JPH1014236A - Self excitation-type of switching power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self excitation-type of switching power unit which is high in conversion efficiency by supporting the occurrence of superfluous loss, occurring in a circuit. SOLUTION: A transistor Q3, as an auxiliary switch of reverse junction type to the second switching transistor Q2, is connected to the resistor R1 as an impedance element for bias supply, connected between the junction between the collector of the second switching transistor Q2 and the base of the first switching transistor Q1 and an input terminal 1. The base of the transistor Q3 is connected to the ground (input terminal on low potential side) through a resistor R5, and further the base is connected to the junction between the first switching transistor Q1 and the primary winding N1 of a transistor T, through a capacitor C5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving the conversion efficiency of a self-excited oscillation type switching power supply.

[0002]

2. Description of the Related Art The driving system of a switching power supply is roughly classified into a self-excited oscillation system and a separately excited oscillation system. The former self-excited oscillation system is applied to a power supply device having a relatively small capacity. As a switching power supply device of this self-excited oscillation type (hereinafter referred to as self-excited type), there is one having a circuit configured as shown in FIG. In FIG. 3, reference numerals 1 and 2 denote input terminals and output terminals on the high potential side, and both the input terminals and the output terminals on the low potential side are considered to be the same as the ground because both are connected to the ground. is there. Here, the ground is not necessarily grounded, but indicates a reference potential point of the circuit.

A transformer T is connected between the input terminal 1 and the ground.
The primary winding N1 and the first switching transistor Q1 are connected in series, and the secondary winding N2 of the transformer T has one end connected to the output terminal 2 via the rectifier diode D1, and the other end connected to the ground. ing. A filter capacitor C1 is connected between the input terminal 1 and the ground, and a smoothing capacitor C2 is connected between the output terminal 2 and the ground. The first switching transistor Q1, the transformer T, the rectifying diode D1, By the smoothing capacitor C3,
It constitutes a circuit of a general power supply device. The following components are further connected to this circuit for self-excited oscillation.

A resistor R1 and a second switching transistor Q2 are connected in series between the input terminal 1 and the ground.
The collector of the second switching transistor Q2 is connected to the base of the first switching transistor Q1, and the base is connected to the collector of the first switching transistor Q1 via a series circuit of a resistor R2 and a capacitor C3. A resistor R3 and a resistor R4 are connected in series between the base of the second switching transistor Q2 and the base of the first switching transistor Q1, and the resistors R3 and R
The connection point 4 is connected to the ground and the output terminal 2 via a series circuit of a capacitor C4, a diode D2 and a constant voltage diode DZ1. The outline of the self-excited oscillation operation of the circuit having the above configuration is as follows.

When an input voltage is applied to the input terminal 1, a current flows from the input terminal 1 to the base of the first switching transistor Q1 via the resistor R1, and the first switching transistor Q1 receives a forward bias and turns on. State. At this time, the portion between the base and the emitter of the second switching transistor Q2 cannot be subjected to a forward bias necessary for turning on, and is turned off. When the first switching transistor Q1 is turned on, a linearly increasing current starts flowing through the primary winding N1 of the transformer T, and at the same time, the capacitor C3 is charged with the resistor R2 being at a high potential. .

Here, the first switching transistor Q
The upper limit of the collector current of 1 (hereinafter referred to as the collector saturation current) varies depending on the value of the current flowing through the base at that time, and is set substantially constant by the resistor R1 in the circuit having the configuration of FIG. When the value of the current flowing through the primary winding N1 reaches the collector saturation current of the first switching transistor Q1, the current flowing through the primary winding N1 becomes constant, and at that moment, the potential difference between the terminals of the primary winding N1. Disappears. At this time, the capacitor C3 starts discharging, supplies a base current to the second switching transistor Q2, and makes the second switching transistor Q2 conductive. Then, the base current of the first switching transistor Q1 decreases, and the flow rate of the collector current of the first switching transistor Q1 is reduced, so that a flyback voltage is generated in each winding of the transformer T.

The flyback voltage generated in the primary winding N1 is applied to the base of the second switching transistor Q2 via the capacitor C3 and the resistor R2, and guides the second switching transistor Q2 to an ON state. When the second switching transistor Q2 is turned on, the first
The base potential of the switching transistor Q1 decreases,
The forward bias state is released, and the first switching transistor Q1 is turned off. While the second switching transistor Q2 is in the ON state, a current flows through the base of the second switching transistor Q2 via the primary winding N1, the capacitor C3, and the resistor R2, and the capacitor C3
Has a primary winding N1 and a first switching transistor Q1.
The charging is performed by setting the connection point (hereinafter referred to as connection point (a)) to a high potential.

