JP2003333838A - Self-excited switching power supply - Google Patents

Abstract

(57) Abstract: A self-excited switching power supply device capable of increasing a switching frequency with a simple configuration, suppressing an output ripple voltage, and contributing to downsizing is provided. SOLUTION: A second transistor Q2 is connected in series between an input terminal 1 and a control terminal of the first transistor Q1,
The third transistor Q3 is connected between the control terminal of the first transistor Q1 and the reference potential terminal 3. The fourth transistor is connected between the control terminal of the third transistor Q3 and the reference potential terminal 3.
Is connected. The voltage variation of the output terminal 2 is given to the control terminal of the third transistor Q3,
Is switched and rectified to obtain an output voltage. The fourth transistor Q4 is driven by a signal from the collector of the first transistor Q1, and the third transistor Q3 is also turned off while the first transistor Q1 is off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device for switching a DC current, converting it to a desired voltage for smoothing, and supplying it to an electronic device. .

[0002]

2. Description of the Related Art Conventionally, there is a self-excited oscillation system (hereinafter referred to as a self-excited system) as one of the driving systems for switching power supplies. The self-excited switching power supply device can be configured with a relatively simple circuit, and is mainly applied to a small capacity power supply device. As this self-excited switching power supply device, there is a circuit as shown in FIG.

The circuit shown in FIG. 5 has an input terminal 1 on the high potential side.
And a reference potential side terminal 3 which is the low potential side, a filter capacitor C1 is connected, a choke coil L1 and a rectifying diode D1 are connected in series to the input terminal 1, and the cathode of the diode D1 is output. It is connected to terminal 2. A smoothing output capacitor C2 is connected between the output terminal 2 and the reference potential terminal 3.

An npn-type transistor Q1 is connected in series with the choke coil L1 between the input terminal 1 and the reference potential terminal 3, and the emitter of the transistor Q1 is connected to the reference potential terminal 3. A resistor R1 and a pnp-type transistor Q2 are provided between the input terminal 1 and the base of the transistor Q1.
Are connected in series. The transistor Q2 has an emitter connected to the input terminal 1 via the resistor R1 and a collector connected to the base of the transistor Q1. The base of the transistor Q2 is connected to the connection point between the transistor Q1 and the choke coil L1 via the capacitor C6, and is also connected to the reference potential terminal 3 via the resistor R5. A diode D2 having a cathode connected to the input terminal 1 is connected between the base of the transistor Q2 and the input terminal 1.

Further, an npn-type transistor Q3 is provided between the base of the transistor Q1 and the reference potential terminal 3, the collector of the transistor Q3 is connected to the base of the transistor Q1, and the emitter is connected to the reference potential terminal 3. The base of the transistor Q3 is connected to the collector of the pnp type transistor Q5, and the emitter of the transistor Q5 is connected to the output terminal 2. Transistor Q
The base of No. 5 is connected to the output terminal 2 via the resistor R6, and the resistor R7 and the shunt regulator IC are connected together.
It is connected to the reference potential terminal 3 via the series circuit 1. The reference terminal of the shunt regulator IC1 is connected to its cathode through a series circuit of a capacitor C7 and a resistor R8, and is also connected between resistors R9 and R10 connected in series between the output terminal 2 and the reference potential terminal 3. Has been done.

Next, the operation of the self-excited switching power supply circuit shown in FIG. 5 will be described. First, when a DC voltage is applied to the input terminal 1, the transistor Q2 passes through the resistors R1 and R5.
The base current of the transistor Q2 flows and the transistor Q2 is turned on. When the transistor Q2 is turned on, its collector current flows into the base of the transistor Q1 to turn on the transistor Q1 and the collector potential of the transistor Q1 is lowered to the reference potential. As a result, a current flows through the choke coil L1 and energy is stored.

Further, in the steady operation state, a substantially constant control current I1 corresponding to the output voltage flows from the collector of the transistor Q5. The control current I1 reduces the base potential of the transistor Q3 lowered to a negative potential by transmitting the collector potential of the transistor Q1 via the capacitor C3 at the moment when the transistor Q1 is turned on.
While charging the capacitor C3, the voltage is raised to the on-voltage of the transistor Q3. When the base of the transistor Q3 reaches the ON voltage after a predetermined period required for this charging, the control current I1 flows into the base of the transistor Q3, and the transistor Q3 is turned ON.

