JPH0756635Y2 - Self-excited switching power supply circuit - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-excited switching power supply circuit, and more particularly to a self-excited switching power supply circuit for preventing destruction of switching elements and reducing switching noise.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of a conventional self-excited switching power supply circuit, wherein 1 is an input terminal and 2 is an output terminal. An oscillation circuit is formed on the primary winding N ₁ of the transformer T, and a rectifying / smoothing circuit is connected to the secondary winding N ₂ . Input to the terminal 1 is connected to the emitter and a resistor R ₇ of the capacitor C ₁ and the main switching transistor Q ₄ for smoothing, base resistor R ₈ and the capacitor C ₄ of the transistor Q ₄ is connected, the other resistor R ₈ The end is connected to the collector of the control transistor Q ₅ . The collector of the transistor Q ₄ is connected to the primary winding N ₁ of the transformer T. The secondary winding N ₂ of the transformer T is connected to the cathode of a rectifying diode D ₁ , and the anode thereof is connected to a smoothing capacitor C ₃ to form a rectifying and smoothing circuit. One end of the tertiary winding N ₃ of the transformer T is connected to the input terminal 1, and the other end is connected to the other end of the capacitor C ₄ . The base of the transistor Q ₅ is the capacitor C ₅
And the cathode of the constant voltage diode D ₅ and the other end of the resistor R ₇ . The anode of the constant voltage diode D ₅ which stabilizes the DC output is connected to one end of the smoothing capacitor C ₃ to stabilize the output. The other end of the capacitor _{C 1, C 3, C 5} , and primary and secondary windings N _1, of N ₂ and the other end of the emitter and the transformer T of the transistor Q ₅ is grounded together.

In the self-excited switching power supply circuit of FIG. 4, when power is applied to the input terminal 1, the capacitor C ₅ is charged, and the charging voltage turns on the transistor Q ₅ and turns on the switching transistor Q _4. Becomes The collector current from the transistor Q ₄ flows into the primary winding N ₁ of the transformer T, the induced electromotive force is generated in the primary winding N _1, the collector potential of the transistor Q ₄ are increased. An induced electromotive voltage is also generated in the secondary winding N ₂ and the tertiary winding N ₃ of the transformer T, and the induced electromotive voltage generated in the tertiary winding N ₃ further positively biases the transistor Q ₄ to deeply bias the tertiary winding N 3. _A current flows from ₃ to the base of the transistor Q ₄ via the capacitor C _4, and the collector current of the transistor Q ₄ rapidly reaches a saturation state and turns off. Then, a counter electromotive voltage is generated in the primary winding N _1, and at the same time, a counter electromotive voltage is also generated in the secondary winding N ₂ and the tertiary winding N ₃ .
The back electromotive force generated from the tertiary winding N ₃ reverse biases the transistor Q ₄ via the capacitor C ₄ . Therefore, the base current of the transistor Q ₄ suddenly decreases, and the transistor Q ₄ is turned off at once. On the other hand, the secondary winding N ₂
The voltage generated at the output terminal 2 is rectified by the diode D ₁ , and the negative DC output smoothed by the capacitor C ₃ is supplied from the output terminal 2 to the load, and the energy stored in the transformer T is rapidly reduced. When the energy stored in the transformer T decreases, the transistor Q ₅ draws the base current of the transistor Q ₄ again, the transistor Q ₄ becomes conductive, and the collector current of the transistor Q ₄ is supplied to the primary winding N _1. As a result, the oscillation operation is repeated.

[0004]

In the self-excited switching power supply circuit of FIG. 4, in order to reliably turn off the switching transistor Q ₄ , the tertiary winding N _{3 of the} transformer T is required.
The transistor Q ₄ is turned off by supplying the energy stored in the transistor Q _{4 as} a reverse bias current to the base of the transistor Q ₄ via the capacitor C ₄ , so that the tertiary winding N ₃ of the transformer T It is necessary to increase the induced energy. However, Taken together the reverse breakdown voltage characteristics between the emitter and base of the transistor Q _4, Q _5, it can not be assumed extremely large. Assuming a relatively small induced electromotive voltage and the tertiary winding N ₃ considering a reverse breakdown voltage of the transistor Q _4, completely will not be able to turn off the transistor Q ₄ for less stored energy, Transistor Q ₄
Remains in the ON state, a rush current may flow and the transistor Q ₄ may be destroyed. Therefore, the self-excited switching power supply circuit of FIG. 4 is generally used as a power supply for relatively small electric power of about 3 W, and has a drawback that it is not suitable for higher electric power.

