JPH0531385B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a self-oscillation type switching power supply device used in various electronic devices.

BACKGROUND ART Conventionally, this type of self-oscillation type switching power supply device has a configuration as shown in FIG. In FIG. 4, 1 is a rectifying and smoothing circuit that rectifies and smoothes a commercial AC voltage to convert it into a DC voltage V _IN . 2 is a switching transformer with input winding 21 and output winding 22.
and bias windings 24 and 25 connected in series.

3' is a switching transistor whose collector is connected to the output electrode of the rectifying and smoothing circuit 1 via the input winding 21, and whose emitter is connected to the same negative electrode, and which turns on and off repeatedly. 41' is a resistor connected in series with the positive electrode of the rectifying and smoothing circuit 1 and the base of the switching transistor 3 to supply a starting current; 11 is the base of the switching transistor 3 and the bias winding 2;
This is a drive circuit that is connected in series to one end of 4 and sets the base current. 80 is a reverse bias transistor whose collector is connected to the base of the switching transistor 3 and whose emitter is connected to one end of the bias winding 25; 70 is a reverse bias transistor whose emitter is connected to the connection point between the bias windings 24 and 25; A control transistor 65' whose base is connected to the base of the reverse bias transistor 80 via a resistor 61' and whose emitter is connected via a capacitor 69' has an anode connected to the bias winding 25 and the reverse bias transistor 80. A diode is connected to the connection point of the emitter and has its cathode connected to the connection point of the capacitor 69' and the base of the control transistor 70, allowing the charging current of the capacitor 69' to flow and cutting off the discharging current.

It is connected in series with the resistor 68 and the Zener diode 67, and in parallel with the diode 65', allowing the discharge current of the capacitor 69' to flow.

The input side and output side are isolated and insulated by a photocoupler, and the collector of the input side photodetector transistor 81 is connected to a capacitor 69' and a control transistor 70.
The emitter is connected to the connection point of the base of the bias winding 25 and the emitter of the reverse bias transistor 80, and the output side light emitting diode 81' is connected to the detection circuit 13. 12 is an output rectifying and smoothing circuit connected to the output winding 22, and DC
Provides output. The DC output is connected to a detection circuit 13 to detect the DC output voltage.

In the conventional circuit configured as above,
The operation will be explained below.

First, when a commercial voltage is applied to the AC input, a DC voltage V _IN is generated in the rectifier and smoothing circuit 1, and current flows to the base of the switching transistor 3' via the resistor 41', and the switching transistor 3' is turned on. A voltage is applied to the primary winding 21, and an induced voltage proportional to this voltage is generated in the bias winding 24, and the base current of the switching transistor 3' is further increased via the drive circuit 11, thereby increasing the on-period. becomes. During the on period, the collector current of the switching transistor 3' increases linearly with a slope determined by the inductance of the primary winding 21, and excites the switching transformer 2. On the other hand, an induced voltage proportional to the input voltage is also generated in the bias winding 25, and the capacitor 69' and the resistor 6
8 and the Zener diode 67, the voltage across the capacitor 69' decreases to a voltage that forward biases the emitter and base of the control transistor 70. This voltage turns on the control transistor 70, and the reverse bias transistor 80 is turned on via the resistor 61'.
The induced voltage of the bias winding 25 is applied to the base of the transistor 3', and the reverse bias transistor 80 turns on, rapidly drawing the base current of the switching transistor 3', reverse biasing the base of the switching transistor 3', and turning it off. let During the off period T _OFF , the induced voltage generated in the bias winding 24 generates a voltage in a direction that reverse biases the base of the switching transistor 3', and
The rectifying and smoothing circuit 12 outputs the excitation energy accumulated in the switching transformer 2 from the output winding 22.
to the DC output. When the excitation energy disappears, the ringing voltage generated by the inductance and distributed capacitance of the switching transformer 2 generates an induced voltage in the bias winding 24 in the direction of forward biasing the base of the switching transistor 3' again, so that the same switching occurs. Transistor 3' is turned on.