When the transistor Q3 is turned on and begins to flow the collector current, the base current supplied from the transistor Q2 to the transistor Q1 is reduced and the base accumulated charge of the transistor Q1 is extracted. As a result, the collector current of the transistor Q1 cannot be increased, and the passing current of the choke coil L1 cannot be increased. Then, the polarity of the choke coil L1 begins to reverse, and the transistor Q1 shifts to the off state.

When the polarity of the choke coil L1 starts to reverse, the connection point a between the transistor Q1 and the choke coil L1 is a.
Rises, the voltage signal raises the base potential of the transistor Q2 via the capacitor C6, and the transistor Q2 shifts to the off state. Further, the voltage signal is given to the base of the transistor Q3 via the capacitor C3 to raise the base voltage to promote the turning on of the transistor Q3 and the turning off of the transistor Q1.

Then, after the transistor Q1 is turned off,
A current flows from the choke coil L1 to the output capacitor C2 via the diode D1, and the energy stored in the choke coil L1 is released. When the energy of the choke coil L1 is exhausted, the polarity of the choke coil L1 starts reversing again. When the potential at the connection point a between the transistor Q1 and the choke coil L1 drops, the voltage signal pulls down the base potential of the transistor Q2 via the capacitor C6, and the transistor Q2 shifts to the ON state. Further, the voltage signal pulls down the base potential of the transistor Q3 via the capacitor C3,
Turn off 3. When the transistor Q3 is turned off, the collector current of the transistor Q2 in the on state is changed to the transistor Q3.
1 and the transistor Q1 is turned on.

In this way, the circuit of FIG.
DC voltage is supplied to the output terminal 2 by rectifying the voltage fluctuation at the connection point a between the transistor Q1 and the choke coil L1 by the diode D1 and smoothing it by the output capacitor C2.

Here, stabilization of the output voltage will be described. For example, if the output current of the circuit shown in FIG. 5 is reduced,
The output voltage rises, the reference terminal potential of the shunt regulator IC1 rises, and the shunt regulator IC
The cathode current I2 of unity increases. As a result, the base current of the transistor Q5 increases, the collector current of the transistor Q5 increases, the charging speed of the capacitor C3 increases, and the off time of the transistor Q3 decreases as described above. Due to the decrease in the off time of the transistor Q3, the on time of the transistor Q1 is decreased and the output voltage is decreased. In the power supply circuit shown in FIG. 5, negative feedback is applied by the above operation, and the output voltage is stabilized.

Incidentally, the diode D2 and the diode D3
Are connected to prevent breakdown due to reverse voltage between the base and emitter of the transistors Q2 and Q3, respectively, and may be deleted depending on the input / output voltage conditions.

[0014]

However, in such a conventional self-excited switching power supply device as described above, after the transistor Q1 is turned off, the choke coil L1 exhausts current during the off period, and the above-mentioned operation is performed. The transistor Q3 is turned off, the base potential of the transistor Q1 rises, and the transistor Q1 is turned on. However, during the off period of the transistor Q1, the control current I1 always flows into the base of the transistor Q3, and the transistor Q3 is in the on state. After the polarity of the choke coil L1 is inverted, it takes time for the base Q3 of the transistor Q3 to be extracted before the transistor Q3 is turned off. Therefore, the collector current of the transistor Q2 flows into the collector of the transistor Q3 for a while, During that time, the base current of the transistor Q1 does not flow, and there is a problem that the on-timing of the transistor Q1 is delayed.

As a result, when it is attempted to switch the self-excited switching power supply device at a high frequency, the turn-on of the transistor Q1 is delayed as described above, the transistor Q1 is likely to be intermittently operated, and the intermittent operation causes an increase in output ripple voltage. Therefore, there is a limit to increase the switching frequency. If the switching frequency cannot be increased, the external size of the choke coil L1 is hindered from the viewpoint of magnetic saturation of the choke coil L1, which results in an obstacle to the miniaturization of the power supply device. Even when the steady-state switching frequency is set low, the circuit of the switching power supply device shown in FIG. 5 stabilizes the output voltage by increasing the switching frequency when the output current is decreased. There is also a problem in that the switching frequency rises, causing intermittent operation and increasing the output ripple voltage.

