JP2000287460A - Self-exciting switching power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a self-exciting switching power supply circuit which enables stable self-exciting oscillation even if a transistor device with a large input capacity is used. SOLUTION: The base of a 2nd switching transistor Q2 is connected to the drain of a 1st switching transistor Q1 via a series circuit consisting of a resistor R3 and a capacitor C2. On the other hand, the gate of the 1st switching transistor Q1 is connected to the collector of the 2nd switching transistor Q2 via an impedance transformation circuit 5a. The impedance transformation circuit 5a consists of a complementary circuit composed of 1st and 2nd transistors Q4 and Q5 whose polarities are different from each other. The connection point between the bases of the transistors Q4 and Q5 is connected to the collector of the 2nd switching transistor Q2. The connection point between the emitters of the transistors Q4 and Q5 is connected to the gate of the 1st switching transistor Q1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for performing a stable self-oscillation operation in a self-excited oscillation type switching power supply circuit even with a large power capacity specification.

[0002]

2. Description of the Related Art There are various types of power supply circuits constituting a power supply device. The power supply circuit is first classified into a series method and a switching method according to the operation mode of the semiconductor element for controlling the output voltage. The switching method is further divided into a self-excited oscillation method and a separately excited oscillation method depending on how a switching pulse is generated. System. A power supply circuit employing a switching system, among which a self-excited oscillation system (hereinafter referred to as a self-excited switching power supply circuit), has a feature that the circuit configuration is relatively simple, and is generally a small-sized and low-power power supply. Applies to equipment. Conventionally, such a self-excited switching power supply circuit has a circuit configuration as shown in FIG.

In the circuit shown in FIG. 3, first, a primary winding N1 of a transformer T and a main current path of a first switching transistor Q6 are connected in series between an input terminal 1 and a ground as a reference potential point. . A connection point between the primary winding N1 and the collector of the first switching transistor Q6 and the DC output terminal 2
, And a capacitor C1 is connected between the DC output terminal 2 and the ground. Then, both ends and an intermediate tap of the secondary winding N2 of the transformer T are connected to the AC output terminals 3a, 3c, 3b, respectively. Thereby, the primary winding N1, the first switching transistor Q6,
The diode D1 and the capacitor C1 form a boost chopper type converter circuit, and the primary winding N1, the secondary winding N2, and the first switching transistor Q6 form an inverter circuit.

[0004] Then, in order to perform a self-excited oscillation operation,
A series circuit of a resistor R1 and a second switching transistor Q2 is provided between the input terminal 1 and the ground, and a resistor R2, a resistor R3 and a capacitor C2 are provided between the collector of the first switching transistor Q6 and the collector of the second switching transistor Q2. Connected in series. The base of the first switching transistor Q6 is connected to a connection point between the resistor R2 and the collector of the second switching transistor Q2. On the other hand, the base of the second switching transistor Q2 is connected to the connection point between the resistors R2 and R3, and the base is connected to the collector of the first switching transistor Q6 via the resistor R3 and the capacitor C2. I do.

Further, in order to stabilize the voltage value of the output voltage appearing at each output terminal, a control transistor Q3, voltage dividing resistors R4 and R5, a resistor R6 and a reference voltage source are provided between the DC output terminal 2 and the ground. Constant voltage diode DZ1 as
Is provided, and the collector of the control transistor Q3 is connected to the base of the second switching transistor Q2 via the resistor R7.

In the circuit having the above configuration, the first
When the switching transistor Q6 is turned on and off, voltages having different directions are alternately generated in the primary winding N1 of the transformer T. The combined voltage of the voltage generated at the primary winding N1 and the input voltage is rectified and smoothed by the diode D1 and the capacitor C1, and as a result, a predetermined DC output voltage is obtained at the DC output terminal 2. In addition, voltages having different directions alternately generated in the primary winding N1 are induced in the secondary winding N2, and an AC output voltage is obtained between the output terminals 3a, 3b, and 3c. The on / off operation of the first switching transistor Q6 is continued by a self-excited oscillation operation in which the second switching transistor Q2 and the first switching transistor Q6 are complementarily turned on or off as in a multivibrator circuit. .

[0007]

The self-excited switching power supply circuit having the circuit configuration shown in FIG. 3 has a simple circuit configuration, is highly practical, and mainly has a small output power (about 10 W or less). Widely applied to equipment. However, in the case of a specification having a large output power, there are the following problems, and it has been difficult to use it. As the output capacitance increases, the current passing through the primary winding N1 and the main current path of the first switching transistor Q6 increases, and accordingly, a transistor element having a large current specification must be used for the first switching transistor Q6. . At present, a field effect type power transistor is often used as a transistor element having a large current specification, and such a transistor element is generally used as a control terminal (gate).
The input capacitance equivalent to the above is large.