On the other hand, in this type of self-excited switching power supply circuit, in order to stabilize the DC output, the diode D ₁
The output from the rectifying / smoothing circuit including the capacitor C ₃ and the capacitor C ₃ is fed back to the transistor Q ₅ via the constant voltage diode D ₅ to stabilize the output. The DC output of the self-excited switching power supply circuit, contains some ripples, the feedback current containing the ripple is supplied to the base of the transistor Q _5, the ripple contained in the output of the transistor Q ₅ phase Is a phase deviated from the phase of the ripple on the base side. This collector current is the transistor Q ₄
Since it is drawn as the base current of
The operation of ₄ will also be affected by the ripple. or,
Transistor Q ₅ is adapted to transistor Q ₄ by the sum current of the charging current of the capacitor C ₄ caused by the induced electromotive voltage generated in the collector current and the tertiary winding N ₃ of the transistor Q ₄ is turned on or off state Therefore, due to the phase shift between the charging current of the capacitor C _{4 and} the ripple current contained in the collector current of the transistor Q ₅ , a switching phenomenon of the transistor Q ₄ is intermodulated and a jitter phenomenon appears, and switching noise accompanied by the jitter is a direct current. There is a drawback of mixing in the output. It is an object of the present invention to provide a self-excited switching power supply circuit which is adapted to a relatively large power and has less jitter and noise.

[0006]

SUMMARY OF THE INVENTION A self-excited switching power supply circuit of the present invention is a transformer, in which a first switching transistor and a second switching transistor, which use the transformer as a load circuit, alternately operate. A multivibrator type oscillating circuit for supplying a pulse output to the rectifying circuit, a rectifying / smoothing circuit connected to the transformer, and a DC output from the rectifying / smoothing circuit to supply a base current to the second switching transistor. And a control circuit for holding the DC output at a predetermined potential.

[0007]

In the self-excited switching power supply circuit of the present invention, the DC current is output by controlling the base current of the switching transistor on the side where the transformer is not connected as a load circuit by feeding back the DC output from the rectifying and smoothing circuit. Can be adjusted to a predetermined value. AC feedback for oscillation and DC feedback for controlling the DC output to a predetermined value are performed through the base current of this switching transistor, which causes jitter. It is possible to obtain a DC output with little switching noise.

[0008]

FIG. 1 is a circuit diagram showing an embodiment of a self-excited switching power supply circuit according to the present invention.
A multivibrator type oscillator circuit 3 connected to the primary winding N ₁ of the transformer T, a rectifying / smoothing circuit 4 connected to the secondary winding N ₂ of the transformer T, and to keep the DC output at a constant value. The control circuit 5 of FIG. Input terminal 1 smoothing capacitor C ₁ and switching transistor Q
The emitters of ₁ and Q ₂ are connected to each other, and the transistor Q ₁
The primary winding N ₁ of the transformer T and the capacitor C on the collector of the
₂ is connected. Resistors R ₁ and R ₂ and the base of the transistor Q ₁ are connected to the collector of the transistor Q ₂ . The base of the transistor Q ₂ is resistors R _2, R _3, R ₄
It is connected to the connection point with. The other end of the resistor R ₃ is connected to the other end of the capacitor C ₂ and forms a time constant circuit. A diode D ₂ and a constant voltage diode D ₃ connected in series are connected between the base of the transistor Q ₂ and the input terminal 1. The cathode of a rectifying diode D ₁ is connected to the secondary winding N ₂ of the transformer T, and a smoothing circuit composed of a smoothing capacitor C ₃ is connected to its anode.
A rectifying / smoothing circuit 4 is formed. The anode of the constant voltage diode D ₄ is connected to the anode of the diode D ₁ , the resistor R ₅ is connected to the cathode thereof to form a constant voltage circuit, and a transistor is provided at the connection point of the resistor R ₅ and the constant voltage diode D _4. The emitter of Q ₃ is connected, the base of transistor Q ₃ is grounded through a resistor R ₆ , and its collector is connected to resistor R ₄ to form a control circuit 5 for holding the DC output at a constant potential. ing. The constant voltage diode D ₃ is for reverse bias protection of the emitter-base voltage of the transistor Q ₂ , and the diode D ₂ is forward-biased to the constant voltage diode D ₃ when the base of the transistor Q ₂ is forward biased. This is to prevent current from flowing and is not always necessary. Also, the capacitor C _1,
The other ends of C ₃ , resistors R _{1 and} R ₅ , and the primary and secondary windings N _{1 and} N ₂ of the transistor T are grounded.