Furthermore, during the off period, the voltage across the bias winding 25 is such that an induced voltage is generated in the direction of making the connection point with the bias winding 24 a negative voltage. capacitor 69' to reverse bias
is charged, and the control transistor 20 is turned off. The charging voltage of the capacitor 69' is determined by the turns ratio of the output winding 22 and the bias winding 25, that is,
The voltage is proportional to the DC output voltage. Thereafter, the above-described operation is repeated to supply the output voltage. When the DC output voltage reaches the voltage set by the detection circuit 13, the detection circuit 13 operates and the photocoupler 8
1 and 81' are activated, and the charge of the capacitor 69' charged during the off period is transferred to the series circuit of the resistor 66 and the Zener diode 67 during the on period.
The light is discharged through the parallel circuit of the light-receiving transistor 81. As a result, the discharge time of the capacitor 69' is
Since the discharge occurs in a faster time than the discharge time due to only the resistor 68 and the Zener diode 67 described above, the on-period is shortened, the duty ratio changes, and the output voltage is kept constant. That is, the DC output voltage is in a controlled state.

In FIG. 5, a shows the collector-emitter voltage V _CE of the switching transistor 3', b shows the voltage V _CF across the capacitor 69', and c shows the base-emitter voltage V _BE80 of the reverse bias transistor 80. .

Problems to be Solved by the Invention In such a conventional configuration, the on-period is the time during which the voltage across the capacitor 69', _VCF , discharges from the flyback voltage of the bias winding to the negative base-emitter voltage; What is determined is the value of the current flowing through the light-receiving transistor 81 of the photocoupler, and since this current value is finite, there is inevitably a minimum value in the on period. That is, when the output current decreases and the on-period to be controlled reaches the minimum limit value, there is a problem that normal control becomes impossible.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and aims to provide a self-oscillation type switching power supply device that eliminates the minimum value of the on-period and has a wide stable control operation range.

Means for Solving the Problem In order to solve this problem, the present invention provides a bias circuit that biases a control circuit by rectifying and smoothing the flyback voltage induced in the bias winding during the OFF period of the main switching element; a pulse generating circuit that detects the flyback voltage and sends out a first pulse inverted in synchronization with the flyback voltage; and a pulse generating circuit that charges a capacitor to a first specified voltage value during an off period and induces voltage in the bias winding during an on period. a charging/discharging circuit that discharges the capacitor to a forward voltage of a negative potential through at least a resistor; and comparing the voltage across the capacitor with a second specified voltage value set lower than the first specified voltage value. a first comparator circuit that becomes H when the second specified voltage value is low; an error amplification circuit that detects the output voltage and generates a third specified voltage value in accordance therewith; and the third specified voltage value. a second comparator circuit that compares the voltage value with the voltage across the capacitor and becomes H when the third specified voltage value is low; The configuration includes an AND circuit that sends out a second pulse that is the logical product of the outputs of the comparison circuit, and a drive circuit that amplifies the second pulse to drive the main switching element.

Effect With this configuration, the discharge time of the capacitor, which is the ON period, is determined by the voltage across the capacitor decreasing from the first specified voltage value and the third specified voltage value determined to stabilize the output voltage. is determined by the time it takes for the voltage across the capacitor to fall below the third specified voltage value. That is, the third
If the specified voltage value of is as close as possible to the first specified voltage value, the on period will also be as close as possible to zero, and in principle, there is no minimum value of the on period,
This allows a wide range of stable control operation.

