JPH11332235A - Multiple-output switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a multiple-output switching power supply device as a large capacity power supply by reducing the inclination of a current waveform flowing to a parasitic inductance and reducing the voltage drop. SOLUTION: When a main switch element 2 is ON, a primary coil 3a of a transformer 3 accumulates energy. On the other hand, when the main switch element 2 is OFF, energy is released from secondary coils 3b and 3c of the transformer 3 to output. In a secondary current limiter circuit 16 for suppressing the increase rate of the waveform of a current that flows to a secondary circuit when the main switch element 2 is OFF is turned, a series circuit consisting of a sub switch element 4 and a capacitor 5 that is turned on and off when the main switch element 2 is ON and OFF, respectively, is connected in parallel with the transformer primary coil 3a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-output switching power supply for supplying a stabilized DC voltage to industrial and consumer electronic equipment.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional multi-output switching power supply device, in which the circuit of a flyback converter of a plus / minus output type (bipolar output type) is simplified as an example. The primary circuit of this flyback converter has a primary winding 3a of a transformer 3 and a main switch element 2 using a MOS-FET or the like connected in series, and the secondary circuit has two secondary windings 3b of the transformer 3. , 3c is provided with a rectifier circuit composed of rectifier diodes 8, 9 and smoothing capacitors 10, 11, respectively, to take out a plus output terminal 14p, a common output terminal 14c, and a minus output terminal 14n.

The main switch element 2 is a composite voltage (Vout1 + Vout2) of the output voltages Vout1 and Vout2 of the two rectifier circuits.
Is detected by the error amplifier 12 and monitored by the drive circuit 13, and the ON period of the main switch element 2 is controlled so that the combined output voltage becomes a specified voltage. The operation of the flyback converter is as follows. When the main switch 2 is turned on, a current flows from the input voltage source 1 to the primary winding 3a of the transformer 3 to store energy in the transformer 3, and when the main switch element 2 is turned off, the secondary winding is turned off. Energy is supplied to the output from lines 3b, 3c through rectifier diodes 8,9.

[0004]

However, in such a conventional multi-output switching power supply, for example, when a load is connected to the plus output terminal 14p and the common output terminal 14c to allow current to flow only on one side, or When the plus output terminal 14p, the common output terminal 14c, and the minus output terminal 14n are connected to a load and an imbalance occurs in the output current, the parasitic inductance 6, which is a combination of the parasitic inductance such as the leakage inductance of the transformer 3 and the circuit pattern, is used. 7, the output voltage on the side where no current is flowing or on which the current is low increases, and the output voltage on the side where current is flowing or on which the current is high decreases, and the output voltage fluctuates. Becomes larger.

FIG. 6 shows a current waveform of the secondary windings 3b and 3c of the transformer 3 flowing in synchronization with the turning off of the main switch element 2. Here, assuming that the value of the parasitic inductance obtained by combining the leakage inductance of the transformer 3 and the parasitic inductance depending on the circuit pattern and the like is Le, the voltage drop Ve generated by the parasitic inductance Le is expressed by the following equation. Ve = Le × (di / dt) (1) where, Le: a composite value of the leakage inductance of the transformer and a parasitic inductance such as a pattern Ve: a voltage drop generated by the composite parasitic inductance Le di / dt: flows through the composite parasitic inductance Le From the equation (1), the voltage drop Ve generated by the parasitic inductance Le depends on the gradient of the current waveform. When the switch element 2 is off, the transformer secondary Since the current waveform of the side current i sharply rises, (di / dt) increases, and the voltage drop Ve of the combined parasitic inductance Le increases.

FIG. 7 shows the relationship between output current and output voltage in the flyback converter of FIG. The drive circuit 13 of FIG. 5 uses the error amplifier 12 to output two output voltages Vout1 and Vout1.
The combined voltage (Vout1 + Vout2) of out2 is detected, and the ON period of the main switch element 2 is controlled so as to become a specified voltage. Here, a case where the output voltage Vout1 is high and the output voltage Vout2 is low is taken as an example.

The output current Iout1 is a current flowing out of the load, and the output current Iout2 is a current flowing out of the load. Even if the output currents Iout1 and Iout2 become unbalanced, Iout1
And Iout2 flows to some extent, the output voltage Vout
1, Vout2 hardly fluctuates. However, the output current Io
Unbalance occurs in ut1 and Iout2, and Iout1 or Io
When the current of ut2 is smaller than a certain current value, the output on the light load side peak-holds the voltage drop Ve of the parasitic inductance Le.

At this time, the output voltage Vout1 with the smaller current rises due to the fluctuation due to the voltage drop generated by the combined parasitic inductances 6 and 7 that combine the parasitic inductance such as the leakage inductance of the transformer 3 and the circuit pattern, and the combined output voltage In order to keep (Vout + Vout2) constant, the output voltage Vout2 having a large current decreases, and each output voltage Vou
The fluctuations of t1 and Vout2 increase.

