JP2986981B2 - Multi-output type switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is suitable for use in electronic equipment using a plurality of power supplies having different power supply voltages, particularly two or more power supplies, such as a power supply for a television receiver and a power supply for a video tape recorder. And a multi-output switching power supply.

[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 (two-output) 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. 4, 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, 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. 4 may be manually operated or controlled by a microcomputer.

In the circuit of FIG. 4, only the tertiary winding is shown as the light load winding. However, if a light load winding is required, a quaternary winding, a fifth winding,. .. and an N-th winding can be added.

Next, using the signal waveform diagram of FIG. 5, 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 ( 5H), 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 and the diode 20 connected to the tertiary winding 2T of the transformer 2 (see FIG. 3 illustrates a voltage Vs induced in the secondary winding 2S, and a voltage Vt induced in the tertiary winding 2T.
Also has a different level from the voltage Vs, but has the same waveform as Vs), but no current flows through the diode 12 and the diode 20. 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 collector-emitter voltage VCE 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, the damping 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). 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 increases linearly, 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 stored 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. 5F. 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 flows 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. 5I 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 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 in the positive direction of the rectangular wave voltage VS obtained in the secondary winding 2S of the transformer 2 is reduced (shown in FIG. 9K). 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
The value of the AC voltage induced in the converter transformer 2 changes due to the fluctuation of the base current IB, and the AC voltage Vt generated in the tertiary winding 2T also changes. This change is controlled by the control circuit 22. Then, the control circuit 22 outputs a DC voltage E2 having a constant voltage value.

In this manner, the conventional multi-output type switching power supply shown in FIG. 4 obtains two kinds of stabilized DC power supplies.

[0031]

As described above, the base current and the ON period of the transistor 3 are determined by detecting the output voltage value of the DC power supply having a large capacity or the output voltage value (E1 in FIG. 4) having strict voltage specifications. Was controlled. Therefore, the value of the output voltage Vt of the tertiary winding 2T of the transformer 2 is
This 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 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, 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, a power loss occurs internally, and thus heat is generated. For this reason, a heat radiating plate for heat dissipation is required, and the required space increases. Further, since heat dissipation causes heat rise in the peripheral portion, the peripheral portion must also be designed in consideration of the heat rise, which increases the design cost.

In particular, the fourth winding, the fifth winding,..., N
If the number of power supply circuits having the control circuit 22 such as the next winding increases, the power loss in the multi-output switching power supply increases, so that the necessary space further increases.
In addition, design considerations increase, and the design cost further increases.

The present invention has been made in view of such circumstances, and has as its object to stabilize the output voltage of a light-load power supply circuit without causing power loss.
Therefore, it is an object of the present invention to provide a multi-output switching power supply that does not generate heat dissipation.

[0036]

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. In a multi-output type switching power supply device in which a rectifying and smoothing circuit for obtaining first to (N-1) th output voltages is connected to the secondary winding to the Nth winding, the tertiary winding to the Nth winding are Tightly coupled dummy windings, detecting means for generating a detection voltage corresponding to the first output voltage when the first output voltage is being supplied to the load, and detecting the first output voltage to the load. Dummy voltage detection means for generating a dummy detection voltage corresponding to a dummy voltage obtained by rectifying and smoothing the induced AC voltage of the dummy winding when not supplied, the dummy voltage detection means The level of the induced AC voltage of the converter transformer is controlled by detecting a load variation of any one of the tertiary winding to the Nth winding as a variation of the dummy detection voltage. is there.

[0037]

In the multi-output switching power supply according to the present invention, as shown in FIG. 1, a tertiary winding 2T and a quaternary winding 2F are provided which are tightly coupled to a dummy winding 2D.
T, load fluctuation of the quaternary winding 2F is detected as fluctuation of the induced AC voltage level of the dummy winding 2D, that is, fluctuation of the dummy voltage E1 '.

When the switch S1 is on, that is, when the first
When the output voltage E1 is supplied to the load, the resistor 2
The voltage E1 is applied to the transistor 27 via the variable resistor 5 and the variable resistor 26, the transistor 27 is turned on, and the detection voltage e1 is generated at the connection point between the resistor 28 and the comparator 18.

The comparator 18 outputs a voltage corresponding to the detection voltage e1, controls the base current IB of the transistor 3 via the transistor 11, controls the level of the induced AC voltage of the transformer 2, and outputs the first output. The voltage E1 is controlled.

