuit of a cathode and a capacitor 13 for smoothing. Then, a DC voltage (first output voltage) E1 obtained at a connection point between the diode 12 and the capacitor 13 is led out to the output terminal 14 via the switch S1.

The output terminal 14 is grounded via a series circuit including a switch S1, a resistor 15, a variable resistor 16 and a resistor 17. The voltage obtained at the mover of the variable resistor 16 is supplied to a comparator 18 and compared with a reference voltage Vref output from a reference power supply 18a. From the comparator 18, a signal which becomes higher as the voltage obtained at the movable element of the variable resistor 16 becomes higher is output. The output signal of the comparator 18 is supplied to the base of the transistor 11 via the resistor 19. Note that the transistor 11
, The comparator 18 and the resistor 19 constitute a base current control circuit A.

One end of the tertiary winding 2T of the transformer 2 is grounded, and the other end of the tertiary winding 2T is an anode of a rectifying diode 20.
It is grounded via a series circuit of a cathode and a capacitor 21 for smoothing. The connection point between the diode 20 and the capacitor 21 is connected to the input side of the control circuit 22, the output side of the control circuit 22 is grounded via the capacitor 23, and the output voltage of the control circuit 22 (second output voltage) E
2 is output to the output terminal 24 via the switch S2.

In the circuit shown in FIG. 3, a power supply circuit for outputting a DC voltage E1 (hereinafter referred to as an E1 power supply circuit) is a power supply circuit for a large load, for example, for a television receiver. 140V, about 80W
It is. A power supply circuit that outputs the DC voltage E2 (hereinafter, referred to as an E2 power supply circuit) is a power supply circuit for a light load, for example, a video tape recorder, and has an output voltage and output power of about 18 V and about 20 W, for example. The switches S1 and S2 in FIG. 3 may be manually operated or controlled by a microcomputer.

Next, using the signal waveform diagram of FIG.
The operation of the circuit of FIG.

When the DC voltage Ein is supplied to the power supply terminal 1, a starting current is supplied to the base of the transistor 3 via the resistor 6 and the parallel circuit 10. The primary winding 2P and the base winding 2B of the transformer 2 are connected so as to provide a positive feedback, immediately start oscillating, and the amplitude of the voltage VB induced in the base winding 2B increases ( 4H), the transistor 3 is immediately turned on.

When the transistor 3 is turned on, a reverse voltage is applied to the diode 12 connected to the secondary winding 2S of the transformer 2 and the diode 20 connected to the tertiary winding 2T (see FIG. 3 illustrates a voltage Vs induced in the secondary winding 2S, and a voltage Vt induced in the tertiary winding 2T.
Is different from the voltage Vs, but has a pulse waveform similar to that of the voltage Vs).
No current flows through. Therefore, the load on the transistor 3 is only the inductance of the transformer 2 and the collector current IC increases linearly (shown in FIG. 1A).

FIG. 4B shows the voltage VCE between the collector and the emitter of the transistor 3, and FIG. 4C shows the base current IB of the transistor 3. The base current IB is a composite of the current ID1 flowing through the series circuit of the diode 7 and the resistor 8 and the current IC1 flowing through the capacitor 9. That is, when the transistor 3 is turned on, the forward voltage VB induced in the base winding 2B of the transformer 2
As a result, an attenuation current IC1 flows through the capacitor 9 with a time constant determined by the capacitance of the capacitor 9, the resistance of the base winding 2B, and the like (shown in FIG. 4D). The capacitor 9
When the voltage between both ends reaches the forward drop voltage of the diode 7, the current ID1 is supplied to the series circuit of the diode 7 and the resistor 8.
Flows (illustrated in FIG. E).

As described above, the collector current IC that linearly increases remains unchanged even after increasing to hFE times the base current IB.
It continues to increase during the storage time tstg of the transistor 3 (shown in FIG. 4A). When the storage time tstg elapses, the current sharply decreases, and at the same time, a reverse voltage VB is generated in the base winding 2B (shown in FIG. 7H), and the base current IB of the transistor 3 becomes a reverse bias current (see FIG. As shown in FIG. C), the transistor 3 is turned off.

Here, the maximum value ICP of the collector current IC will be described.

That is, the collector current IC is given by: IC = I
Due to the relationship of B · hFE, the base current IB increases linearly at the same time as the base current IB increases. The maximum value ICP of the collector current IC is as follows.

ICP = IBP · hFE + tstg · Ein / LP (1) In this equation, IBP is the maximum value of the base current IB of the transistor 3, and LP is the inductance of the primary winding 2P of the transformer 2. .

