JPH0595675A - Multiple output type switching power supply equipment - Google Patents

Abstract

PURPOSE:To eliminate heat dissipation and avoid power loss in stabilizing a plurality of DC output voltages. CONSTITUTION:The first detected voltage e1 corresponding to the first output voltage E1 is compared to the first reference voltage v1 as an output voltage from the second comparison means 32 by the first comparison means 28, the second reference voltage Vref is compared to the second detection voltage e2 corresponding to the second output voltage E2 by the second comparison means 32, and the first reference voltage v2 is output from the comparison means 32. The level of induced AC voltage of a converter transformer 2 is controlled by the output voltage from the first comparison means 28, and the first or second output voltage E1 or E2 is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for use in electronic equipment by using a plurality of types of power sources, especially two types of power sources having different power source voltages, such as a power source for a television receiver and a power source for a video tape recorder. The present invention relates to a multi-output type switching power supply device.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional example of a ringing choke converter type multi-output type (two-output type) switching power supply device.

The power supply terminal 1 to which the DC voltage Ein is supplied is
The collector of the NPN transistor 3 which forms the primary winding 2P of the converter transformer 2 and the switching element
It is grounded through the series circuit of the emitter. In addition, a series circuit of a capacitor 4 and a resistor 5 forming a snubber circuit for absorbing surge is connected in parallel with the collector / emitter of the transistor 3.

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

Further, one end of the base winding 2B of the transformer 2 is grounded, and the other end is connected to the connection point of the resistor 6 and the parallel circuit 10.

In addition, the parallel circuit 10 and the transistor 3
The connection point of the bases is grounded via the collector / emitter of the NPN transistor 11 for controlling the base current.

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

The output terminal 14 is grounded via a series circuit of 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 the comparator 18 and compared with the reference voltage Vref output from the reference power supply 18a. The comparator 18 outputs a signal that becomes higher level as the voltage obtained at the mover of the variable resistor 16 becomes higher. 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 form a base current control circuit A.

Further, one end of the tertiary winding 2T of the transformer 2 is grounded and the other end thereof is an anode of the rectifying diode 20.
It is grounded through a series circuit of a cathode and a smoothing capacitor 21. 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 led to the output terminal 24 via the switch S2.

In the circuit of FIG. 4, a power supply circuit for outputting a DC voltage E1 (hereinafter referred to as E1 power supply circuit) is a power supply circuit for heavy loads, for example, for a television receiver, and the output voltage and output power are, for example, 115V to 140V, about 80W
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 the output voltage and the output power are, for example, about 18V and about 20W. The switches S1 and S2 in FIG. 4 may be manually operated or controlled by a microcomputer.

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

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 be a positive feedback, and immediately start oscillating, and the amplitude of the voltage VB induced in the base winding 2B becomes large ( As shown in FIG. 5H), the transistor 3 is turned on immediately.

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. The voltage Vs induced in the secondary winding 2S is shown in the figure: The voltage Vt induced in the tertiary winding 2T.
Also, although the level is different from the voltage Vs, it has a waveform similar to Vs), but no current flows through the diode 12 and the diode 20. Therefore, the load of the transistor 3 is only the inductance of the transformer 2, and the collector current IC increases linearly (shown in FIG. A).

FIG. 5B shows the collector-emitter voltage VCE of the transistor 3, and FIG. 5C shows the base current IB of the transistor 3. The base current IB is a combination 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 and the resistance of the base winding 2B (shown in FIG. 5D). Also, the capacitor 9
When the voltage across the diode reaches the forward voltage drop of the diode 7, a current ID1 is applied to the series circuit of the diode 7 and the resistor 8.
Flows (illustrated in FIG. 8E).

As described above, the collector current IC which increases linearly increases, 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 A of the same figure). When the accumulation time tstg has elapsed, the current sharply decreases, and at the same time, a reverse voltage VB is generated in the base winding 2B (shown in FIG. 6H), and the base current IB of the transistor 3 becomes a reverse bias current (same as the reverse bias current). (Illustrated 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 IC = I
Due to the relationship of B · hFE, the base current IB increases linearly at the same time. The maximum value ICP of this collector current IC is as follows.

ICP = IBP · hFE + tstg · Ein / LP (1) In this formula, 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 discharged because the rate of change of the magnetic flux becomes negative, so that the energy is accumulated in each winding of the transformer 2. Generates a voltage with the "." Mark side being negative.