When the switch S1 is off, that is, when the first
When the output voltage E1 is not supplied to the load, the output terminal 14 is grounded via a load (not shown), so that the transistor 27 is turned off and the transistor 33 is turned on.
A dummy winding 2D is connected to the connection point between the resistor 28 and the comparator 18.
Voltage E obtained by rectifying and smoothing the induced AC voltage of
A dummy detection voltage e2 corresponding to 1 'is generated.

At this time, the dummy winding 2D is connected to the tertiary winding 2
T, because it is in a tightly coupled state with the quaternary winding 2F, the winding 2T,
The level of the induced AC voltage of the dummy winding 2D fluctuates according to the load fluctuation of 2F, and the dummy voltage E1 'and the dummy detection voltage e2 fluctuate.

Thus, the tertiary winding 2T and the quaternary winding 2
F load fluctuation is detected. The comparator 18 outputs a voltage corresponding to the dummy detection voltage e2, controls the base current IB of the transistor 3 via the transistor 11, controls the level of the induced AC voltage of the transformer 2, and controls the dummy voltage E2.
1 ', and indirectly controls the second output voltage E2 and the third output voltage E3.

FIG. 1 shows the case of two windings of the tertiary winding 2T and the quaternary winding 2F. , ... can be increased.

[0044]

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. 4, the same or corresponding parts as those in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, the detecting means ED comprises a transistor 27, resistors 25, 28, 29 and a variable resistor 26.
The resistor 25, the variable resistor 26, the transistor 27 and the resistor 28 are connected in series between the output terminal 14 and the ground, and one end of the resistor 28 is connected to the plus terminal of the comparator 18. , And the other end is grounded. 2
9 is a base current limiting resistor of the transistor 27.

The detecting means DM includes a transistor 33,
It comprises resistors 32, 34, 35, 28, a diode 30, and a capacitor 31. 2D is a dummy winding. One end of the dummy winding 2D is connected to the diode 30 and the capacitor 31 connected in series, and the other end is grounded. A resistor 32 for determining a time constant is connected in parallel to the capacitor 31, one end of the capacitor 31 is connected to the above-described resistor 28 via a transistor 33 and a resistor 34, and the other end is grounded.

Further, 2T is a tertiary winding. One end of the tertiary winding 2T is connected to a diode 36 and a capacitor 37 connected in series, and the other end is grounded. The connection point between the cathode of the diode 36 and one end of the capacitor 37 is connected to the output terminal 24,
Is grounded.

Reference numeral 2F denotes a quaternary winding. One end of the quaternary winding 2F is connected to the diode 38 and the capacitor 39 connected in series, and the other end is grounded. The connection point between the cathode of the diode 38 and one end of the capacitor 39 is connected to the output terminal 40,
Is grounded.

The operation of this circuit having such a configuration when the switch S1 is turned on, that is, when the first output voltage E1 is supplied to the load 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 oscillation is started, and the secondary winding 2S and the dummy winding 2 of the transformer 2 are started.
D, the AC voltage Vs applied to the tertiary winding 2T and the quaternary winding 2F,
Vd, Vt and Vf are induced. Thereby, the output terminal 14, the cathode of the diode 30 and the transistor 3
A first output voltage E1, a dummy voltage E1 ', a second output voltage E2, and a third output voltage E3 are generated at the connection point with the emitter No. 3, the output terminal 24 and the output terminal 40.

At this time, since the switch S1 is on, the voltage E1 is applied to the transistor 27 via the resistor 25 and the variable resistor 26, and the transistor 27 is turned on. A detection voltage e1 is generated at the connection point.

The comparator 18 compares the detection voltage e1 with Vref, outputs a voltage corresponding to the voltage e1, and controls the base current IB of the transistor 3 via the transistor 11. Thus, the level of the induced AC voltage of the transformer 2 is controlled, and the first output voltage E1 is kept constant.

Therefore, the load fluctuation of the first output voltage E1 results in the fluctuation of the detection voltage e1 and the fluctuation of the output voltage of the comparator 18. The level of the induced AC voltage of the transformer 2 is controlled by the output voltage of the comparator 18 so that the first output voltage E1 becomes constant. The value itself of the first output voltage E1 can be adjusted by the variable resistor 26,
It is adjusted to be an appropriate value when 1 is supplied to the load.

The number of turns of the windings 2T and 2F is determined by the voltages E2 and E3.
Is adjusted after the adjustment of the variable resistor 26 so as to have an appropriate value.

Next, the operation of this circuit when the switch S1 is off, that is, when the first output voltage E1 is not supplied to the load, will be described. When the switch S1 is off, the output terminal 14 is grounded via a load (not shown), so that no voltage is applied to the transistor 27 and the transistor 27 is off.

