JPH07101989B2 - Switching power supply - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a switching power supply, which uses a voltage generated in a winding provided separately from a main winding in a power conversion transformer, so as to be self-excited. A switching power supply is provided.

<Prior art> Switching power supplies are flyback. Under the converter type, forward.
It can be roughly divided into converter type. It can be divided into a self-excited type and a separately excited type, depending on the configuration method of the oscillator for causing the main switching element to perform a switching operation.The self-excited type has a smaller number of parts and a smaller size than the separately excited type. , Low price. Of these, the self-excited flyback. The converter type has ringing. Chalk. It is a popular converter, and it has a low price,
Widely used as a small output switching power supply.

On the other hand, forward. In the converter type switching power supply, as a conventional example having a self-excited circuit configuration, Royer Push. pull. There is an inverter type.

<Problems to be Solved by the Invention> Among the various switching power supplies described above, as a switching power supply that adopts the separately excited method, a one-stone forward converter, a DC superposition type flyback converter, and the like are known. Since the main switching element is driven by a separately provided oscillator, many circuit components are required, and it is difficult to realize a small-sized and low-cost one. Of the self-excited ones, ringing. Chalk. The converter type switching power supply is
The switching element has low utilization efficiency and can be used only for small electric power. pull. The inverter type switching power supply has a problem that the voltage control on the primary side is impossible because the duty on one side is fixed at 50%.

It is an object of the present invention to provide a self-exciting converter that has a simple circuit configuration, is small in size, and is inexpensive, and provides a stable output with respect to input fluctuations, and is suitable for suppressing output fluctuations due to load electric drive. To provide power.

<Means for Solving the Problems> In order to solve the problems described above, the present invention provides a transformer, a switching element for turning on and off a DC input voltage applied through a first winding of the transformer, and A switching power supply comprising a smoothing circuit for rectifying and smoothing a switching output extracted to a second winding of a transformer, the third power supply biasing a control electrode of the switching element in a positive direction during an ON period of the switching element. A first circuit for shorting the winding and the input side of the switching element to turn off the switching element
And a second driving circuit for turning on the switching element
And a positive feedback action is applied to the control electrode side of the switching element through the first winding and the third winding of the transformer, whereby the switching element is turned on, A step in which the control electrode side of the switching element is short-circuited and driven off by the first drive circuit; and a predetermined off time is taken after the switching element is turned off by the first drive circuit, By repeating the step of ON-driving the switching element by the second drive circuit, the switching element continues the ON / OFF operation by self-excitation, and the DC input voltage is turned ON / OFF. And

<Operation> In the switching power supply according to the present invention having the above configuration, when a DC input voltage is applied and the switching element is activated, a positive voltage is applied to the input side of the switching element through the first winding and the third winding of the transformer. The feedback action is added, and the switching element is turned on rapidly. In this way, when the switching element is turned on, the input side of the switching element is short-circuited and is turned off by the first drive circuit.

On the other hand, in the second drive circuit, after the switching element is turned off by the first drive circuit, the switching element is turned on for a predetermined off time.

By repeating the above operation, the switching element 2 continues to turn on and off by self-excitation, and the DC input voltage is turned on and off.

In this case, the second drive circuit turns on the input voltage and turns on. It is possible to perform an oscillating operation such that the product of the duty is constant. For example, when the input voltage doubles, it turns on. By controlling the duty to be 1/2, a stable output can be obtained against input fluctuations.

<Example> FIG. 1 is an electric circuit diagram of a switching power supply according to the present invention. In the figure, 1 is a power conversion transformer, 101 is a first winding provided in the transformer 1, 102 is a second winding, and 103 is a third winding.

2 is a main switching element. In this embodiment, it is composed of a field effect transistor, the drain D is connected to the DC power source (+ Vin) via the first winding 101, and the source S is connected to the DC power source via the winding 41 of the current transformer 4. It is connected to (-Vin).