Next, the operation of the self-excited switching power supply circuit of the present invention will be described with reference to FIG. When power is applied to the input terminal 1, the switching transistor Q ₂ remains off and the switching transistor Q ₁ is in operation. The collector current of the transistor Q ₁ is the transformer T
Is supplied to the primary winding N ₁ , the collector voltage of the transistor Q ₁ rises due to the induced voltage, and the capacitor C ₂ is charged. When the capacitor current of the transistor Q ₁ reaches a saturation state, the magnetic flux in the primary winding N ₁ does not increase, and the transistor Q ₁ turns off. Then is reverse charged capacitor C ₂ counter electromotive voltage is generated starting base current of the transistor Q ₂ flows through the primary winding N _1, the transistor Q ₂ is turned on, the transistor Q ₁ is turned off. When the capacitor C ₂ is charged by the base current of the transistor Q ₂ , its base voltage rises and the transistor Q ₂ is turned off again. When the transistor Q ₁ is off, a counter electromotive voltage is generated in the secondary winding N ₂ of the transformer T, rectified by the diode D ₁ , smoothed by the capacitor C ₃ , and a negative DC voltage V ₀ is output. It A constant voltage diode D ₄ and a resistor R ₅ connected in series are connected between the output terminal 2 and the ground. When the output voltage V ₀ is higher than the rated voltage of the constant voltage diode D ₄ , the terminal of the resistor R ₅ is connected. A voltage is generated between them. If the DC voltage V ₀ tries to exceed a predetermined potential, the resistance R ₅
A voltage is generated between the terminals of, and the voltage between the terminals causes a potential difference between the base and emitter of the transistor Q ₃ ,
The base current I _B flows into the base of the transistor Q ₃ via the resistor R ₆ , the transistor Q ₃ becomes conductive, and the base current I _B1 of the transistor Q ₂ is drawn as the collector current of the transistor Q ₃ via the resistor R _4. . Therefore,
Since a part of the base current I _B1 of the transistor Q ₂ is drawn into the transistor Q ₃ , the charging time of the capacitor C ₂ becomes long, so that the time until the transistor Q ₁ is turned on again can be lengthened. . That is, the timing of the switching of the transistor Q _1, Q ₂ is adjusted by controlling the base current I _B1 of the transistor Q _2. Further, when the DC output is a predetermined value, the potential difference between the base and emitter of the transistor Q ₃ is not generated, the timing of the switching of the transistor Q _1, Q ₂ is constant. In this way, the control circuit 5 controls the base current of the transistor Q ₂ to control the transistors Q _1, Q ₂
It is possible to keep the potential of the DC voltage V ₀ constant by controlling the time from the cutoff state to the operating state.

The DC output V ₀ of the self-excited switching power supply circuit of FIG. 1 can be expressed by the following equation. _{V 0 = - (V D4 +} V BE3 + R 6 · I B) ........................... (1) where, V _D4 is reverse voltage of the constant voltage diode D _4, V
_BE3 the base-emitter forward voltage of the transistor Q _3, R ₆ I _B is the terminal voltage of the resistor R _6. Also, I _B
Is a negligibly small value, and therefore the terminal voltage of the resistor R ₆ can be practically ignored.

FIG. 2 is a diagram showing another embodiment of the self-excited switching power supply circuit of the present invention. The control circuit 5 is different from that of FIG. 1, and the base of the transistor Q ₃ is a dividing resistor R ₇ , It is connected to the connection point of R ₈ . The DC voltage V ₀ of this embodiment can be set freely, and the DC voltage V ₀ can be expressed by the following equation. _{V 0 = - (V D4 +} V BE3) (1 + R 8 / R 7) .................. (2) where, R ₇ and R ₈ is the resistance of split resistor. According to the embodiment of the self-excited switching power supply circuit of FIG. 2, the output voltage can be arbitrarily adjusted by the voltage dividing ratio of the dividing resistors R ₇ and R ₈ .

The control circuit 5 shown in FIGS. 1 and 2 is a constant voltage circuit comprising a constant voltage diode D ₄ or a constant voltage element formed of a diode and a resistor R ₅ whose terminal voltage fluctuates based on the fluctuation of the DC output V _0. When a reference voltage source which is formed from the ground voltage or the dividing resistors R _7, R ₈ as the reference voltage,
It is composed of a transistor Q ₃ having a comparison function. The transistor Q ₃ may be composed of a comparison circuit such as a differential amplifier circuit. When a dividing resistor is used as the reference voltage source as in the embodiment of FIG. 2, the potential of the DC output V ₀ can be set arbitrarily. Of course, it is obvious that not only the dividing resistors but also the diodes may be used and they may be combined.