As the charging of the capacitor C3 progresses, the base current of the second switching transistor Q2 decreases, and the second switching transistor Q2 shifts to the off state soon. When the second switching transistor Q2 is turned off, a current flows again into the base of the first switching transistor Q1 via the resistor R1, and the first switching transistor Q1 shifts to the on state. The self-excited oscillation operation is performed by repeating the above operation. The series circuit of the diode D2 and the constant voltage diode DZ1 outputs a signal corresponding to the output voltage to the resistor R3.
To the base of the second switching transistor Q2 to change the on-duty of the second switching transistor Q2. As a result, the on-duty of the first switching transistor Q1 changes and acts to keep the output voltage constant.

[0009]

In the circuit shown in FIG. 3, when the first switching transistor Q1 is in the ON state and the second switching transistor Q2 is in the OFF state, the current passing through the resistor R1 is equal to the current flowing through the resistor R1. Is turned on. However, when the first switching transistor Q1 is off and the second switching transistor Q2 is on, the current passing through the resistor R1 flows into the collector of the second switching transistor Q2 and does not contribute to anything. Since a loss occurs if a current flows through the resistance element, the circuit shown in FIG. 3 generates an unnecessary loss in the resistor R1 during a period in which the first switching transistor Q1 is off and the second switching transistor Q2 is on. . This has increased the loss generated in the circuit and has been a factor in lowering the conversion efficiency of the power supply device. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a self-excited switching power supply capable of obtaining high conversion efficiency by suppressing generation of useless loss occurring in a circuit.

[0010]

SUMMARY OF THE INVENTION The present invention comprises first and second switching transistors which operate in a complementary manner, wherein current is intermittently connected by the first switching transistor and connected in series to the first switching transistor. In a self-excited oscillation type switching power supply device configured to obtain an output voltage through the obtained inductance component,
The first switching transistor is connected between a control terminal of the first switching transistor, a connection point of a main current path of the second switching transistor, and an input terminal of the power supply device, and is connected to the first switching transistor when the second switching transistor is off. A current path for applying a forward bias is formed, and when the second switching transistor is in an on state, the current path for flowing a current to the second switching transistor is supplied to the impedance element forming the current path. Is characterized in that auxiliary switches which operate complementarily are connected in series.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In addition to a first switching transistor, a second switching transistor is provided, and a series circuit of a resistor and a capacitor is connected between a base of the second switching transistor and a collector of the first switching transistor. By connecting the collector of the second switching transistor and the base of the first switching transistor, the first switching transistor and the second switching transistor perform complementary operations. Between the base of the first switching transistor and the input terminal of the power supply device, a series circuit of an auxiliary switch and a bias impedance element, which operate complementarily to the second switching transistor, is connected. Here, as an example of the auxiliary switch, its base is connected to a connection point between the first switching transistor and the inductance component via a capacitor, and the base is connected to an input terminal via a resistor for setting a base current. Alternatively, it is constituted by a transistor connected to the reference potential point.

[0012]

FIG. 1 shows a circuit diagram of an embodiment of a self-excited switching power supply according to the present invention, which makes it possible to suppress the occurrence of unnecessary loss. 1 having the same functions as the components shown in the circuit of FIG.
The same reference numerals are given. In FIG. 1, a transformer T, a first switching transistor Q1, which is an NPN transistor, and a rectifier diode D1 and a smoothing capacitor C2, which are main components of the power supply circuit, have the same configuration as in FIG. 3, and a description thereof will be omitted. On the other hand, a circuit configuration for performing self-excited oscillation is as follows.

That is, a second switching transistor Q2 is provided which is the same NPN transistor as the first switching transistor Q1, and the collector of the second switching transistor Q2 is the first switching transistor Q2.
1, the emitter is connected to ground, and the base is connected to the collector of the first switching transistor Q1 via a resistor R2 and a capacitor C3. A resistor R3 and a resistor R4 are provided between the base of the second switching transistor Q2 and the base of the first switching transistor Q1.
Are connected in series, and the connection point of the resistor R3 and the resistor R4 is connected to the ground and the output terminal 2 through a series circuit of a capacitor C4, a diode D2 and a constant voltage diode DZ1, respectively. The connection point between the collector of the second switching transistor Q2 and the base of the first switching transistor Q1 is connected to a resistor R1 and a transistor Q3 as an auxiliary switch.
Is connected to the input terminal 1 via. The base of the transistor Q3 formed by a PNP transistor is connected to the ground via a resistor R5, and the base is connected to the primary winding N1 and the first switching transistor Q1 via a capacitor C5.
(Connection point (a)).