The present invention has been made in view of the above prior art, and is a self-excited switching power supply device that can increase the switching frequency with a simple structure, suppress the output ripple voltage, and contribute to downsizing. The purpose is to provide.

[0017]

According to the present invention, a choke coil and a first transistor are connected in series between an input terminal and a reference potential, and the input terminal or the reference potential and the first transistor are connected.
The impedance element and the second transistor are connected in series between the control terminals of the transistors, and the third transistor is connected between the control terminal of the first transistor and the reference potential or the input terminal. A signal is supplied from the connection point between the transistor and the choke coil to the control terminal of the second transistor, and the voltage fluctuation of the output terminal converted into the current signal is applied to the control terminal of the third transistor to supply the signal to the first terminal. What is claimed is: 1. A self-excited switching power supply device which switches a transistor to rectify a voltage at a connection point between the first transistor and a choke coil to obtain an output voltage, wherein a control terminal of a third transistor and a reference potential or an input terminal are provided. A fourth transistor is connected between the first transistor and the choke coil via a resistor or the like. Serial connected to the control terminal of the fourth transistor, and driving the fourth transistor by a signal from the collector of the first transistor, the first
In the self-excited switching power supply device, the third transistor is also turned off while the transistor is off.

A capacitance element is connected between the reference potential or the input terminal and the control terminal of the third transistor. A diode for promoting turn-off of the fourth transistor is connected between the control terminal of the fourth transistor and the collector of the first transistor. The impedance element is a resistor.

In the self-excited switching power supply device according to the present invention, after the third transistor draws the electric charge accumulated in the base of the first transistor and the first transistor is turned off, the fourth transistor turns on the third transistor. The base is short-circuited to the reference potential or the input potential, and the third transistor is also turned off after a predetermined time has passed since the first transistor was turned off. As a result, all the current flowing from the second transistor is injected into the base of the first transistor at the timing when the first transistor is turned on next, so that the turn-on of the first transistor is accelerated.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a self-excited switching power supply device according to an embodiment of the present invention. The same components as those of the conventional circuit shown in FIG. In the self-excited switching power supply device of this embodiment, a capacitor C1 is connected between an input terminal 1 on the high potential side and a terminal 3 on the reference potential side which is the low potential side, and a choke coil L1 and a diode D1 are connected to the input terminal 1. Are connected in series, and the cathode of the diode D1 is connected to the output terminal 2. An output capacitor C2 is connected between the output terminal 2 and the reference potential terminal 3.

An npn-type transistor Q1 is connected in series with the choke coil L1 between the input terminal 1 and the reference potential terminal 3, and the emitter of the transistor Q1 is connected to the reference potential terminal 3. A resistor R1 and a pnp-type transistor Q2 are provided between the input terminal 1 and the base of the transistor Q1.
Are connected in series. The transistor Q2 has an emitter connected to the input terminal 1 via the resistor R1, and a collector connected to the base of the transistor Q1. The base of the transistor Q2 is connected to the connection point between the transistor Q1 and the choke coil L1 via the capacitor C6, and is also connected to the reference potential terminal 3 via the resistor R5. A diode D2 having a cathode connected to the input terminal 1 is connected between the base of the transistor Q2 and the input terminal 1.

Further, an npn-type transistor Q3 is provided between the base of the transistor Q1 and the reference potential terminal 3, the collector of the transistor Q3 is connected to the base of the transistor Q1, and the emitter is connected to the reference potential terminal 3. The base of the transistor Q3 is connected to the collector of the pnp type transistor Q5, and the emitter of the transistor Q5 is connected to the output terminal 2. Transistor Q
The base of No. 5 is connected to the output terminal 2 via the resistor R6, and the resistor R7 and the shunt regulator IC are connected together.
It is connected to the reference potential terminal 3 via the series circuit 1. The reference terminal of the shunt regulator IC1 is connected to its cathode through a series circuit of a capacitor C7 and a resistor R8, and is also connected between resistors R9 and R10 connected in series between the output terminal 2 and the reference potential terminal 3. Has been done.