Next, when the transistor 3 is turned off, the energy accumulated in the core of the transformer 2 during the on-period of the transistor 3 is released with a negative change rate of the magnetic flux. Generates a voltage with the “•” mark side being negative.

At this time, a current IL that linearly decreases starts flowing through the primary winding 2P of the transformer 2 as shown in FIG. 4F. Similarly, a current ID2 that decreases linearly starts flowing in the diode 12 connected to the secondary winding 2S, as shown in FIG. The same current ID3 starts flowing through the diode 20 connected to the tertiary winding 2T, though the level is different from ID2.

In such a state, the release of the energy stored in the core of the transformer 2 is completed, and the currents IL and I
When D2 and ID3 become 0, there is no change in the magnetic flux in the transformer 2, and a voltage in the opposite direction is generated in each winding of the transformer 2. Therefore, the base winding 2B of the transformer 2
Is also a forward voltage, and a base current flows in a direction to turn on the transistor 3. As a result, the transistor 3 is turned on, and the same operation as described above is repeated.

By such a repetitive operation, a rectangular wave voltage VS as shown in FIG. 4I is obtained in the secondary winding 2S of the transformer 2, which is rectified and smoothed, and the DC voltage E1 is output to the output terminal 14. can get. Also, a voltage Vt having the same waveform as that of FIG. 4I is obtained in the tertiary winding 2T, which is rectified and smoothed and controlled to obtain a DC voltage E2.

Next, the case where the DC voltage E1 fluctuates will be described.

When the DC voltage E1 increases, the variable resistor 1
The voltage obtained at the mover 6 increases, and the level of the output signal of the comparator 18 increases. Therefore, transistor 1
One base current increases, and at the same time its collector current increases. Thereby, the base current IB of the transistor 3
Is reduced, and the maximum value ICP of the collector current IC is also reduced from the relationship of the above equation (1), so that the ON period of the transistor 3 is shortened (shown in FIG. 4J).

As described above, when the ON period of the transistor 3 is shortened, the amplitude of the rectangular wave voltage VS obtained in the secondary winding 2S of the transformer 2 in the positive direction decreases (shown in FIG. K). Therefore, the DC voltage E obtained at the output terminal 14
1 is controlled in a lowering direction.

Conversely, when the DC voltage E1 decreases, the control is performed in the opposite manner as described above, and the DC voltage E1
Is controlled to increase.

From such an operation, the DC voltage E1 obtained at the output terminal 14 is stabilized. By changing the position of the mover of the variable resistor 16, the DC voltage E1
Can be changed.

When the DC voltage E1 fluctuates, the transistor 3
Of the AC current induced in the converter transformer 2 due to the variation of the base current IB, the AC voltage (pulsed voltage) Vt generated in the tertiary winding 2T also changes. Controlled by the control circuit 22,
The control circuit 22 outputs a DC voltage E2 having a constant voltage value.

As described above, the conventional multi-output type switching power supply shown in FIG. 3 obtains two kinds of stable DC power supplies.

[0030]

As described above, for the base current and the ON period of the transistor 3, the output voltage value of the DC power supply having a large capacity or the output voltage value (E1 in FIG. 3) having a strict voltage specification is detected. Was controlled. For this reason, the value of the output voltage Vt of the tertiary winding 2T of the transformer 2 differs depending on whether power is supplied to the load connected to the output terminal 14. When power is supplied to the load connected to the output terminal 14 (when the switch S1 is on), the base current IB of the transistor 3 is controlled to increase, and as a result, the primary winding of the transformer 2 2P
And the AC voltage value induced in the secondary winding 2S increases, and the value of the voltage E1 is kept constant. At this time, although the value of the AC voltage Vt induced in the tertiary winding 2T also increases, the control circuit 22 controls the output voltage E2 to be constant.

Conversely, when power is not supplied to the load connected to the output terminal 14 (when the switch S1 is off), the tertiary winding is reversed in contrast to the case where power is supplied. Although the value of the AC voltage Vt induced by 2T becomes small, the value of the output voltage E2 is kept constant by the control circuit 22.

As described above, the control circuit 22 controls the tertiary winding 2
In order to keep the value of the voltage E2 constant in response to the change in the voltage Vt induced by T, heat is internally generated due to power loss. Therefore, a heat sink for heat dissipation is required,
The required space increases. In addition, since heat dissipation causes heat rise in the peripheral portion, the peripheral portion must also be designed in consideration of the heat rise, and the setting cost increases.

