JPH11252911A - Composite output switching power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of short-circuit current of output rectifier elements and improve efficiency in a composite output switching power unit outputting a plurality of output voltages, by using a magnetic amplifier circuit or the like using a saturable reactor. SOLUTION: As a forward system, this power unit is at least provided with an output circuit which switches an input voltage by switching operation controlling the on/off time of a main switch (main switching element) Q1, supplies the voltage to the primary side of a transformer T0, uses a magnetic amplifier circuit on the secondary side of the transformer T0 and output rectifier elements Q1, Q2 on the forward side and the wheel side, and obtains a rectified output. In this case, the on-state of a main switch Q1 is detected from the output of the magnetic amplifier circuit by an output rectifier element control circuit 4. An off signal which turns on the output rectifier element Q3 on the flywheel side prior to the on-time of the output rectifier element Q2 on the forward side is supplied to the output rectifier element Q3 on the flywheel side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite output switching power supply, and more particularly, to a composite output switching power supply with high efficiency.

[0002]

2. Description of the Related Art Conventionally, synchronous rectification has been studied as a measure for improving the efficiency of a forward switching power supply.

For example, a synchronous rectification type switching power supply device shown in FIG. 4 is a typical example.

That is, in the switching power supply device shown in FIG. 4, a DC (Vin) voltage from the power supply 1 is controlled by a PWM (pulse width modulation) control section 21 at a predetermined timing to control the gate of the main switching element (hereinafter referred to as “main switching element”). The switch is switched by Q11, supplied to the primary side of the transformer T, and the pulse voltage (VT) induced on the secondary side of the transformer T is rectified by the diode D11 on the forward side and the diode D12 on the flywheel side. , And a main winding L11 of a smoothing inductor L and a smoothing capacitor C0.
, And is applied to the load R as a predetermined DC voltage.

The DC voltage applied to the load R is fed back to the PWM control unit 21 by a feedback circuit including a resistor R10, a photocoupler PH1, and a Zener diode (Zener voltage VZ) ZD. The drive of the gate of the main switch Q11 is controlled by a predetermined timing by the switch 21 so that the main switch Q11 is switched.

[0006] The photocoupler PH1 has a light emitting diode PD and a phototransistor PT0.

Further, the switching power supply uses or substitutes a diode D12 auxiliary switching element (hereinafter referred to as "auxiliary switch") Q12 on the flywheel side.

The driving signal for the gate of the auxiliary switch Q12 is obtained by supplying the induced voltage of the auxiliary winding L12 of the inductor L to the gate.

According to the switching power supply device, the diode D12 on the flywheel side on the secondary side of the transformer T
Is replaced by an auxiliary switch Q12 composed of a MOSFET, it is possible in principle to reduce the forward voltage drop (0.5 V with a Schottky barrier diode) inevitable in the diode D12 as much as possible.

[0010]

However, in the above-described conventional switching power supply, neither the ON time nor the OFF time of the main switch Q11 is constant.

Therefore, in order to replace the flywheel-side diode D12 (cathode-anode voltage VK-A) and the forward-side diode D11 with an element such as an auxiliary switch Q12 composed of a MOSFET, this element must be replaced by a transformer T. The drive is performed using the winding voltage, the winding voltage of the inductor L, or the drive signal of the gate of the main switch Q11.

One example of realizing this with a simple driving circuit is a circuit configuration as shown in FIG. 4, but the problem in this case is that as shown in FIG. 5, the main switch Q11 is turned on and the diode D11 is turned on. Is the same as the timing at which the switch starts conducting and the timing at which the drive signal (VG-S) of the gate of the auxiliary switch Q12 falls.

The auxiliary switch Q12 cannot be turned off immediately even when the gate drive signal falls.
Therefore, immediately after the main switch Q11 is turned on, the auxiliary switch Q12 is still in the on state. As a result, a large short-circuit current Ik flows through the diode D11 and the auxiliary switch Q12 as shown in FIG. Will be lost.