FIG. 3 shows another embodiment of the self-excited switching power supply circuit of the present invention. This embodiment has the polarity reversed from that of the embodiment of FIG. A DC voltage V _{0 of} is obtained. In the figure, transistors Q ₁ and Q forming the multivibrator type oscillation circuit 3 are shown.
Reference numeral ₂ is an NPN transistor, the anode side of the diode D ₁ of the rectifying / smoothing circuit 4 is connected to the secondary winding N ₂ , and the polarity of the constant voltage diode D ₄ is different from that of the embodiment of FIG. In the control circuit 5, the cathode of the constant voltage diode D ₄ is connected to the cathode of the diode D ₁ , the anode of the constant voltage diode D ₄ is connected to the resistors R ₅ and R ₇ and the emitter of the control transistor Q ₃ , and the transistor Q is connected. The base of ₃ is connected to the other end of the resistor R ₇ and the resistor R ₆ , the collector of the transistor Q ₃ is connected to the resistor R _4, and the other end is connected to the connection point of the resistors R ₂ and R ₃ . The operation is such that, when the output voltage V ₀ is higher than a predetermined potential, the transistor Q ₃ is biased by the voltage between the terminals of the resistors R ₅ and R ₇ , and the transistor Q ₃ draws the collector current I _C via the resistor R _4. As a result, the base current I _B1 of the transistor Q ₂ is controlled to control the DC potential of the output voltage V ₀ . Also, the tertiary winding N ₃ of the transistor T
It is also possible to obtain an output from the output terminals 2 _1, 2 ₂ to which is connected.

Of course, in the embodiments of the self-excited switching power supply circuit according to the present invention shown in FIGS. 1 to 3, the smoothing capacitors C ₁ and C ₂ connected to the input / output terminals 1 and ₂ are normally switched. It is built in the power supply, but the switching power supply is configured by excluding these parts. When using the switching power supply, smoothing capacitors C ₁ and C ₂ are added as external parts. It can happen.

[0015]

The self-excited switching power supply circuit of the present invention comprises a multi-vibrator type self-excited oscillation circuit in which two switching elements are alternately operated, and one switching element is connected to a transformer as a load. A rectifying / smoothing circuit is connected to the transformer, and the oscillator circuit is activated by applying AC feedback to the base current of the other switching element, and is supplied to the switching element to which the transformer is not connected. A stable DC output is obtained by controlling the base current via the control circuit according to the feedback amount of the DC output, and the ON / OFF timing of the switching element is supplied to the switch element. By controlling the current, the potential of the DC output can be adjusted. That is,
The self-excited switching power supply circuit according to the present invention controls the minute base current of the switching element to which the transformer is not connected, thereby providing the AC feedback for maintaining the oscillation.
Since the potential of the DC output can be controlled, the switching element is extremely effective even if it is used as a switching power source for relatively large electric power of 3 W or more.

Further, the self-excited switching power supply circuit of the present invention is designed to control the base current of the switching element paired with the switching element connected to the transformer, and also the AC feedback for maintaining the oscillation. Since it is superposed on the base of the switching element, the output side current is not modulated by the phase-shifted ripples and jitter is not generated. Therefore, according to the present invention, there is an advantage that a jitter noise peculiar to a self-excited switching power supply circuit is eliminated and a self-excited switching power supply circuit with less switching noise can be provided. Of course, the self-excited switching power supply circuit of the present invention has an advantage that the potential of the DC output can be easily set to an arbitrary value.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing another embodiment of the self-excited switching power supply circuit of the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the self-excited switching power supply circuit of the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional self-excited switching power supply circuit.

[Explanation of symbols]

1 Input Terminal 2 Output Terminal 3 Oscillation Circuit 4 Rectification Smoothing Circuit 5 Control Circuit T Transformer Q _1, Q ₂ Switching Transistor Q ₃ Control Transistor C _1, C _2, C ₃ Capacitor D _1, D ₂ Diode D _3, D ₄ Constant voltage diode N ₁ Primary winding N ₂ Secondary winding R _{1 to} R ₇ Resistance

Claims (3)

[Scope of utility model registration request] 1. A transformer, a first switching transistor having a primary winding of the transformer as a load circuit, and a second switching transistor which operates alternately with the first switching transistor to form a multivibrator. A transistor, a rectifying / smoothing circuit connected to the secondary winding of the transformer, and a constant voltage circuit connected to the rectifying / smoothing circuit,
A control circuit for shunting the base current of the second switching transistor to the constant voltage circuit according to the amount of feedback based on the DC output from the rectifying / smoothing circuit to control the base current to keep the DC output constant. A self-excited switching power supply circuit characterized by the above. 2. An emitter of a transistor is connected to a connection point between a series-connected constant voltage element constituting the constant voltage circuit and a resistor, the base of which is grounded through the resistor, and the collector of which is connected to the control circuit. The self-excited switching power supply circuit according to claim 1, wherein the self-excited switching power supply circuit is connected to the base of the second switching transistor via a resistor. 3. The control circuit has an emitter of a transistor connected to a connection point between a constant-voltage element and a resistor connected in series constituting the constant-voltage circuit, the base of which is an output terminal of the rectifying / smoothing circuit and a ground terminal. The utility model registration claim 1 characterized in that the collector is connected to the connection point of the divided resistors connected in between, and the collector is connected to the base of the second switching transistor via the resistor. Self-excited switching power supply circuit.