If such an element having a large input capacitance is applied to the first switching transistor Q6 of the circuit shown in FIG. 3 as it is, the self-sustained pulsation of the circuit becomes unstable and the circuit does not operate normally. there were. Incidentally, it has been confirmed by experiments that if a power transistor formed of a MOSFET is used as the first switching transistor Q6 as it is, the second switching transistor Q2 may be in a semi-conductive state depending on conditions, and the whole circuit may not perform a self-excited oscillation operation. . Therefore, an object of the present invention is to provide a self-excited switching power supply circuit that enables stable self-excited oscillation operation even when a transistor element having a large input capacitance is used, and is thus applicable to a specification with a large output capacitance. .

[0009]

SUMMARY OF THE INVENTION A self-excited switching power supply circuit according to the present invention comprises a first circuit which alternately turns on and off.
One end of a main current path of the second switching transistor in a self-excited switching power supply circuit having a second switching transistor and a second switching transistor, and intermitting a current flowing into the inductance component by the first switching transistor to obtain a desired output voltage. An impedance conversion circuit is connected between the first switching transistor and a control terminal of the first switching transistor.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A primary circuit of a transformer and a series circuit of a first switching transistor and a series circuit of a resistor and a second switching transistor are connected in parallel between an input terminal and a ground. A control terminal of the second switching transistor is connected to a connection point between the main current path of the first switching transistor and the primary winding via a series circuit of a resistor and a capacitor. On the other hand, the control terminal of the first switching transistor is connected to a connection point between the second switching transistor and the resistor via the impedance conversion circuit.
Here, the impedance conversion circuit is constituted by a complementary connection circuit of first and second transistors having different polarities connected between the input terminal and the ground, and a connection point between the bases is connected to a main current of the second switching transistor. And a connection point between the emitters and a control terminal of the first switching transistor.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit diagram of a self-excited switching power supply circuit according to an embodiment of the present invention, which can perform a stable self-excited oscillation operation even when a transistor element having a large input capacitance is used. The circuit shown in FIG.
The primary current path of the primary winding N1 of the transformer T and the first switching transistor Q1 composed of an N-channel MOSFET are connected in series between the ground and the ground. A diode D1 is connected between the DC output terminal 2 and a connection point between the primary winding N1 and the drain of the first switching transistor Q1,
The capacitor C1 is connected between the DC output terminal 2 and the ground. Then, both ends and an intermediate tap of the secondary winding N2 of the transformer T are connected to the AC output terminals 3a, 3c, 3b, respectively.

A series circuit of a resistor R1 and a second switching transistor Q2 is connected between the input terminal 1 and the ground,
A resistor R is connected between the drain of the first switching transistor Q1 and the collector of the second switching transistor Q2.
2. Connect a series circuit of a resistor R3 and a capacitor C2. The gate of the first switching transistor Q1 is connected to the collector of the second switching transistor Q2 via the impedance conversion circuit 5. The base of the second switching transistor Q2 is connected to a connection point between the resistors R2 and R3.

A control circuit 4 comprising a control transistor Q3, voltage dividing resistors R4, R5, a resistor R6 and a constant voltage diode DZ1 as a reference voltage source is provided between the DC output terminal 2 and the ground. The circuit configuration is such that the collector is connected to the base of the second switching transistor Q2 via the resistor R7. With such a circuit configuration, the input capacitance C _in the presence equivalently by the impedance conversion circuit 5 in the first switching transistor Q1 and the second switching transistor Q2
Is separated from the collector and emitter. as a result,
Is eliminated operational adverse effects caused by the input capacitance C _in, self-oscillation operation of the circuit is to be carried out stably.

FIG. 2 is a circuit diagram of a self-excited switching power supply circuit according to the present invention, showing the circuit portion of the impedance conversion circuit 5 of the circuit of FIG. 1 more specifically. In FIG. 2, the impedance conversion circuit 5a connects a series circuit of a transistor Q4 and a transistor Q5 having their emitters and bases connected between the input terminal 1 and the ground. The connection point between the bases is connected to the collector of the second switching transistor Q2, and the connection point between the emitters is connected to the gate of the first switching transistor Q1. The operation of the self-excited switching power supply circuit according to the present invention to which such an impedance conversion circuit is added is as follows.