Further, recently, a composite output switching power supply which can supply a plurality of output voltages to a load by using a mag-amp circuit using a saturable reactor has been put to practical use. There is also a demand for a device to prevent short-circuit current from occurring and to improve efficiency.

The present invention has been made in view of the above circumstances, and in a composite output switching power supply device capable of supplying a plurality of output voltages to a load using a mag amplifier circuit using a saturable reactor, It is an object of the present invention to prevent short-circuit current from being generated from an output rectifying element to an output rectifying element on the flywheel side and to improve efficiency.

[0016]

According to the first aspect of the present invention,
The input voltage is switched by the switching operation that controls the ON and OFF times of the main switch and supplied to the primary side of the transformer.The secondary side of the transformer has a mag amplifier circuit and output rectifiers on the forward and flywheel sides. In the composite output switching power supply of the forward type, at least comprising an output circuit that obtains a rectified output using the same, detects the ON state of the main switch from the output of the mag amplifier circuit, and sets the output rectifying element on the flywheel side to the forward side. An output rectifying element control circuit for supplying an off signal for turning off the output rectifying element before the on time of the output rectifying element to the output rectifying element on the flywheel side is provided.

According to the present invention, the output rectifier control circuit detects the ON state of the main switch from the output of the mag amplifier circuit provided on the secondary side of the transformer, and switches the flywheel output rectifier to the forward side. Since the off signal for turning off the output rectifying element is supplied to the flywheel side output rectifying element before the on time of the output rectifying element, the flywheel output rectifying element is turned on when the forward side output rectifying element is turned on. The elements are always turned off, thereby reliably preventing short-circuit current from flowing between the rectifier on the forward side and the rectifier on the flywheel side, and improving the efficiency of this combined output switching power supply. it can.

According to a second aspect of the present invention, the input voltage is switched by a switching operation for controlling the on / off time of the main switch and supplied to the primary side of the transformer.
On the secondary side of the transformer, a first output circuit that obtains a rectified output using forward and flywheel output rectifiers, a mag amplifier circuit, and a forward and flywheel output rectifier are used. And a second output circuit having a rectifier circuit for obtaining a rectified output.
Is connected to the connection point of the output rectifying element on the forward side and the flywheel side of the output circuit, and detects the ON state of the main switch from the output of the output rectifying element on the forward side and the flywheel side. An output rectifying element control circuit that supplies an off signal for turning off the flywheel side output rectifying element before the forward side output rectifying element is turned on to the flywheel side output rectifying element in the second output circuit; It is characterized by the following.

According to the present invention, the ON state of the main switch is detected by the output rectifier control circuit from the outputs of the forward rectifier and the flywheel output rectifier of the first output circuit. An off signal for turning off the flywheel output rectifier in the output circuit before the forward output rectifier is turned on is supplied to the flywheel output rectifier in the second output circuit. Therefore, at the time when the forward-side output rectifier in the second output circuit is turned on, the flywheel-side output rectifier is always turned off, whereby the forward-side rectifier and the flywheel-side output rectifier are turned off. It is possible to reliably prevent short-circuit current from flowing between the rectifier elements, and to improve the efficiency of this composite output switching power supply. That.

[0020]

Embodiments of the present invention will be described below in detail.

(Embodiment 1) FIG. 1 shows a composite output switching power supply unit according to Embodiment 1 of the present invention. In the forward system, a first side is provided on the secondary side of a transformer T0.
A first output circuit for outputting the output V1 of the
And a second output circuit for outputting 2.

In this composite output switching power supply, a main switching element (hereinafter referred to as a "main switch") whose gate is driven and controlled at a predetermined timing by a PWM (pulse width modulation) control unit 2 with a DC voltage Vin from a power supply 1 is used. ) Q
1 to switch the primary winding N of the transformer T0.
The pulse voltage VT1 supplied to P1 and induced in the first secondary winding nS1 of the transformer T0 is rectified by a forward-side diode D5 and a flywheel-side diode D6 in the first output circuit. Inductor L3
And a smoothing capacitor C3 for smoothing and supplying the first output (DC voltage) V1 to the load R01.