An npn-type transistor Q4 is provided between the base of the transistor Q3 and the reference potential terminal 3. The collector of this transistor Q4 is connected to the base of the transistor Q3, and its emitter is the reference potential terminal 3
It is connected to the. The base of the transistor Q4 is connected to the collector of the transistor Q1 via the resistor R11, and is also connected to the reference potential terminal 3 via the parallel circuit of the resistor R12 and the capacitor C8. further,
Between the base of the transistor Q4 and the collector of the transistor Q1 is provided a diode D4 whose anode is connected to its base and whose cathode is connected to its collector.

Next, the operation of the self-excited switching power supply device of this embodiment will be described with reference to FIG. Also in this circuit, the basic self-oscillation operation is similar to that of the circuit shown in FIG. 5 of the above-mentioned prior art. When a DC voltage is applied to the input terminal 1, the transistor Q2 passes through the resistors R1 and R5. A base current flows, turning on the transistor Q2. When the transistor Q2 turns on, its collector current flows to the base of the transistor Q1 and the transistor Q1
1 is turned on, and the collector potential of the transistor Q1 is lowered to the reference potential. As a result, the choke coil L1
An electric current flows through and energy is stored.

Further, in the steady operation state, a substantially constant control current I1 corresponding to the output voltage flows from the collector of the transistor Q5. The control current I1 reduces the base potential of the transistor Q3 lowered to a negative potential by transmitting the collector potential of the transistor Q1 via the capacitor C3 at the moment when the transistor Q1 is turned on.
While charging the capacitor C3, the voltage is raised to the on-voltage of the transistor Q3. When the base of the transistor Q3 reaches the ON voltage after a predetermined period required for this charging, the control current I1 flows into the base of the transistor Q3, and the transistor Q3 is turned ON.

When the transistor Q3 is turned on and the collector current begins to flow, the base current supplied from the transistor Q2 to the transistor Q1 is reduced and the base accumulated charge of the transistor Q1 is extracted. As a result, the collector current of the transistor Q1 cannot be increased, and the passing current of the choke coil L1 cannot be increased. Then, the polarity of the choke coil L1 begins to reverse, and the transistor Q1 shifts to the off state.

When the polarity of the choke coil L1 begins to reverse, the connection point a between the transistor Q1 and the choke coil L1 is a.
Rises, the voltage signal raises the base potential of the transistor Q2 via the capacitor C6, and the transistor Q2 shifts to the off state. Further, the voltage signal is given to the base of the transistor Q3 via the capacitor C3 to raise the base voltage to promote the turning on of the transistor Q3 and the turning off of the transistor Q1.

Then, after the transistor Q1 is turned off,
A current flows from the choke coil L1 to the output capacitor C2 via the diode D1, and the energy stored in the choke coil L1 is released. The operation up to this point is similar to that of the circuit shown in FIG.

After the transistor Q1 is turned off, in the circuit of this embodiment, the collector potential of the transistor Q1 rises to the potential of the output terminal 2 plus Vf of the diode D1. This voltage signal raises the base voltage of the transistor Q4 to a potential at which the transistor Q4 can be turned on after a delay time set by the resistors R11, R12 and the capacitor C8. Then, the transistor Q4 is turned on, the base potential of the transistor Q3 is lowered, and the transistor Q3 is turned off. That is, after the transistor Q3 turns off the transistor Q1, the transistor Q3 also turns off after a set delay time.

After that, when the current flows from the choke coil L1 to the output capacitor C2 via the diode D1 during the off period of the transistor Q1 and the energy stored in the choke coil L1 is exhausted, the choke coil L1 is discharged.
The polarity of 1 starts reversing again. When the potential at the connection point a between the transistor Q1 and the choke coil L1 drops, the voltage signal pulls down the base potential of the transistor Q2 via the capacitor C6, and the transistor Q2 shifts to the ON state.

In the circuit of this embodiment, the transistor Q
2 starts to turn on, the collector current flowing through the transistor Q2 is different from that of the conventional circuit of FIG.
Is not supplied to the transistor Q1 and is supplied to the base of the transistor Q1, so that the transistor Q1 is rapidly turned on.

In this way, the circuit of FIG. 1 self-oscillates at a high speed, rectifies the voltage fluctuation at the connection point a between the transistor Q1 and the choke coil L1 by the diode D1 and smoothes it by the output capacitor C2, and thereby the output terminal Supply DC power to 2.

Here, the diode D4 is for rapidly lowering the base potential of the transistor Q4 when the transistor Q1 is turned on, so that the transistor Q4 is quickly turned off. Further, the diode D2 and the diode D3 are connected to prevent destruction due to a reverse voltage between the base and emitter of the transistor Q2 and the transistor Q3, as described in the conventional circuit of FIG.