When an input voltage is applied to the input terminal 1, the impedance conversion circuit 5 is connected to the input terminal 1 via the resistor R1.
A current flows into a, and the transistor Q4 is turned on and the transistor Q5 is turned off inside the impedance conversion circuit 5a. Then, the input voltage is applied to the gate of the first switching transistor Q1 via the transistor Q4, and the first switching transistor Q1 is turned on. At this time, the second switching transistor Q2 cannot receive a forward bias required to turn on between its base and emitter, and
It turns off. When the first switching transistor Q1 is turned on, a current that linearly increases starts flowing through the primary winding N1 of the transformer T.

When the value of the current flowing through the primary winding N1 reaches the drain saturation current of the first switching transistor Q1, which is determined by the voltage between the gate and the source, the current flowing through the primary winding N1 becomes constant. , There is no potential difference between the terminals of the primary winding N1. At this time, a current flows from the primary winding N1 to the base of the second switching transistor Q2 via the capacitor C2 and the resistor R3.
The switching transistor Q2 is turned on. Then, the transistor Q4 in the impedance conversion circuit 5a is turned off, and the transistor Q5 is turned on, so that the first switching transistor Q1 is turned off. With the transition of the first switching transistor to the off state, a flyback voltage is generated in the primary winding N1.

While the first switching transistor Q1 is in the off state and the second switching transistor Q2 is in the on state, current flows from the primary winding N1 to the capacitor C2, and the capacitor C2 places a high potential on the primary winding N1 side. Will be charged. When the charging of the capacitor C2 proceeds, the second
The base current of the switching transistor Q2 decreases,
Eventually, the second switching transistor Q2 shifts to the off state. When the second switching transistor Q2 is turned off, the transistor Q4 is turned on inside the impedance conversion circuit 5a, and the transistor Q5 is turned on.
Is turned off, and accordingly, the first switching transistor Q1 is turned on again. By repeating the above operation, the circuit shown in FIG. 2 performs a self-excited oscillation operation.

In the above description of the embodiment of the present invention, an N-channel type MOSF
Although it is assumed that ET is used, the present invention is not limited to this, and another type of transistor may be used. In the self-excited switching power supply circuit according to the present invention, a bipolar transistor for high power can be applied to the first switching transistor Q1, and in this case, a resistance element is added to the collector or the emitter of the transistor Q4 of the impedance conversion circuit. Sometimes. It goes without saying that the impedance conversion circuit can be modified within a range that does not impair the gist of the present invention.

[0019]

As described above, the self-excited switching power supply circuit according to the present invention is configured such that the first and second switching transistors operate in a complementary manner like a flip-flop circuit, and has a large input capacitance for large power. In the power supply circuit in which the transistor element is applied to the first switching transistor, an impedance conversion circuit is connected between a control terminal of the first switching transistor and one end of a main current path of the second switching transistor. With such a configuration, the input capacitance of the first switching transistor and the second switching transistor can be separated by the impedance conversion circuit, and a stable self-pulsation operation can be performed even when a transistor element having a large input capacitance is used. It becomes possible. As a result, it is possible to provide a self-excited switching power supply circuit that can be applied to a specification having a large output capacity.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a self-excited switching power supply circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a self-excited switching power supply circuit according to an embodiment of the present invention, specifically showing the configuration of the impedance conversion circuit.

FIG. 3 is a circuit diagram of an example of a conventional self-excited switching power supply circuit.

[Explanation of symbols]

1: Input terminal 2: DC output terminal 3a-3
c: AC output terminal 4: Control circuit 5, 5a:
Impedance conversion circuit N1: primary winding N2: secondary winding Q1: first switching transistor Q2: second switching transistor
Q4: Transistor (first transistor) Q5: Transistor (second transistor) T: Transformer (inductance part)

Claims (3)

[Claims] 1. A first and a second means for alternately performing on and off operations.
A self-excited switching power supply circuit that obtains a desired output voltage by intermittently flowing a current flowing into an inductance component by the first switching transistor; and one end of a main current path of the second switching transistor. A self-excited switching power supply circuit, wherein an impedance conversion circuit is connected between the switching terminal and a control terminal of the first switching transistor. 2. The impedance conversion circuit, wherein a connection point between bases is connected to one end of a main current path of the second switching transistor, and a connection point between emitters is connected to a control terminal of the first switching transistor. The self-excited switching power supply circuit according to claim 1, further comprising a complementary connection circuit of a first transistor and a second transistor having different polarities. 3. The self-excited switching power supply circuit according to claim 1, wherein the first switching transistor is a field effect transistor.