At this time, a current IL that linearly decreases starts to flow in the primary winding 2P of the transformer 2 as shown in FIG. 5F. Similarly, in the diode 12 connected to the secondary winding 2S, a current ID2 that linearly decreases as shown in FIG. Further, a similar current ID3 flows through the diode 20 connected to the tertiary winding 2T, though the level is different from that of ID2.

In this 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
The voltage VB induced in the transistor also becomes 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.

As a result of such repetitive operation, a rectangular wave voltage VS as shown in FIG. 5I is obtained at the secondary winding 2S of the transformer 2, which is rectified and smoothed and a DC voltage E1 is output to the output terminal 14. can get. Further, a voltage having a waveform similar to that of FIG. 5I is obtained also 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 of No. 6 becomes high, and the level of the output signal of the comparator 18 becomes high. Therefore, transistor 1
The base current of 1 increases, and at the same time, its collector current also increases. As a result, the base current IB of the transistor 3
Decreases, the maximum value ICP of the collector current IC also decreases from the relationship of the above equation (1), and the ON period of the transistor 3 eventually becomes shorter (shown in FIG. 5J).

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 is reduced (shown in K in the same figure). Therefore, the DC voltage E obtained at the output terminal 14
1 is controlled so as to decrease.

On the contrary, when the DC voltage E1 becomes low, the DC voltage E1 obtained at the output terminal 14 is controlled contrary to the above.
Is controlled to increase.

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

As the DC voltage E1 changes, the transistor 3
Change in the base current IB changes the value of the AC voltage induced in the converter transformer 2 and thus the AC voltage Vt generated in the tertiary winding 2T. This change is controlled by the control circuit 22. Then, the DC voltage E2 having a constant voltage value is output from the control circuit 22.

Thus, the conventional multi-output type switching power supply device shown in FIG. 4 obtains two types of stabilized DC power supplies.

[0030]

As described above, the base current and the ON period of the transistor 3 are detected by detecting the output voltage value of the DC power source having a large capacity or the output voltage value having a strict voltage specification (E1 in FIG. 4). Was controlled. Therefore, the value of the output voltage Vt of the tertiary winding 2T of the transformer 2 is
It depends on whether or not power is supplied to the load connected to the output terminal 14. When power is being 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 is increased. The AC voltage value induced in 2P and the secondary winding 2S increases, and the value of the voltage E1 is kept constant. At this time, the value of the AC voltage Vt induced in the tertiary winding 2T also increases, but the control circuit 22 controls the output voltage E2 to be constant.

On the contrary, when power is not being supplied to the load connected to the output terminal 14 (when the switch S1 is off), contrary to the case where the power is being supplied, the tertiary winding Although the value of the AC voltage Vt induced in 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 includes the tertiary winding 2
Since the value of the voltage E2 is kept constant corresponding to the change of the voltage Vt induced in T, power loss is generated inside, and thus heat is generated. Therefore, a heat dissipation plate for dissipating heat is required, and the required space increases. Further, since heat dissipation causes heat increase in the peripheral portion, the peripheral portion also has to be designed in consideration of the heat increase, which increases the design cost.

The present invention has been made in consideration of the above circumstances, and an object thereof is to prevent power loss from occurring when the output voltage of a light load power supply circuit is stabilized.
Therefore, it is to obtain a multi-output type switching power supply device which does not generate heat dissipation.

[0034]

In order to solve the above-mentioned problems, in 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 In a multi-output type switching power supply device in which a rectifying / smoothing circuit for obtaining first and second output voltages is connected to the secondary winding and the tertiary winding, a first detection voltage corresponding to the first output voltage and a first detection voltage A first comparison means for comparing with a first reference voltage; and a second comparison means for comparing a second detection voltage corresponding to the second output voltage with a second reference voltage, The first reference voltage is the output voltage of the second comparing means, and the level of the AC voltage induced in the converter transformer is controlled by the output voltage of the first comparing means. A.

[0035]

In the multi-output switching power supply device according to the present invention, as shown in FIG. 1, by rectifying and smoothing the induced AC voltages Vs and Vt, the first output voltage E1 and the second output voltage E2 are It occurs on the cathode side of the diode 12 and the cathode side of the diode 20.

The first output voltage E1 is applied to the resistors 25 and 27.
The voltage is divided by the variable resistor 26, and the first detection voltage e1 is generated at the positive terminal of the first comparison means 28. Further, the second output voltage E2 is divided by the resistors 29 and 31 and the variable resistor 30 to generate the second detection voltage e2 at the negative terminal of the second comparing means 32.