Regarding the stabilization of the output voltage, as shown in FIG.
When the output current is decreased, the output voltage increases, the reference terminal potential of the shunt regulator IC1 increases, and the cathode current I2 of the shunt regulator IC1 increases, as in the circuit of FIG. As a result, the transistor Q5
, The collector current of the transistor Q5 increases, the charging speed of the capacitor C3 increases, and the off time of the transistor Q3 decreases as described above. Due to the reduction of the off time of the transistor Q3, the transistor Q1
The ON time of is reduced and the output voltage is reduced. Even in the power supply circuit shown in FIG. 1, negative feedback is applied by the above operation, and the output voltage is stabilized.

By the above operation, the turn-on of the transistor Q1 can be accelerated, so that the intermittent operation during high frequency switching can be suppressed, the switching frequency can be increased, and the device can be miniaturized. Further, even if the switching frequency rises when the output current is low, the intermittent operation can be suppressed and the increase of the output ripple voltage can be suppressed.

Next, a second embodiment of the present invention will be described with reference to FIG. Here, the same configurations as those of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted. The circuit of the switching power supply device shown in FIG. 2 is obtained by removing the capacitor C3 and the diode D3 in the first embodiment and connecting a capacitor C4 between the base of the transistor Q3 and the reference potential. The capacitor C4 is the capacitor C3
Similarly, it has a function of setting the timing at which the transistor Q3 is turned on.

In the operation of the circuit of the second embodiment, the transistor Q3 is turned off after the set delay time in the period in which the transistor Q1 is turned off by the transistor Q3, as in the first embodiment. After that, the choke coil L1 exhausts the current during the off period of the transistor Q1, and the voltage signal whose polarity is inverted enters the base of the transistor Q2 via the capacitor C6, and the transistor Q2
Is turned on, all the collector current flowing through the transistor Q2 is supplied to the base of the transistor Q1.
Therefore, the transistor Q1 can be rapidly turned on. This operation is similar to that of the first embodiment, and like the above embodiment, it is possible to suppress intermittent oscillation, increase the switching frequency, and downsize the power supply device.

Further, in this embodiment, the capacitor C3
By eliminating the above, the diode D3 for preventing breakdown due to the reverse voltage between the base and emitter of the transistor Q3 in the first embodiment becomes unnecessary. Therefore, in the case of the input / output condition that the diode D3 for preventing the breakdown due to the reverse voltage must be provided in the circuit configuration of FIG. 1, the circuit shown in FIG. 2 is preferable.

Next, a third embodiment of the present invention will be described with reference to FIG. Here, the same configurations as those of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted. The circuit of the switching power supply device shown in FIG. 3 applies the present invention to a polarity reversal type power supply. In this embodiment, the transistors Q1-Q5 are modified as follows with respect to the circuit of FIG. The transistor Q1 is a pnp type, the transistor Q2 is an npn type, the transistor Q3 is a pnp type,
The transistor Q4 is a pnp type, and the transistor Q5 is an np type.
It is replaced by an n-type transistor.

Then, from the output terminal 2, an output whose polarity is inverted is output. The base of the transistor Q5 is connected to the reference potential terminal 3, and the transistor Q1 is turned on / off by the control current I1 as in the first embodiment. In this operation, the capacitor C3 is charged, and the transistor Q3 is turned on to turn off the transistor Q1. After turning off this transistor Q1, the transistor Q
The transistor Q3 is also turned off when the transistor 4 is turned on. As a result, the collector current that starts to turn on in the transistor Q2 and flows in the transistor Q2 does not flow in the transistor Q3, but is entirely supplied from the base of the transistor Q1.
The transistor Q1 is rapidly turned on. Therefore, also in this embodiment, the same effect as the first embodiment can be obtained.

Next, a fourth embodiment of the present invention will be described with reference to FIG. Here, the same configurations as those of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted. In the circuit of the switching power supply device shown in FIG. 4, the capacitor C3 and the diode D3 in the third embodiment are deleted, and the capacitor C4 is connected between the base of the transistor Q3 and the input terminal 1. The capacitor C4 is a capacitor C
Similar to the function 3, the function of setting the timing at which the transistor Q3 is turned on is performed.