Since the voltage drop Ve of the parasitic inductances 6 and 7 causing such output voltage fluctuations increases as the output current increases, it can be used only for a small-capacity power supply of about several tens of watts. Can not. The present invention provides a multi-output switching power supply that can be used as a large-capacity power supply by reducing a voltage drop due to a parasitic inductance of a transformer secondary-side circuit when an imbalance occurs in an output current, suppressing a change in output voltage. The purpose is to:

[0010]

In order to achieve this object, the present invention is configured as follows. First, the present invention relates to a primary circuit in which a primary winding of a transformer and a main switch element are connected in series to an input DC power supply, a plurality of secondary windings of the transformer are connected in series, and rectification and smoothing are performed for each secondary winding. A secondary circuit for providing and outputting a circuit; and a drive circuit for monitoring the combined voltage of the output voltages of the rectifier circuits and controlling the ON period of the main switch element. A multi-output switching power supply device that stores energy in a winding and discharges energy from a secondary winding of a transformer to an output when a main switch element is turned off.

In the multi-output switching power supply device according to the present invention, a secondary current suppressing circuit for suppressing an increase rate of a current waveform flowing in the secondary circuit when the main switch element is turned off is provided. . This secondary current suppression circuit is characterized in that a series circuit of a sub-switch element and a capacitor which is turned off when the main switch element is turned on and turned on when the main switch element is turned off is connected in parallel with the primary winding of the transformer. .

A secondary current suppressing circuit according to another aspect of the present invention includes a series circuit of a sub-switch element and a capacitor, which is turned off when the main switch element is turned on and turned on when the main switch element is turned off, by the driving circuit. The switching element is connected in parallel. According to such a multi-output switching power supply device of the present invention, when the main switch element is turned off and the energy stored in the transformer is released to the secondary side, the sub-switch element is turned on and the capacitor for clamping is charged. By discharging, the slope of the current waveform flowing to the secondary side is reduced, and the effect of the voltage drop that occurs on the parasitic inductance is almost eliminated, so that a stable output voltage can be obtained even if an imbalance occurs in the output current. .

As described above, even if the output current is unbalanced, the output voltage hardly fluctuates, so that it can be used for a multi-output power supply up to several hundred watts.

[0014]

FIG. 1 shows a first embodiment of a multi-output switching power supply according to the present invention, taking a flyback converter of a plus / minus output type as an example.
In FIG. 1, a flyback converter of a plus / minus output type serving as a multi-output switching power supply device of the present invention has a transformer 3 connected to an input DC power supply 1 as a primary side circuit.
The primary winding 3a and the main switch element 2 using a MOS-FET or the like are connected in series. The secondary circuit of the flyback converter includes two secondary windings 3 provided in the transformer 3.
b, 3c are connected in series with a midpoint tap, the midpoint tap is connected to a common output terminal 14c, and rectifier diodes 8, 9 and smoothing capacitors 10, 1 are connected to the secondary windings 3b, 3c.
1 are connected to each other to form a rectifier circuit.

The switching of the main switch element 2 is performed by a drive circuit 13, and the drive circuit 13 outputs the output voltages Vout1, Vout2 of the secondary windings 3b, 3c detected by the error amplifier 12.
(Vout1 + Vout2). That is,
One of the error amplifiers 12 is connected to the plus output terminal 14p, and the other is connected to the minus output terminal 14n. The drive circuit 13 controls the ON period in the ON / OFF control of the main switch element 2 so that the composite voltage (Vout1 + Vout2) detected by the error amplifier 12 becomes a specified constant voltage.

In the present invention, a secondary current suppressing circuit 16 is newly provided in the primary circuit for such a plus / minus output flyback converter. The secondary current suppression circuit 16 connects a series circuit of the sub-switch element 4 and the clamp capacitor 5 in parallel with the primary winding 3a of the transformer 3. The sub-switch element 4 is turned on / off by a control signal E2 from the drive circuit 13. That is,
The sub-switch element 4 is turned off when the main switch element 2 is on, and turned on when the main switch element 2 is off. Therefore, the control signal E2 from the drive circuit 13 for the sub-switch element 4 becomes an inverted signal of the control signal E1 for the main switch element 2.

Next, the operation of the first embodiment shown in FIG. 1 will be described. The drive circuit 13 controls the ON / OFF control of the main switch element 2 so that the composite voltage (Vout1 + Vout2) on the output side detected by the error amplifier 12 becomes a constant voltage. Is output. When the main switch element 2 is on, the input DC power supply 1
Current flows through the primary winding 3a, and energy is stored in the transformer 3.