The output V1 applied to the load R01 is fed back to the PWM control unit 2 by an output voltage feedback circuit 3 and a feedback circuit including a photocoupler PH1 similar to the conventional example. Drive control of the gate of the main switch Q1 at a predetermined timing, thereby causing the main switch Q1 to perform a switching operation, and
1 is to be stabilized.

In FIG. 1, a reset diode D1 is connected between the primary winding NP of the transformer T0, the series winding auxiliary winding nh, and the negative electrode of the power supply 1.

The photocoupler PH1 has a light emitting diode PD and a phototransistor PT00.

The second output circuit for outputting the second output V2 in the composite output switching power supply device comprises:
The pulse voltage VT2 induced in the second secondary winding nS2 of the transformer T0 is converted into a mag-amp circuit using a saturable reactor L1, an output rectifier Q2 using a MOSFET on the forward side, and an output using a MOSFET on the flywheel side. The current is rectified by the rectifying element Q3, further smoothed by the smoothing inductor L2 and the smoothing capacitor C2, and supplied to the load R02 as a predetermined second output (DC voltage) V2 (output current I02).

The second output circuit includes an output rectifier control circuit 4 for controlling the output rectifier Q3 on the flywheel side, and an output control circuit 5 for stabilizing and controlling the second output V2. Is provided.

The output rectifier Q2 on the forward side of the second output circuit supplies a gate drive signal by supplying the winding voltage of the second secondary winding nS2 of the transformer T0 via the resistor R2. Has become. Further, a diode D7 is connected in parallel with the source-drain of the output rectifier Q3 on the flywheel side. In FIG. 1, the output rectifier Q3 on the flywheel side has a parasitic capacitance C1 indicated by a dotted line between its source and gate.

The output rectifying element control circuit 4 includes a resistor R1 connected in series between the winding end terminal of the second secondary winding nS2 of the transformer T0 and the gate of the output rectifying element Q3 on the flywheel side. A series circuit of a diode D4 and a resistor R6, and the inverting input terminal is a forward side output rectifier Q
2 and the non-inverting input terminal is connected to the resistor R1.
, The comparator IC2 connected to the connection point of the diode D4
A resistor R4 connected between the non-inverting input terminal and the output terminal of the comparator IC2, and a diode D3 connected in series between the output terminal of the comparator IC2 and the gate of the output rectifier Q3 on the flywheel side. , And a series circuit of a resistor R5.

The comparator IC2 has a positive voltage V
+, Minus voltage V- is supplied.

The output control circuit 5 includes resistors R8 and R9 for dividing the second output V2 of the second output circuit, a reference voltage source (reference voltage Vref) E0, and a divided voltage by resistors R8 and R9. And a reference voltage Vref, and a comparator I which outputs a drive signal from an output terminal when the output V2 drops.
The base is connected to C1 and the output terminal of the comparator IC1 via a resistor R7, the emitter is grounded, and the collector is connected to a diode D2 and a resistor R3.
And a transistor Q4 connected to a connection point between the output side and the drain of the output rectifier element Q2 on the forward side.

Next, the operation of the composite output switching power supply having the above-described configuration will be described with reference to the timing charts of the waveforms of the respective parts shown in FIG.

The first of this composite output switching power supply device
In the output circuit, the first output voltage V1 applied to the load R01 is fed back to the primary side via the photocoupler PH1 by the output voltage feedback circuit 3, and the gate of the main switch Q1 is switched by the PWM control unit 2 to PWM. By controlling, the first output V1 is stabilized.

On the other hand, the second output circuit employs a circuit configuration using a supersaturated reactor L1 constituting the mag amplifier circuit, and has a MOSF having an operation waveform shown in FIG.
D of output rectifier Q3 on flywheel side using ET
As shown by the voltage waveform between -S, this output rectifier element Q3
Is shortened by an amount corresponding to the time t shown in FIG. 2 by the mag amplifier circuit to stabilize the output V2 of the second output circuit.