The comparing means 32 compares the detected voltage e2 with the second reference voltage Vref and outputs the first reference voltage v2. The comparison means 28 compares the first detection voltage e1 with the second reference voltage v2 and outputs the voltage v1, and controls the base current of the transistor 3 via the transistor 11.
The on / off time ratio of the pulse voltage induced in the transformer 2 is controlled to control the levels of the first and second output voltages.

In this way, the first and second output voltages are controlled to predetermined values. Note that turning on and off the switches S1 and S2 does not affect the circuit operation of FIG.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, the same or corresponding parts as those in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, the resistor 25 and the variable resistor 2
6 and the resistor 27 are connected in series between the cathode of the diode 12 and the ground, one end of the resistor 27 being the first
Is connected to the positive terminal of a comparator 28 as a comparison means of the above, and the other end is grounded. A first detection voltage e1 is generated at the connection point between the resistor 27 and the positive terminal of the comparator stage 28 according to the first output voltage E1.

The resistor 29, the variable resistor 30, and the resistor 31 are connected in series between the cathode of the diode 20 and the ground, and one end of the resistor 31 is a comparator 32 as a second comparing means. Is connected to the positive terminal of and the other end is grounded. At the connection point between the resistor 31 and the positive terminal of the comparator stage 32, a second output voltage E2
Detection voltage e2 is generated.

The operation of this circuit having such a configuration will be described. As can be seen from FIG. 1, ON / OFF of the switches S1 and S2 does not affect the operation of this circuit. Power supply terminal 1
When the DC voltage Ein is supplied to the base, the starting current is supplied to the base of the transistor 3 via the resistor 6 to start oscillation, and the secondary voltage 2S and the tertiary winding 2T of the transformer 2 receive the AC voltage Vs and Vt is induced. As a result, when the switches S1 and S2 are turned on, the first and second output voltages E1 and E2 are generated at the output terminals 14 and 24. Note that FIG.
In, there is a relation of E1> E2.

A second detection voltage e2 is generated at one end of the resistor 31 by the second output voltage E2. The comparator stage 32 is the second
Of the detected voltage e2 of the second reference voltage Vref and the voltage of A2 (Vref-e2) are compared with the first reference voltage v
Output as 2. Here, A2 is the amplification degree of the comparator 32. Therefore, v2 = A2 (Vref-e2) ... (1).

The first output voltage E1 produces a first detection voltage e1 at one end of the resistor 27. The comparator 28 compares the first detection voltage e1 with the first reference voltage v2 to obtain A1
The voltage v1 of (e1-v2) is output. Here, A1 is the amplification degree of the comparator 28. Therefore, from the formula (1), v1 = A1 (e1−v2) = A1 ((e1 + A2 · e2) −A2 · Vref) (2)

Equation (2) shows that the output of the comparator 28 has a detection voltage of e1 + A2 · e2 and a reference voltage of A2 · V.
It is equivalent to the case of ref. For example, A1 =
When A2 = 1, v1 = ((e1 + e2) -Vref)
Therefore, the variation Δe1 of the detection voltage e1 and the variation Δe2 of the detection voltage e2 have the same influence on the output voltage v1.

Therefore, the amplification degree A of the second comparator 32
As 2 is made larger than 1, the influence of the variation Δe2 of the detection voltage e2 on v1 becomes large, and the output voltage E2
The control accuracy of is improved. However, if A2 is increased, A1 must be decreased inevitably, and the control accuracy of the output voltage E1 decreases in inverse proportion to the improvement of the control accuracy of the output voltage E2.

On the contrary, the amplification degree A2 of the second comparator 32 is set to 1
The smaller the value, the more the variation Δe2 of the detection voltage e2.
Has a smaller effect on v1 and the control accuracy of the output voltage E2 is reduced, but v1 of the variation Δe1 of the detection voltage e1 is decreased.
The influence on the output voltage E1 is increased, and the control accuracy of the output voltage E1 is improved.

In this way, the voltage control accuracy of the output voltages E1 and E2 differs depending on the amplification degree A2 of the comparator 32, and since E1 and E2 are in inverse proportion to each other in terms of control accuracy, both E1 and E2 have good voltage. The amplification degree A2 is appropriately set so that control accuracy can be obtained.