Reference numeral 5 is an output circuit connected to the second winding 102. The output circuit 5 connects one end of a saturable reactor 51, which constitutes a magnetic amplifier, to one end of the second winding 102, and at the subsequent stage of the saturable reactor 51, a rectifier circuit 52 and a choke. Connect the input type smoothing circuit 53 and output DC from the smoothing circuit 53
To get. A control circuit 54 detects the DC output voltage Vo and controls the saturable reactor 51 based on the detection signal so that the DC output voltage Vo becomes constant. The output stabilizing action of the saturable reactor 51 and the control circuit 54 will be described later.

The rectifier circuit 52 includes a forward rectifier diode 52.
a and a commutation diode 52b in the flywheel direction,
The smoothing circuit 53 is composed of a choke coil 53a and a capacitor 53b.

Reference numeral 6 is a first drive circuit that short-circuits the input side of the switching element 2 to turn it off. In this embodiment, the first drive circuit 6 turns off the switching element 2 so that the first drive circuit 6 has an on-time width that is substantially inversely proportional to the voltage value generated in the third winding 103 provided in the transformer 1. ing. Third winding 10
A time constant charging circuit 61 including a resistor 61a and a capacitor 61b is connected to both ends of the capacitor 3, and both ends of the capacitor 61b forming the time constant charging circuit 61 are connected to the base of the transistor 62. It is connected between the emitters, and the collector and the emitter of the transistor 62 are connected between the input ends of the switching element 2 via the diode 63. Therefore, the capacitor
When the charging voltage Vcl of 61b reaches a predetermined value and the transistor 62 is turned on, the input side of the switching element 2 is short-circuited by the transistor 62 and the switching element 2 is turned off. 64 is a capacitor, 65 is a resistor, and 66 is a diode.

Reference numeral 7 is a second drive circuit for turning on the switching element 2. In this embodiment, the second drive circuit 7 rectifies and smoothes the voltage generated in the third winding 103 and turns it on with the input voltage.
A voltage proportional to the duty is created, this voltage is compared with a reference voltage, and the switching element is turned on by the comparison output. A first rectifier circuit 71 and a second rectifier circuit 72 that rectify the voltage generated in the third winding 103 when the switching element 2 is turned on are connected to one end of the third winding 103. A circuit 73 for smoothing the rectified output is provided at the subsequent stage of the first rectifier circuit 71. The circuit 73 is composed of a resistor 73a, a capacitor 73b and a resistor 73c.
Further, in the subsequent stage of the second rectifier circuit 72, capacitors 74 and 75 for smoothing the rectified output, and a reference voltage source circuit 76 composed of a Zener diode for producing a reference voltage from the smoothed DC voltage.
Are connected. 77 and 78 are resistors for voltage drop.

Then, the DC output voltage Vc2 of the circuit 73 and the reference voltage source circuit 7
The reference voltage Vz1 of 6 is input to the comparison circuit 79, and the switching element 2 is turned on by the comparison output. In this embodiment, the comparison circuit 79 is composed of a transistor, the base of which is provided with the DC output voltage Vc2 of the circuit 73, and the emitter of which is provided with the reference voltage Vz1 from the reference voltage source circuit 76.
To perform a comparison operation, and the comparison output is input to the gate G of the switching element 2 through the diode 8.

Note that a fourth winding different from the third winding 103 may be provided and the second drive circuit 7 may be connected to this fourth winding.

Reference numeral 9 is an overcurrent protection circuit. The overcurrent protection circuit 9 has a second
The emitter of the transistor 91 is connected to both ends of the reference voltage source circuit 76 which constitutes the drive circuit 7 of FIG. The collector of the transistor 92 is connected to the base of the transistor 91, and the collector of the transistor 92 is connected via the diode 93 to the base of the transistor 92. The emitter is connected to both ends of the winding 42 of the current transformer 4 via the Zener diode 94 and the diode 95. Also, the collector of the transistor 92. The emitter is connected to the gate input terminal of the switching element 2 via the diode 96. 10 is a switching element 2
Is a starting resistance for activating, and 97 to 99 are resistances.