When the main switch element 2 is off, the energy stored in the transformer 3 is released from the secondary windings 3b and 3c through the rectifier diodes 8 and 9, respectively, and is smoothed by the smoothing capacitors 10 and 11. At the same time, the power is supplied to the load connected to the output terminals 14p, 14c, and 14n. Here, in the secondary circuit of the transformer 3, parasitic inductances 6 and 7 due to the leakage inductance of the transformer 3 and the inductance of the circuit pattern and the like are present as shown in the figure. Therefore, when the main switch element 2 is turned off and the energy is released from the transformer 3, the current flowing through the secondary windings 3 b and 3 c passes through the parasitic inductances 6 and 7, causing a voltage drop.

At this time, the voltage drop of the parasitic inductances 6 and 7 is proportional to the value Le of the parasitic inductances 6 and 7 and the gradient (di / dt) of the current waveform as shown in the above equation (1). In order to suppress the fluctuation of the output voltage due to the parasitic inductances 6 and 7 existing in the secondary circuit of the transformer 3, a secondary current suppression circuit 16 is provided in the primary circuit.

When the secondary current suppressing circuit 16 stores energy in the transformer 3 in which the main switch element 2 is on, the sub switch element 4 is turned off and stops operating. When the main switch element 2 is turned off and energy is discharged from the transformer 3 to the output, the sub switch element 4 is turned on at this time. When the sub-switch element 4 is turned on, the clamp capacitor 5 due to the energy stored in the transformer 3
And discharge of energy to the secondary side of the transformer 3 is suppressed.

For this reason, the gradient (di / dt) of the increase in the current waveform flowing through the secondary windings 3b and 3c of the transformer 3 when the main switch element 2 is turned off is reduced, and this is given by the equation (1). The voltage drop of the parasitic inductances 6 and 7 can be reduced. FIG. 2 is a first view of FIG.
The current waveform of the secondary current i of the transformer 3 accompanying the on / off of the main switch element 2 in the embodiment is shown, the solid line is the current waveform according to the present invention, and the broken line is the conventional current waveform.

As is apparent from the current waveform of the secondary current i of the transformer 3, in the first embodiment shown in FIG.
By providing the secondary current suppressing circuit 16 that turns on when the main switch element 2 is turned off and connects the clamp capacitor 5 in parallel with the primary winding 3a of the transformer 3, the current i flowing through the secondary side of the transformer 3 at this time is reduced. Current waveform slope (di / dt)
Can be made sufficiently smaller than the conventional example indicated by the broken line, and as a result, the voltage drop occurring in the parasitic inductances 6 and 7 can be greatly reduced.

As described above, when the voltage drop at the parasitic inductances 6 and 7 existing on the secondary side of the transformer 3 can be greatly reduced, the positive output terminal 14p and the common terminal 14c and the negative output terminal 14n and the common terminal 14c Even if the current balance between the output currents Iout1 and Iout2 with respect to the load connected to the load is lost, since the voltage drops of the parasitic inductances 6 and 7 are greatly reduced, the output voltages Vout1 and Vout2 due to this are reduced. It can be suppressed to a state where there is almost no fluctuation.

Thus, as shown in FIG.
Is output in a region where the output current Iout1 is small even if the error amplifier 12 detects the combined voltage (Vout1 + Vout2) of the two output voltages Vout1 and Vout2 and controls the ON period of the main switch element 2 so as to be constant. Even if a current imbalance occurs with the current Iout2, the output voltage Vou
There is no change in t1 and Vout2, and what has conventionally fluctuated as shown by the broken line can be kept almost constant as shown by the solid line.

Therefore, since the output voltage does not fluctuate when the current balance is lost due to the voltage drop of the parasitic inductances 6 and 7 of the secondary circuit, only a small capacity of about several tens of watts can be realized conventionally. There was no plus in Figure 1
The capacity of the negative output type flyback converter can be expanded to a multi-output switching power supply of up to about several hundred watts.

FIG. 4 shows a second embodiment of a multi-output switching power supply according to the present invention.
A flyback converter of plus / minus output type is taken as an example. In the second embodiment of FIG. 4, the flyback converter has a primary side circuit in which a primary winding 3a of a transformer 3 and a main switch element 2 are connected in series to an input DC power supply 1, as in the embodiment of FIG. The secondary side circuit connects the smoothing capacitors 10 and 11 to the secondary windings 3b and 3c of the transformer 3 via the rectifier diodes 8 and 9 to provide a plus output terminal 14p and a common output terminal 1 for multiple outputs.
4c and a negative output terminal 14n.