In the operation of the circuit of the fourth embodiment, the transistor Q3 is turned off after the set delay time in the period in which the transistor Q1 is turned off by the transistor Q3, as in the third embodiment. After that, the choke coil L1 exhausts the current during the off period of the transistor Q1, and the voltage signal whose polarity is inverted enters the base of the transistor Q2 via the capacitor C6, and the transistor Q2
Is turned on, the collector current flowing through the transistor Q2 is entirely supplied from the base of the transistor Q1. Therefore, the transistor Q1 can be rapidly turned on. This operation is the same as in the third embodiment, and similarly to the above-described embodiment, it is possible to suppress intermittent oscillation, increase the switching frequency, and downsize the power supply device.

Further, in this embodiment, the capacitor C3
By eliminating the above, the diode D3 for preventing breakdown due to the reverse voltage between the base and emitter of the transistor Q3 in the third embodiment becomes unnecessary. Therefore, the circuit shown in FIG. 4 is preferable under the input / output conditions in which the diode D3 for preventing breakdown due to the reverse voltage must be provided in the circuit configuration of FIG.

The self-excited switching power supply device of the present invention is not limited to the above embodiment, and various types of transistors can be used as the transistors.
Any circuit having a similar function may be used. Other electronic elements can be selected as appropriate, and the circuit configuration can be appropriately changed.

[0045]

According to the self-excited switching power supply device of the present invention, a transistor is connected between the base of the third transistor for turning off the first transistor, which is a switching element, and the reference potential or the input terminal, and the control signal is supplied to the first transistor. By obtaining from the collector of the first transistor, the turn-on of the first transistor can be accelerated, the switching frequency can be increased, and the intermittent oscillation can be suppressed. A choke coil smaller than this can be used, and as a result, a small switching power supply device can be obtained. Moreover, since the intermittent operation at low output current can be suppressed, the output ripple voltage at low output current can be reduced.

[Brief description of drawings]

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

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

FIG. 3 is a schematic circuit diagram of a self-excited switching power supply device according to a third embodiment of the present invention.

FIG. 4 is a schematic circuit diagram of a self-excited switching power supply device according to a fourth embodiment of the present invention.

FIG. 5 is a schematic circuit diagram of a conventional self-excited switching power supply device.

[Explanation of symbols]

1 input terminal 2 output terminal 3 reference potential terminals C1, C2, C3, C4, C6, C7, C8 capacitors D1, D2, D3, D4 diode IC1 shunt regulator L1 choke coil R1, R5, R6, R7, R8, R9, R10, R1
1, R12 resistors Q1, Q2, Q3, Q4, Q5 transistors

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hayato Nakatsubo             1-643 Kamiakae-cho, Toyama City, Toyama Prefecture             -In cell corporation F-term (reference) 5H730 AA10 AA15 AS01 AS04 BB14                       BB52 DD02 DD42 EE07 FD01                       FD22 FG07

Claims (4)

[Claims] 1. A choke coil and a first transistor are connected in series between an input terminal and a reference potential, and an impedance element and a second transistor are connected in series between the input terminal or the reference potential and a control terminal of the first transistor. Connected,
From the connection point of the first transistor and the choke coil to the second
A signal is supplied to the control terminal of the first transistor, the third transistor is connected between the control terminal of the first transistor and the reference potential or the input terminal, and the voltage fluctuation of the output terminal converted into the current signal In the self-excited switching power supply device which is applied to the control terminal of the transistor and rectifies the voltage at the connection point of the first transistor and the choke coil to obtain the output voltage, the control terminal of the third transistor and the reference potential or the input terminal A fourth transistor is connected between the first transistor and the choke coil, and the fourth transistor is connected to the control terminal of the fourth transistor.
A self-excited switching power supply device characterized in that the fourth transistor is driven by a signal from the transistor to turn off the third transistor. 2. The reference potential or input terminal and the third terminal
The self-excited switching power supply device according to claim 1, wherein a capacitive element is connected between the transistor and the control terminal of the transistor. 3. The diode for promoting turn-off of the fourth transistor is connected between the control terminal of the fourth transistor and the collector of the first transistor. Self-excited switching power supply. 4. The self-excited switching power supply device according to claim 1, wherein the impedance element is a resistor.