Next, the operation of the above embodiment will be described. When a DC input voltage (+ Vin, −Vin) is applied, the potential of the gate G of the switching element 2 rises through the starting resistor 10, the switching element 2 is turned on, and the first winding 10 of the transformer 1 is turned on.
A current flows through the first winding 101, a voltage is induced in the first winding 101, and a voltage depending on the turn ratio with the first winding 101 is generated in the third winding 103. The voltage induced in the third winding 103 is applied to the gate G of the switching element 2 through the capacitor 64 and the resistor 65, and the positive feedback action of increasing the gate potential is applied, so that the switching element 2 is rapidly turned on.

When the switching element 2 is turned on as described above, the first turn-on voltage generated in the third winding 103 causes the first turn-on voltage.
In the drive circuit 6 of, the capacitor 61b of the time constant charging circuit 61
Is charged through the resistor 61a, and its charging terminal voltage Vc1 rises with time. The charging terminal voltage Vc1 is the base of the transistor 62. When the emitter-to-emitter ON voltage Vbe rises, the transistor 62 turns ON, and the gate. The sources are short-circuited by the transistor 62, and the switching element 2 is turned off. Here, the charging terminal voltage Vc1 of the capacitor 61b is the DC input voltage (+ Vin,
As −Vin) becomes higher, the time to reach the on-voltage Vbe becomes faster, the timing at which the switching element 2 is turned off becomes earlier, and the on-time width becomes shorter. Conversely,
If the DC input voltage (+ Vin, -Vin) becomes low, the timing at which the switching element 2 is turned off is delayed, and the on time width becomes long. In other words, the first drive circuit 6 uses the DC input voltage (+ Vin, −Vi) applied via the third winding 103.
The switching element 2 is driven off so as to have an on-time width that is substantially inversely proportional to n).

On the other hand, when the switching element 2 is turned on, in the second drive circuit 7, the voltage induced in the third winding 103 is rectified by the second rectifier circuit 72, stepped down by the resistors 77, 78, and further capacitored. It is converted into direct current by 75, and a constant reference voltage Vz1 as shown in FIG. 2 is obtained by the reference voltage source circuit 76. Since one end of the reference voltage source circuit 76 is connected to the emitter of the transistor 79, the emitter of the transistor 79 is kept at the substantially constant reference voltage Vz1.

At the same time, the voltage induced in the third winding 103 is rectified through the first rectifier circuit 71, the rectified output is converted into a DC voltage by the circuit 73, and rises at a constant slope as shown in FIG. A DC voltage signal is obtained. In this case, the terminal voltage Vc2 of the capacitor 73b, which becomes a DC voltage signal, turns on with the input voltage. The value is almost proportional to the duty.

Next, when the switching element 2 is turned off by the operation of the first drive circuit 6, the capacitor 73b forming the circuit 73 is formed.
The electric charge accumulated in the capacitor is discharged through the resistor 73c, and the terminal voltage Vc2 decreases as shown in FIG. Then, when the terminal voltage Vc2 tries to become a value lower than the reference voltage Vz1,
Since the transistor forming the comparison circuit 79 is turned on and a voltage is applied to the gate G of the switching element 2 through the diode 8, the switching element 2 is turned on.

By repeating the above operation, the switching element 2 continues the ON / OFF operation, and the DC input voltage (+ Vin, −Vi
n) is turned on and off. In this case, the first drive circuit 6
Causes the switching element 2 to be turned off so that the voltage-time product becomes constant, and the second drive circuit 7 causes
Input voltage and on. The switching element 2 is ON-controlled so that the product of the duty is constant. For example, when the input voltage doubles, it turns on. 1/2 duty
Since it is controlled so that a stable output can be obtained against an input fluctuation.