Since the base of the transistor 33 is at zero potential via the resistor 35, the transistor 33 is turned on by the dummy voltage E1 '. As a result, a dummy detection voltage e2 corresponding to the dummy voltage E1 'is generated at the connection point between the resistor 34 and the resistor 28 via the transistor 33 and the resistor 34.

The comparator 18 compares the dummy detection voltage e2 with the reference voltage Vref, outputs a voltage corresponding to the voltage e2, and controls the base current IB of the transistor 3 via the transistor 11.

In this circuit, the winding 2D is a winding 2T,
Because of the tight coupling with the second winding 2F, the load fluctuation in the windings 2T and 2F appears as a fluctuation of the dummy voltage E1 '. For example, when the output current of the winding 2T decreases due to a lighter load, the level of the induced AC voltage Vt increases,
As the level of Vt rises, other induced AC voltages Vd,
The level of Vf also increases. An increase in the level of Vd results in an increase in the level of the dummy voltage E1 '. As a result, the base current IB decreases, and the level of the induced AC voltage of the transformer 2 drops, so that the levels of Vd, Vt, and Vf are maintained at constant values.

FIG. 2 shows a configuration example in which the winding 2D and the windings 2T and 2F are tightly coupled. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and 41 is a core. As described above, by sandwiching the dummy winding 2D between the tertiary winding 2T and the quaternary winding 2F in a sandwich shape, tight coupling can be easily achieved. Of course, these three members can also be tightly coupled by bifilar winding.

In this circuit, two windings of the tertiary winding 2T and the quaternary winding 2F are shown as the windings for the light load. , A fifth winding, a sixth winding,..., An N-th winding.

As described above, in this circuit, the transistors 27 and 33 are alternately turned on and off, and the level of the induced AC voltage of the transformer 2 is controlled according to the detection voltage e1 or the dummy detection voltage e2. Therefore, no power loss occurs in the transistors 27 and 33, and the comparator 18 only needs to drive the transistor 11, so that the power loss is very small.

As described above, in the present circuit, the power loss is minute, and the space for the heat radiating plate and the like required in the conventional circuit is not required, and the measure for heat dissipation is not required. Cost is reduced.

FIG. 3 is a circuit diagram showing another embodiment of the present invention. In the base current control circuit A, the primary and secondary sides of the transformer 2 are completely electrically separated by a photocoupler. It is. When the detection voltage e1 or the dummy detection voltage e2 is higher than the reference voltage Vref of the reference power supply 18a, the transistor 41 is turned on and the voltage E
2, a current flows through the diode 42a of the photocoupler 42, and the diode 42a emits light. Photo coupler 42
The phototransistor 42b receives the output light of the diode 42a, and the collector current flows according to the amount of received light, that is, the amount of light emitted by the diode 42a, and as a result, the base current IB is controlled. Reference numeral 43 denotes a collector current limiting resistor of the transistor 41.

In the above embodiment, the case where the present invention is applied to a ringing choke converter type switching power supply device has been described. However, the present invention is not limited to this, and can be applied to a feed forward type, a flyback type, and the like.
A similar effect is achieved.

[0064]

As described above, according to the present invention,
Since the level of the induced AC voltage of the converter transformer is controlled by the detection voltage and the dummy detection voltage, the power loss is very small, eliminating the need for a space for a heatsink and the like required in the conventional circuit. Since there is no need to take measures against radiation, there is an effect that the design cost is reduced.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram showing a configuration example of a winding of the circuit of FIG. 1;

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 the multi-output switching power supply device.

[Explanation of symbols]

 2 Converter transformer 3 Transistor 2P Primary winding 2S Secondary winding 2T Tertiary winding 2F Quaternary winding 2D Dummy winding ED detecting means DM Dummy voltage detecting means

Claims (1)

(57) [Claims] 1. 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 secondary winding to an N-th winding of the converter transformer have first to (N) th windings. -1) a multi-output switching power supply to which a rectifying / smoothing circuit for obtaining an output voltage is connected, a dummy winding tightly coupled to the tertiary winding to the N-th winding;
Detecting means for generating a detection voltage corresponding to the first output voltage when the first output voltage is supplied to the load; and the dummy winding when the first output voltage is not supplied to the load And a dummy voltage detecting means for generating a dummy detection voltage corresponding to a dummy voltage obtained by rectifying and smoothing the induced AC voltage of the above-mentioned AC voltage. A multi-output type switching power supply device, wherein a level of an induced AC voltage of the converter transformer is controlled by detecting a load fluctuation of any one of the windings as a fluctuation of the dummy detection voltage.