As described above, this circuit is a control circuit 22 (see FIG. 4) provided separately in the power supply circuit as in the conventional example.
Does not control the DC output voltage by means of, but compares the first and second detection voltages e1 and e2 corresponding to the first and second output voltages E1 and E2 with the first and second reference voltages v2 and Vref. By doing so, the voltage v1 shown in the equation (2) is output from the comparator 28, and the voltage v1 controls the base current IB of the transistor 3, that is, the on / off time ratio of the pulse voltage induced in the transformer 2, and the result First and second
It controls the levels of the output voltages E1 and E2.
The output of the comparator 28 need only be sufficient to drive the transistor 11, and the output of the comparator 32 is the comparator 28.
Is sufficient to drive the comparators 28, 3
In No. 2, power loss occurs only slightly, a heat dissipation plate or the like for heat dissipation is not required unlike the conventional example, and the design cost for heat measures does not occur.

FIG. 2 is a timing chart showing an operation example in this circuit when the output voltage E1 changes due to the load. The dotted line in (A) shows the load fluctuation of the output voltage E1 when feedback control is not performed in this circuit, for example, when the output side of the comparator 28 is disconnected, and (A)
The solid line indicates the fluctuation of the output voltage E1 in this circuit when the same load fluctuation as in the case of the dotted line occurs.

When E1 increases as shown in FIG. 2A, the output voltage v1 of the comparator 28 increases from the equation (2) (see (B)). The voltage v accompanying the rise of the level of the voltage E1
By increasing the level of 1, the level of the induced AC voltage (pulse voltage) of the transformer 2 is controlled to be lower, so that the level of the voltage E2 (see (C)) is lower.
Further, the level of the output voltage v2 of the comparator 32 increases as the level of E2 decreases.

However, since E1 is controlled by v1, as shown in FIG. 2A, the amount of increase is suppressed to a lower level as shown by the solid line, as compared with the case of the dotted line without control. Further, due to the decrease of E2, that is, e2, the output voltage v1 is also suppressed to be lower than the case where only E1 is the control target. This can be understood from the fact that the level of the reference voltage v2 increases due to the level decrease of E2, that is, e2 accompanying the level increase of E1, as shown in the equation (1).

FIG. 3 is a circuit diagram showing another embodiment of the present invention. In the base current control circuit A, the primary side and the secondary side of the transformer 2 are completely electrically separated by a photocoupler. Is. The first detection voltage e1 is the comparator 32
When the output voltage v2 is higher than the output voltage v2, the transistor 33 is turned on, the voltage E2 causes a current to flow in the diode 34a of the photocoupler 34, and the diode 34a emits light. Phototransistor 34b of photocoupler 34
Receives the output light of the diode 34a, a collector current flows according to the amount of received light, that is, the amount of light emitted from the diode 34a, and as a result, the base current IB is controlled. 3
Reference numeral 5 is a collector current limiting resistance of the transistor 33.

In the above embodiment, the case where the present invention is applied to the switching power supply device of the ringing choke converter system is described, but the present invention is not limited to this, and can be applied to the feedforward system, the flyback system, etc.
Has the same effect.

[0055]

As described above, according to the present invention,
Since the first and second output voltages can be controlled in a state where the power loss in the first and second comparison means is minute, a space such as a heat dissipation plate for heat dissipation based on the power loss is not required, and Since there is no need to take design measures against heat dissipation, the design cost can be reduced.

[Brief description of drawings]

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

FIG. 2 is a timing chart for explaining the operation of the circuit of FIG.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional multi-output type switching power supply device.

FIG. 5 is a waveform diagram showing signal waveforms in a multi-output type switching power supply device.

[Explanation of reference numerals] 2 converter transformer 3 transistor 2P primary winding 2S secondary winding 2T tertiary winding 28 comparator (first comparing means) 32 comparator (second comparing means)

Claims (1)

[Claims] 1. A DC power source is connected to a series circuit of a switching element composed of a primary winding of a converter transformer and a transistor, and a first output and a second output are provided to a secondary winding and a tertiary winding of the converter transformer. In a multi-output type switching power supply device to which a rectifying / smoothing circuit for obtaining a voltage is connected, first comparing means for comparing a first detection voltage corresponding to the first output voltage with a first reference voltage, A second comparison means for comparing a second detection voltage corresponding to the second output voltage with a second reference voltage, wherein the first reference voltage is an output voltage of the second comparison means. A multi-output type switching power supply device characterized in that the level of an AC voltage induced in the converter transformer is controlled by the output voltage of the first comparing means.