That is, in FIG. 2, as shown by the voltage waveform between DS of the forward-side output rectifier element Q2, the exciting inductor component of the transformer T0 is reset while the main switch Q1 is off. Period T2 shown in FIG.
(The second secondary winding ns2 of the transformer T0 of the output control circuit 5)
During the period in which the pulse voltage VT2 induced in the output control circuit 5 is negative), the comparator IC1 of the output control circuit 5 outputs a drive signal from the output terminal according to the decrease of the output V2,
When the transistor Q4 is turned on, the supersaturated reactor L1
VsL (= T2 × nS2 × Vin /
(T × nP)), thereby stabilizing the output V2 of the second output circuit.

The output rectifier Q2 on the forward side using the MOSFET of the second output circuit is the second output rectifier Q2 of the transformer T0.
The gate drive signal is obtained by supplying the winding voltage of the secondary winding nS2 through the resistor R2. However, it is required that the output rectifier element Q2 on the forward side be quickly turned off. The delay of turning off the rectifier Q2 appears as an increase in the control delay time tx by the mag amplifier circuit shown in FIG. 2, and as a result, the forward output rectifier Q2 and the flywheel output rectifier as in the conventional device. Element Q3
It does not lead to the generation of a short-circuit current between them.

The output rectifier Q on the flywheel side
In FIG. 3, when the voltage VL1 of the supersaturated reactor L1 becomes high, the gate thereof becomes high via the resistor R1, the diode D4 and the resistor R6, and the output rectifier Q3 is turned on.

Next, the voltage VL1 of the supersaturated reactor L1 becomes 0
Even near V, the output rectifier Q3 on the flywheel side
Parasitic capacitance between the gate and source (shown by a dotted line in FIG. 1) C
1, the output rectifying element Q3 maintains the ON state, and when the voltage VL1 becomes negative (t1), the output of the comparator IC2 of the output rectifying element control circuit 4 becomes negative. Output rectifier Q3 on flywheel side
Turns off. This is because the forward side output rectifier Q
2 is before the time (t2) when it is turned on.

The output rectifier Q3 on the flywheel side
During the period from when is turned off to when the forward-side output rectifying element Q2 is turned on, the rectified current of the second output circuit is equal to the parasitic capacitance C1 of the output rectifying element Q3 or the lowermost column in FIG. As shown by the dotted line, the current flows through the diode D7 connected in parallel with the output rectifier Q3.

Therefore, the forward-side output rectifier Q2
At the time (t2) when the switch is turned on, the same short-circuit current as in the conventional example can be prevented from flowing between these output rectifiers Q2 and Q3, and loss due to the short-circuit current can be avoided to improve efficiency. .

(Embodiment 2) FIG. 3 shows a composite output switching power supply unit according to Embodiment 2 of the present invention. In the forward system, a first side is provided on the secondary side of a transformer T0.
A first output circuit for outputting the output V1 of the
And a second output circuit for outputting 2. In the composite output switching power supply of the second embodiment, the same elements as those of the composite output switching power supply of the first embodiment shown in FIG.

The composite output switching power supply according to the second embodiment has substantially the same configuration as the composite output switching power supply according to the first embodiment shown in FIG. 1, except that the output rectifier control circuit 4 is omitted. First output circuit, second output circuit
The output rectifying element control circuit 10 provided between the two output circuits outputs an OFF signal which turns off the flywheel side output rectifying element Q3 in the second output circuit before the forward side output rectifying element Q2 is turned on. The output circuit is characterized in that it is supplied to the output rectifier Q3 on the flywheel side in the output circuit No. 2.