The self-excited oscillation operation of the circuit of FIG. 1 having such a configuration is as follows. When an input voltage is applied to the input terminal 1, the transistor Q3 in which the current path of the base current is formed by the resistor R5 receives a forward bias and turns on. Then, a current flows into the base of the first switching transistor Q1 via the transistor Q3 and the resistor R1, and the first switching transistor Q1 receives a forward bias and turns on. At this time, the second
The base between the base and the emitter of the switching transistor Q2 does not receive a forward bias necessary for turning on, and is turned off. This first switching transistor Q
When 1 is turned on, a linearly increasing current starts to flow through the primary winding N1 of the transformer T, and at the same time, the capacitor C3 is charged with the resistor R2 being at a high potential.

Here, the first switching transistor Q
The collector saturation current of 1 is determined by the magnitude of the current flowing through the base at that time. In the circuit of FIG. 1, when the transistor Q3 is on, the resistance is set to be substantially constant by the resistor R1. When the value of the current flowing through the primary winding N1 reaches the collector saturation current of the first switching transistor Q1, the current flowing through the primary winding N1 becomes constant, and at that moment, the potential difference between the terminals of the primary winding N1. Disappears. At this time, the capacitor C3 starts discharging, supplies a base current to the second switching transistor Q2, and makes the second switching transistor Q2 conductive. Then, the base current of the first switching transistor Q1 decreases and its collector current decreases, so that a flyback voltage is generated in each winding of the transformer T.

The flyback voltage generated in the primary winding N1 is applied to the base of the second switching transistor Q2 via the capacitor C3 and the resistor R2, and turns on the second switching transistor Q2. At the same time, the flyback voltage is also applied to the base of the transistor Q3 via the capacitor C5.
3 to the off state. When the second switching transistor Q2 is turned on and the transistor Q3 is turned off, the base potential of the first switching transistor Q1 is reduced, and at the same time, the first switching transistor Q1 is turned off.
Since the base current of No. 1 is cut off, the first switching transistor Q1 is turned off. While the second switching transistor Q2 is in the ON state, a current flows through the base of the second switching transistor Q2 via the primary winding N1, the capacitor C3, and the resistor R2.
3 is charged with the connection point (a) being at a high potential.

The decrease in the flyback voltage generated in the primary winding N1 of the transformer T and the decrease in the capacitance of the capacitors C3 and C5
, The base current of the second switching transistor Q2 decreases, and the reverse bias of the transistor Q3 decreases. Eventually, the second switching transistor Q2 shifts to the off state and the transistor Q3 shifts to the on state. When the second switching transistor Q2 is turned off and the transistor Q3 is turned on, current flows again into the base of the first switching transistor Q1 via the transistor Q3 and the resistor R1, and the first switching transistor Q1 is turned on. Move to.
Self-excited oscillation is performed by repeating such an operation process.

As can be seen from the above description of operation, the second switching transistor Q2 and the transistor Q3
They operate complementarily according to the change in the voltage at the connection point (a). Therefore, when the second switching transistor Q2 is off, the transistor Q3 is connected to the resistor R1 to supply the base current to the first switching transistor Q1.
To the second switching transistor Q
When the switch 2 is in the ON state, no current is supplied to the resistor R1.
Therefore, the unnecessary loss generated in the resistor R1 when the second switching transistor Q2 is in the ON state in the conventional circuit is reduced in the circuit shown in FIG.
Note that the present invention can be widely applied to a self-excited oscillation type switching power supply, and can be applied not only to the insulated power supply shown in FIG. 1 but also to a non-insulated power supply.

FIG. 2 shows a circuit of a second embodiment in which the present invention is applied to a non-insulated switching power supply. In FIG. 2, reference numeral 1 denotes an input terminal on the high potential side;
Indicates an output terminal on the potential side of the opposite polarity, and the input and output terminals on the reference potential side are both connected to the ground, so they are considered to be the same as the ground, and are not shown. Between a first switching transistor Q1 and a choke coil L1, and a connection point (b) between the first switching transistor Q1 and the choke coil L1 and an output terminal 3 by a PNP transistor connected in series between the input terminal 1 and the ground. The connected rectifier diode D1 and the smoothing capacitor C2 connected between the output terminal 3 and the ground constitute a power supply circuit generally known as a polarity inversion type converter.