The present invention has been made in view of such circumstances, and has as its object to stabilize a plurality of types of DC output voltages so that no power loss occurs and therefore heat dissipation is prevented. An object of the present invention is to provide a multi-output type switching power supply device which does not cause any problem.

[0034]

In order to solve the above-mentioned problems, according to the present invention, a DC power supply is connected to a series circuit of a switching element composed of a primary winding of a converter transformer and a transistor, and a DC power supply is connected to the converter. A multi-output switching power supply in which a rectifying and smoothing circuit for obtaining first and second output voltages is connected to the secondary winding and the tertiary winding, a first detection unit having a first selection transistor; And second detection means having a second selection transistor, wherein the first detection means comprises:
When the first output voltage is supplied to the load, the first selection transistor is turned on to operate, generating a detection voltage value corresponding to the first output voltage value, and Operates when the second output transistor is turned on when the first output voltage is not supplied to the load, and generates a detection voltage value corresponding to the second output voltage value. It is something to do.

[0035]

In the multi-output switching power supply according to the present invention, as shown in FIG. 1, when the first output voltage E1 is supplied to the load, the first output voltage E1 is controlled and the first output voltage E1 is controlled. When the voltage E1 is not supplied to the load, the second output voltage E2 is to be controlled. First
When the output voltage E1 is supplied to the load, the first
When the selection transistor 28 is turned on, the first
Operates, and supplies a detected voltage value corresponding to the first output voltage E1 to the base current control circuit A. As a result, the first output voltage value E1 is controlled to a predetermined value. Further, when the first output voltage E1 is not supplied to the load, the second selection transistor 32 is turned on, the second detection means 36 operates, and the second output voltage E1 is turned off.
2 is supplied to the base current control circuit A. Thereby, the value of the second output voltage E2 is controlled to a predetermined value. Thus, the first or second output voltage E1
Alternatively, the first or second selection transistor 28 or 32 for controlling the value of E2 performs an on / off operation, and almost no power loss occurs, so that no measures for heat dissipation are required.

[0036]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention. 3, the same or corresponding parts as those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the embodiment shown in FIG. 1, a resistor 25, a variable resistor 26, a first selecting transistor 28 and a resistor 29 are connected in series, and these constitute a first detecting means 30. . This first detecting means 30 detects the voltage E
3 is a circuit for keeping the value of 1 constant.
5 and 17 and the variable resistor 16, and a connection point between the transistor 28 and the resistor 29 is connected to the plus terminal of the comparator 18. The resistor 27 is a bias resistor for the transistor 28. Also, the second selection transistor 32, the resistor 33 and the variable resistor 34
Are connected in series, and these are connected to the second detecting means 36.
Is configured. The resistors 31 and 35 are transistors 3
2 for the base bias. This second detecting means 36
Is a circuit for keeping the value of the voltage E2 constant similarly to the control circuit 22 in FIG.

In the above configuration, the switches S1, S2
The operation when both are on will be described. Power supply terminal 1
Is supplied to the base of the transistor 3 via the resistor 6, oscillation is started, and the AC voltage (pulse) is applied to the secondary winding 2S and the tertiary winding 2T of the transformer 2. State voltages) Vs and Vt are induced. As a result, the DC voltage E1,
E2 occurs. In FIG. 1, the voltage value is E1> E.
There is a relationship of 2.

At this time, since the switch S1 is on, the voltage E1 is applied to both the base of the NPN transistor 28 and the base of the PNP transistor 32, and the transistor 28 is turned on and the transistor 32 is turned off.

Therefore, a voltage e1 obtained by dividing the DC voltage E1 is applied to the positive terminal of the comparator 18, and the value of the voltage e1 and the value of the reference voltage Vref are compared by the comparator 18, and the difference ( A voltage proportional to (e1-Vref) (hereinafter, referred to as a proportional voltage) is output from the comparator 18. The collector current of the transistor 11 is controlled by the proportional voltage, and as a result, the base current IB is controlled.

In this way, the value of the voltage E1 is kept constant. When the switch S1 is on, the E1 power supply circuit is in the load state, and the voltage induced in the tertiary winding 2T is in a higher voltage state than in the no-load state. In this state, when the switch S2 is turned on, the value of the voltage E2 becomes a predetermined value.
The turn ratio between the primary winding 2P and the tertiary winding 2T is set.