The output rectifier control circuit 10 has an input terminal connected to a connection point between a diode D5 as a forward output rectifier of the first output circuit and a diode D6 as a flywheel output rectifier. And the second
Output rectifier Q on the flywheel side in the output circuit of FIG.
It is composed of an inverter 11 whose output terminal is connected to the gate 3.

According to the composite output switching power supply of the second embodiment, the rectified voltage of the pulse voltage VT1 induced in the first winding nS1 of the transformer T0 is supplied to the inverter 1
1 and is used as a drive signal for the gate of the output rectifier Q3 on the flywheel side in the second output circuit. As a result, a drive signal having the same waveform as the drive signal of the gate of the output rectifier Q3 in the first embodiment shown in FIG. 2 is obtained, and the flywheel output rectifier in the second output circuit is obtained. Q3 is turned off before the output rectifier element Q2 on the forward side is turned on, thereby preventing the occurrence of short-circuit current and improving the efficiency of the composite output switching power supply of the second embodiment.

In addition to the above-mentioned case, the present invention can of course be similarly applied to a composite output switching power supply for supplying a large number of outputs, such as three outputs and four outputs, to respective loads.

[0046]

According to the first aspect of the present invention, it is possible to reliably prevent a short-circuit current from flowing between the rectifying element on the forward side and the rectifying element on the flywheel side, thereby improving the output efficiency. A power supply can be provided.

According to the second aspect of the present invention, a short-circuit current flows between the rectifying element on the forward side and the rectifying element on the flywheel side in the second output circuit using the rectified output in the first output circuit. , And a composite output switching power supply device capable of improving efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a composite output switching power supply device according to Embodiment 1 of the present invention.

FIG. 2 is a timing chart showing waveforms of respective units in the composite output switching power supply according to Embodiment 1 of the present invention.

FIG. 3 is a circuit diagram showing a composite output switching power supply device according to Embodiment 2 of the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional switching power supply device.

FIG. 5 is a timing chart showing waveforms at various parts in a conventional switching power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply 2 PWM control part 3 Output voltage feedback circuit 4 Output rectification element control circuit 5 Output control circuit 10 Output rectification element control circuit 11 Inverter C1 Parasitic capacitance C2 Smoothing capacitor C3 Smoothing capacitor IC1 Comparator IC2 Comparator L1 Supersaturation reactor L2 Inductor L3 Inductor Q Forward-side MOSFET Q Flywheel-side MOSFET NP Primary winding PD Light emitting diode PH1 Photocoupler PT0 Phototransistor Q1 Main switch Q2 Output rectifier Q3 Output rectifier Q4 Transistor R01 Load R02 Load T0 Transformer V1 Output V2 Output Vin DC Voltage Vref Reference voltage nS1 Secondary winding nS2 Secondary winding

Claims (2)

[Claims] An input voltage is switched by a switching operation for controlling an ON / OFF time of a main switch and supplied to a primary side of a transformer.
A mag-amp circuit, and a forward-type composite output switching power supply device having at least an output circuit that obtains a rectified output using a forward-side and a flywheel-side output rectifying element. It has an output rectifying element control circuit that supplies an off signal for detecting and turning off the flywheel side output rectifying element before the forward side output rectifying element is turned on to the flywheel side output rectifying element. Output switching power supply. 2. An input voltage is switched by a switching operation for controlling an ON / OFF time of a main switch and supplied to a primary side of a transformer.
A first output circuit that obtains a rectified output using forward and flywheel output rectifiers, a mag amplifier circuit, and a rectifier circuit that obtains a rectified output using forward and flywheel output rectifiers. A second output circuit comprising: a forward-type composite output switching power supply device comprising: a first output circuit connected to a connection point of an output rectifier on a forward side and a flywheel side of the first output circuit; The on-state of the main switch is detected from the output of the wheel-side output rectifier, and an off signal for turning off the flywheel-side output rectifier in the second output circuit before the forward-side output rectifier on is detected. An output rectifier control circuit that supplies the output rectifier on the flywheel side in the second output circuit. Composite output switching power supply device according to claim and.