Here, the output stabilizing action of the magnetic amplifier including the saturable reactor 51 will be described. First, it is assumed that the saturable reactor 51 is saturated during the ON period of the switching element 2 and the load current flows to reach the point a on the BH curve in FIG.

Next, during the off period of the switching element 2, the diode 52
a is blocked. In this state, the control circuit 54 resets the saturable reactor 51 in the direction opposite to the reset current
When Ir is flown, saturable reactor 51 is reset to point c through point b in FIG. When the switching element 2 is turned on again, the saturable reactor 51 is saturated along the path of point c → d point → a in FIG. At this time, the saturable reactor 51 has a voltage drop ΔV corresponding to the magnetic flux change amount of (ΔB1 + ΔB2) in FIG. Therefore, if the reset current Ir flowing from the control circuit 54 to the saturable reactor 51 is adjusted according to the output voltage Vo and the point c, which is the reset point, is controlled, the voltage drop ΔV of the saturable reactor 51 is output voltage.
The output voltage can be stabilized by variably adjusting according to Vo.

Here, in the present invention, the first drive circuit 6 and the second drive circuit 6
Since the driving circuit 7 has a stabilizing effect against the input fluctuation, the saturable reactor 51 has a load current Io.
It is only necessary to compensate for the increase in the frequency band, that is, the fluctuation of the voltage drop in the diode 52a, the choke coil 53a, etc. due to the load driving. Therefore, the load on the saturable reactor 51 is significantly reduced.

Next, the operation of the overcurrent protection circuit 9 will be described. When the current I1 flowing through the switching element 2 becomes excessive and the Zener diode 94 becomes conductive due to the voltage generated on the winding 42 side of the current transformer 4, the transistor 92 is turned on. When the transistor 92 is turned on, the gate circuit of the switching element 2 is short-circuited via the diode 96, and at the same time,
The transistor 91 is turned on and the reference voltage Vz1 drops,
Output decreases. As a result, an overcurrent protection effect is obtained.

FIG. 4 is an electric circuit diagram of another embodiment of the switching power supply according to the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same components. In this embodiment, an output stabilizing action against a load change is provided without using a supersaturated reactor, and the light receiving element 11a is arranged in parallel with the reference voltage source circuit 76 constituting the second drive circuit 7.
A light emitting element 11b forming a photo coupler together with the light receiving element 11a is connected to the control circuit 54, the output control signal of the control circuit 54 is transmitted from the light emitting element 11b to the light receiving element 11a, and the reference voltage Vz1 is output. Control according to the voltage Vo.
As a result, the reference voltage Vz1 input to the comparison circuit 79 is controlled, so that the output stabilizing action is performed.

The comparison operation by the comparison circuit 79 is performed by using the reference voltage Vz1 and the circuit 73
Of the DC output voltage Vc2 of the circuit 73.
The DC voltage signal Vc2 may be adjusted. For example, the light receiving element 11a may be connected in series or in parallel with the resistor 73a.

<Effects of the Invention> As described above, according to the present invention, a self-exciting converter having a simple circuit configuration, a small size, and a low cost, capable of obtaining a stable output with respect to an input fluctuation, and a magnetic amplifier It is possible to provide a switching power supply suitable for combination to reduce the load thereof and also suppress the output fluctuation due to the load fluctuation. In the description of the present invention, the one-stone forward converter has been described as an example. However, if the polarity of the conversion transformer is changed, it can be applied to the DC superposition type flyback converter, and in this case, rectification is possible. Since the smoothing circuit may be of the capacitor input type, further miniaturization is possible.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a switching power supply according to the present invention,
FIG. 2 is a waveform diagram for explaining the circuit operation, FIG. 3 is a BH and hysteresis characteristic diagram for explaining the operation of the magnetic amplifier, and FIG. 4 is for another embodiment of the switching power supply according to the present invention. It is an electric circuit diagram. 1 ... Transformer, 101 ... First winding 102 ... Second winding, 103 ... Third winding 2 ... Switching element 5 ... Output circuit 6 ... First drive circuit 7 ... Second drive circuit