Further, the combined voltage (Vout1 + Vout2) of the output is detected by the error amplifier 12, and the drive circuit 13 controls the ON period in the on / off control of the main switch element 2 so that the combined voltage (Vout1 + Vout2) becomes a constant voltage. doing. For such a flyback converter,
In the second embodiment, a secondary current suppression circuit 16 is provided in parallel with the main switch element 2. That is, the secondary current suppression circuit 16 connects a series circuit of the sub-switch element 4 and the clamp capacitor 5 in parallel with the main switch element 2. The control signal E2 obtained by inverting the control signal E1 of the main switch element 2 is supplied to the sub switch element 4. When the main switch element 2 is on, the sub switch element 4 is off and the main switch element 2 is off. At this time, the sub-switch element 4 is turned on.

In the second embodiment shown in FIG. 4, when the main switch element 2 is turned off and the energy stored in the transformer 3 is released to the secondary side, the sub switch element 4 is turned on and the transformer 3 is turned on. The clamp capacitor 5 is charged / discharged with the energy accumulated in the secondary winding 3b, 3c of the transformer 3 due to the charging / discharging of the clamp capacitor 5, and the increase or gradient of the current flowing through the secondary winding 3b of the transformer 3 in FIG. As compared with the conventional current waveform indicated by the broken line as in the current waveform indicated by the solid line i, the voltage drop occurring in the parasitic inductances 6 and 7 existing on the secondary side is greatly reduced.

Even if the output currents Iout1 and Iout2 are imbalanced by such a drastic reduction of the voltage drop of the parasitic inductances 6 and 7 by the secondary current suppression circuit 16, the output voltages Vout1 and Vout2 are almost completely reduced. The characteristics as shown by the solid line in FIG. 3 can be obtained without variation, and as a result, the device can be used as a multi-output switching power supply up to about several hundred watts.

In the above embodiment, a two-output switching power supply device that outputs a plus output and a minus output is taken as an example. However, an arbitrary output can be obtained by increasing the number of secondary circuits for the transformer 3 by a plurality of systems. It can be a number. In addition, the present invention is not limited to the above embodiments, and includes appropriate modifications without impairing the objects and advantages.

[0031]

As described above, according to the present invention, when the main switch element is turned off and the energy stored in the transformer is released to the secondary side, the sub switch element is turned on to reduce the energy of the transformer. By charging / discharging the clamp capacitor, the gradient (increase rate) of the current waveform flowing to the secondary side is reduced, and the voltage drop generated in the parasitic inductance generated on the secondary side is reduced. Even if the output current is unbalanced, the output voltage hardly fluctuates, thereby expanding the power supply capacity from the limit of several tens of watts to a multi-output switching power supply of several hundred watts. be able to.

[Brief description of the drawings]

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

FIG. 2 is a time chart of a transformer secondary-side current waveform accompanying turning on / off of a main switch element in FIG. 1;

FIG. 3 is a characteristic diagram of a load and an output voltage in FIG. 1;

FIG. 4 is a circuit diagram of a second embodiment of the present invention.

FIG. 5 is a circuit diagram of a conventional device.

6 is a time chart of a transformer secondary-side current waveform associated with turning on / off a main switch element in the conventional device of FIG. 5;

7 is a characteristic diagram of a load and an output voltage in the conventional device of FIG.

[Explanation of symbols]

 1: Input DC power supply 2: Main switch element 3: Transformer 3a: Primary winding 3b, 3c: Secondary winding 4: Sub-switch element 5: Clamp capacitor 6, 7: Parasitic inductance 8, 9: Rectifying diode 10, 11 : Smoothing capacitor 12: Error amplifier 13: Control drive circuit 14 p: Positive output terminal 14 c: Common output terminal 14 n: Negative output terminal 16: Secondary current suppression circuit

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[Procedure amendment]

[Submission date] May 19, 1998

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4

Claims (3)

[Claims] 1. A primary circuit in which a primary winding of a transformer and a main switch element are connected in series to an input DC power supply, a plurality of secondary windings of the transformer are connected in series, and rectification is performed for each secondary winding. A secondary circuit for providing a smoothing circuit for output, and a drive circuit for monitoring a combined voltage of the output voltages of the rectifier circuits and controlling an ON period of the main switch element, wherein the main switch element is turned on. In a multi-output switching power supply device that stores energy in the primary winding of the transformer and discharges energy from the secondary winding of the transformer to the output when the main switch element is off, when the main switch element is off. A multi-output switching power supply device comprising a secondary current suppressing circuit for suppressing an increase rate of a current waveform flowing in the secondary circuit. 2. The multi-output switching power supply according to claim 1, wherein the secondary current suppressing circuit is turned off when the main switching element is turned on by the driving circuit, and is turned on when the main switching element is turned off. A multi-output switching power supply, wherein a series circuit of a sub-switch element and a capacitor is connected in parallel with a primary winding of the transformer. 3. The multi-output switching power supply according to claim 1, wherein the secondary current suppressing circuit is turned off when the main switch element is turned on by the drive circuit, and is turned on when the main switch element is turned off. A multi-output switching power supply device, wherein a series circuit of a sub-switch and a capacitor is connected in parallel with the main switch element.