The value of the voltage e1 is such that the resistance values of the resistors 25 and 29 are R1 and R2, and the resistance value of the variable resistor 26 is V
Assuming that R1 is R1 and the ON resistance value of the transistor 28 is r1, e1 = E1 · R2 / (R1 + R2 + VR1 + r) (2) As can be seen from equation (2), the value of e1, ie, E
Since the value of 1 changes according to the resistance value VR1 of the variable resistor 26, the resistance value VR1 is adjusted to set the value of E1 to a predetermined value.

Next, the operation when the switch S1 is turned off will be described. Since switch S1 is off, N
Zero voltage is applied to the base of the PN transistor 28 and the base of the PNP transistor 32, and the transistor 28 is turned off and the transistor 32 is turned on.

Therefore, the divided voltage e2 of the DC voltage E2
Is applied to the plus terminal of the comparator 18, and the voltage E2 is controlled to be constant, as in the case of the voltage E1 control. Assuming that the ON resistance value of the transistor 32 is r2, the value of the resistor 33 is R3, and the value of the variable resistor 34 is VR2, the value of the voltage e2 is e2 = E2 / R2 / (r2 + R3 + VR2 + R2) (3) Become.

As can be seen from equation (3), the value of e2, that is, the value of E2 changes according to the resistance value VR2.
The value of E2 is adjusted to a predetermined value by adjusting the value of E2. In addition,
The setting is performed while the switch S2 is turned on (load state).

As described above, in the circuit of FIG. 1, the output DC voltage to be controlled differs depending on whether the switch S1 is on or off, and the voltage E1 is on when the switch S1 is on.
Is a control target, and the value of the voltage E2 is a predetermined value determined by the number of turns of the tertiary winding 2T. When the switch S1 is off, the voltage E1 does not need to be controlled, and only the voltage E2 is controlled.

In the above embodiment, the selection transistors 28 and 32 perform only ON and OFF operations, and the active region is not specified. As a result, the selection transistor 28,
32 has almost no power loss (collector loss). Further, by setting the input impedance of the comparator 18 to a high impedance, the power loss in the resistors and the variable resistors constituting the detecting means 30 and 36 can be reduced. As described above, since the power loss can be made much smaller than that of the conventional circuit shown in FIG. 3, it is not necessary to consider the influence of heat dissipation due to the power loss, and therefore, a heat sink is not required. Therefore, this circuit is more advantageous in terms of space and design cost than the conventional circuit.

FIG. 2 is a circuit diagram showing another embodiment of the present invention, in which the primary side and the secondary side of the transformer 2 are completely electrically separated by a photocoupler. If the value of the detection voltage e1 or e2 generated in the resistor 29 in accordance with the presence or absence of the supply of the first output voltage E1 to the load is higher than the value of the reference voltage Vref of the reference power supply 18, the transistor 3
7 is turned on, a current flows through the diode 38a of the photocoupler 38 due to the voltage E2, and the diode 38a emits light. The phototransistor 38b of the photocoupler 38 receives the output light of the diode 38a, and a collector current flows in accordance with the amount of received light, that is, the amount of light emitted by the diode 38a. As a result, the base current IB is controlled.

In the above embodiment, the case where the present invention is applied to the switching power supply device of the ringing choke converter system has been described. However, the present invention is not limited to this, and the present invention is not limited thereto.
The present invention can be applied to a forward system, a flyback system, and the like, and achieves the same effect.

[0050]

As described above, according to the present invention,
Since the first or second output voltage can be controlled without causing power loss in the first or second selection transistor, there is no need for a space for a heat dissipation plate for heat dissipation based on the power loss. In addition, there is no need for a design measure against heat dissipation, and the design cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional multi-output type switching power supply device.

FIG. 4 is a waveform diagram showing signal waveforms in the multi-output switching power supply device.

[Explanation of symbols]

 2 Converter Transformer 3 Transistor 2P Primary Winding 2S Secondary Winding 2T Tertiary Winding 2B Base Winding 6 Starting Resistor 29 First Selection Transistor 32 Second Selection Transistor

Claims (1)

(57) [Claims] 1. A DC power supply is connected to a series circuit of a switching element including a primary winding of a converter transformer and a transistor, and a secondary winding and a tertiary winding of the converter transformer have first and second outputs. A multi-output switching power supply to which a rectifying / smoothing circuit for obtaining a voltage is connected, a first detection unit having a first selection transistor,
Second detection means having a second selection transistor, wherein the first detection means turns on the first selection transistor when the first output voltage is supplied to a load. And generates a detection voltage value corresponding to the first output voltage value. The second detection means performs the second selection when the first output voltage is not supplied to a load. A multi-output switching power supply device that operates by turning on a transistor for use and generates a detection voltage value corresponding to the second output voltage value.