Claims (10)

[Claims] 1. A transformer, a switching element for turning on and off a direct-current input voltage applied through a first winding of the transformer, and a switching output extracted to a second winding of the transformer. A switching power supply comprising: a smoothing circuit for rectifying and smoothing, wherein a third winding for biasing a control electrode of the switching element in a positive direction during an ON period of the switching element and an input side of the switching element are short-circuited to perform switching. A first drive circuit for turning off the element, and a second drive circuit for turning on the switching element, and a control electrode of the switching element through the first winding and the third winding of the transformer After a positive feedback action is applied to the side of the switching element and the switching element is turned on by the positive feedback action, the control electrode side of the switching element is short-circuited by the first drive circuit. And being turned off, and a step of turning on the switching element by the second driving circuit after a predetermined off time after the switching element is turned off by the first driving circuit. The switching power supply is characterized in that the switching element continues to turn on and off in a self-excited manner by repeating the above, and the DC input voltage is turned on and off. 2. The first drive circuit according to claim 1, wherein the first drive circuit is a circuit for turning off the swinging element so that the first drive circuit has an on-time width substantially inversely proportional to the input voltage. Switching power supply. 3. The first driving circuit is turned on when a time constant charging circuit charged by a voltage generated in the third winding and a charging voltage of the time constant charging circuit reaches a predetermined value. The switching power supply according to claim 1 or 2, further comprising: a transistor that short-circuits an input side of the switching element. 4. The time constant charging circuit, wherein the first driving circuit is charged by a voltage generated in a winding different from the third winding, and the charging voltage of the time constant charging circuit becomes a predetermined value. The switching power supply according to claim 1 or 2, further comprising a transistor that is turned on when the switching element is turned on to short-circuit the input side of the switching element. 5. The second drive circuit rectifies and smoothes the voltage generated in the third winding, and turns on the input voltage and the ON voltage. 2. A circuit for producing a direct current voltage signal substantially proportional to a duty, comparing the direct current voltage signal with a reference voltage, and turning on the switching element by the comparison output thereof. The switching power supply according to item 2 or 3. 6. The second drive circuit rectifies and smoothes a voltage generated in a winding different from the third winding to turn on the input voltage. 2. A circuit for producing a direct current voltage signal substantially proportional to a duty, comparing the direct current voltage signal with a reference voltage, and turning on the switching element by the comparison output thereof. The switching power supply according to item 2 or 3. 7. The second drive circuit rectifies and smoothes a voltage generated in the third winding or a winding different from the third winding when the switching element is turned on, and turns on. A circuit for obtaining a DC voltage signal substantially proportional to the duty and the input voltage, and a DC voltage signal obtained by rectifying and smoothing the voltage generated in the third winding or a winding different from this when the switching element is turned on. A reference voltage source circuit that makes a more reference voltage,
7. The circuit according to claim 6, further comprising a circuit for comparing a DC voltage signal output of the circuit and a reference voltage provided from the reference voltage source circuit and turning on the switching element by the comparison output. Switching power supply described in. 8. The second drive circuit comprises an overcurrent protection circuit which operates to turn off the switching element at the same time as lowering the reference voltage by an overcurrent detection signal. The switching power supply according to item 6 or 7. 9. The second drive circuit is optically coupled to a light emitting element driven by a control signal of a control circuit provided in the output circuit, and is controlled by a control signal transmitted from the light emitting element. 9. The switching power supply according to claim 6, further comprising a light receiving element for controlling a reference voltage or a DC voltage signal output of the circuit in a direction in which the output voltage is stable. . 10. The output stabilizing circuit comprising a magnetic amplifier is provided on the output circuit side, and the output stabilizing circuit is provided with a magnetic amplifier, claim 1, claim 2, claim 3, claim 4, claim 5, claim 5. Item 6, Item 7
The switching power supply according to item 8 or 8.