The first switching transistor Q
A second switching transistor Q2 of a PNP transistor is provided, the emitter of which is connected to one of the emitters and the collector of which is connected to the base of the first switching transistor Q1. A series circuit of a resistor R2 and a capacitor C3 is connected between the base of the second switching transistor Q2 and the collector of the first switching transistor Q1, and a resistor R is connected between the base of the second switching transistor Q2 and the base of the first switching transistor Q1.
3 is connected. A resistor R1 and a control transistor Q4 are connected in series between a connection point between the collector of the second switching transistor Q2 and the base of the first switching transistor Q1 and the ground, and the base of the control transistor Q4 is connected via a capacitor C6. Connect to connection point (b).
A series circuit of a resistor R5 and a constant voltage diode DZ2 is connected between the input terminal 1 and the output terminal 3, and a connection point between the resistor R5 and the constant voltage diode DZ2 is connected to the base of the control transistor Q4.

The operation process of the self-excited oscillation operation of the circuit of FIG. 2 having such a configuration is basically the same as that of the circuit of FIG. However, the control transistor Q4 in FIG.
Originally, the base current of the first switching transistor Q1 is controlled to perform constant voltage control of the output voltage. Here, the control transistor Q4 is turned off by the voltage of the connection point (b) led by the capacitor C6 when the second switching transistor Q2 is on, and the constant voltage diode DZ2 is turned on when the second switching transistor Q2 is off. The base current of the first switching transistor Q2 is controlled by a signal corresponding to the output voltage to be led. That is, the control transistor Q4 of the circuit of FIG.
The function as the original control transistor and the function as the auxiliary switch in the present application are combined.

In the circuit diagrams of the embodiments shown in FIGS. 1 and 2, the impedance element for supplying a current to the base of the first switching transistor Q1 is a resistor R1, but, for example, a constant current element using a transistor element ( Circuit). Also, in the circuit diagrams of the embodiment shown in FIGS. 1 and 2, the first and second switching transistors Q
Although both 1 and Q2 are shown by the same junction type bipolar transistor, other types of transistor elements such as MOSFETs may be used. When a MOSFET is used, a resistor R1 is used as an impedance element.
Alternatively, a constant voltage element may be used. Further, the resistor R2 in FIGS. 1 and 2 may be omitted in some cases.
The power supply device to which the present invention is applied is not limited to the circuits having the configurations shown in FIGS.

[0023]

As described above, according to the present invention, the bias supply impedance element connected between the base of the first switching transistor and the input terminal of the power supply device or the reference potential point has the second characteristic. Is characterized in that an auxiliary switch performing a complementary operation is connected in series with the switching transistor. With this configuration, the first
A current flows through the impedance element that supplies a bias to the switching transistor of when the second switching transistor is off, and the current is cut off when the second switching transistor is on. Thus, unnecessary loss generated in the impedance element when the second switching transistor is in the on state is reduced, and a self-excited switching power supply device with high conversion efficiency can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a second embodiment of the self-excited switching power supply according to the present invention.

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

[Explanation of symbols]

Reference Signs List 1 input terminal 2 output terminal 3 output terminal (polarity inversion side) C2 smoothing capacitor C3 trigger capacitor C5 capacitor D1 rectifier diode DZ1 constant voltage diode DZ2 constant voltage diode L1 choke coil N1 primary winding N2 secondary winding Q1 1 switching transistor Q2 second switching transistor Q3 transistor as auxiliary switch Q4 control transistor R1 resistor T as bias supply impedance element T transformer

Claims (3)

[Claims] 1. A semiconductor device comprising: a first switching transistor and a second switching transistor that operate in a complementary manner, wherein current is intermittently interrupted by the first switching transistor, and via an inductance component connected in series to the first switching transistor. In a self-excited oscillation type switching power supply device configured to obtain an output voltage, the control terminal of the first switching transistor and the second
A current path connected between the connection point of the main current path of the switching transistor and the input terminal of the power supply, and for applying a forward bias to the first switching transistor when the second switching transistor is off. And an auxiliary switch that operates complementarily to the second switching transistor with respect to an impedance element that forms a current path through which a current flows when the second switching transistor is on. Are connected in series, a self-excited switching power supply device. 2. The auxiliary switch according to claim 1, wherein a control terminal of the auxiliary switch is a transistor connected to a connection point between the first switching transistor and the inductance component via a capacitive element. Self-excited switching power supply. 3. The self-excited switching power supply according to claim 1, wherein the impedance element is a resistor.