Embodiment FIG. 1 is a circuit diagram of a self-oscillation type switching power supply device according to an embodiment of the present invention. In FIG. 1, 1 is a rectifying and smoothing circuit that rectifies and smoothes a commercial AC voltage to convert it into a DC voltage. 2 is a switching transformer with an input winding 21, an output winding 22,
It has a bias winding 23. Reference numeral 3 designates a switching transistor whose collector is connected to the positive electrode of the rectifying and smoothing circuit 1 via the input winding 21, and whose emitter is connected to the negative electrode of the rectifying and smoothing circuit 1, and which repeatedly turns on and off. 4 is a bias circuit, which is composed of a diode 42 and a capacitor 43 that rectify and smooth the flyback voltage V _FB induced in the bias winding 23, and a starting resistor 41 that charges the capacitor 43 at startup (hereinafter, the potential of the capacitor 43 is called the bias voltage). Reference numeral 5 designates a pulse generating circuit which is inputted from one end of the bias winding 23 through a resistor 51 to an inverting amplifier circuit 52, and sends out a pulse _V5 inverted in synchronization with the flyback voltage _VFB . 6 is a charging/discharging circuit, which connects a diode 66 and a Zener diode 6 from one end of the bias winding 23.
7. A charging circuit consisting of a transistor 65, a resistor 63, and a Zener diode 64, which is connected to the capacitor 69 via a discharging circuit consisting of a series circuit of a resistor 68, and charges the capacitor 69 from a bias voltage section to a specified value _V1 . The charging circuit is connected to the ON period of the switching transistor 3 (hereinafter referred to as the ON period).
It is composed of a resistor 61 and a transistor 62, which are configured to stop the signal. 7 is a comparator circuit that compares the potential V _CF of the capacitor 69 and the specified value V ₂
It becomes H level when V _CF <V ₂ . 8 is an error amplification circuit, and a detection circuit 13 on the output side
detects the DC output voltage and photodiode 8
1', a current flows through the phototransistor 81, and a specified voltage is applied to the resistor 82.
Generate V ₃ . 9 is a comparison circuit that compares the potential V _CF of the capacitor 69 with the specified voltage V ₃ and determines that V _CF > V ₂
It becomes H level when . 10 is an AND circuit which sends out the logical product of the outputs of the pulse generating circuit 5, the comparator circuit 7, and the comparator circuit 9. 11 is the drive circuit,
The output of the AND circuit 10 is amplified and the switching transistor 3 is turned on and off. 12 is a rectifying and smoothing circuit consisting of a diode 14 and a capacitor 15;
The flyback voltage induced in the output winding 22 is rectified and smoothed to provide a DC output voltage.

In Fig. 2, a is the drain-source voltage V _DS of the switching transistor 3, and b is the bias winding 2.
3, _c is the output V ₅ of the pulse generation circuit 5, d is the waveform of V _CF with V ₁ , V ₂ , and V ₃ , and e is the output voltage V of the AND circuit 11. _OUT
shows.

The operation will be explained below using FIGS. 1 and 2.
First, when AC input is applied, the rectifier and smoothing circuit 1 generates a DC voltage V _IN which is passed through the resistor 41 to the capacitor 4.
3 is charged and a bias voltage is generated. At this time, the bias winding voltage is 0V, so _V5 becomes H, but since no voltage is also output to _VCF , the comparator circuit 7
The output of the drive circuit 11 becomes L, and the output of the drive circuit 11 becomes L.
Then, the switching transistor 3 is off.
However, once the bias voltage is applied, V _CF rapidly
Charged to V ₁ , comparison circuits 7 and 9 also operate,
All inputs to the AND circuit 10 become H, and the switching transistor 3 is also driven and turned on. When turned on, the transistor 6
A base current flows through the transistor 2, turning on the transistor 62, and reverse biasing the transistor 65, turning it off. When the transistor 65 turns off, the capacitor 6
The charging current to 9 is cut off, and at the same time, due to the negative potential forward voltage V _FW generated in the bias winding 23, a discharge current flows through the resistor 68, the Zener diode 67, and the diode 66, and V _CF decreases. do. The diode 66 cuts off the charging path of the capacitor 69 due to the flyback voltage V _FB during the off period, and the Zener diode 67 is for correcting the discharge time constant of the capacitor 69 due to the input voltage V _IN . The base-emitter voltage of the transistor 65 is V _BE65 , the capacitance of the capacitor 69 is C _F ,
The Zener voltage of Zener diode 64 is V _Z64 ,
The Zener voltage of Zener diode 67 is V _Z67 ,
Assuming that the forward voltage of the diode 66 is V _D66 , the resistance value of the resistor 68 is R ₆₈ , the number of turns of the input winding 21 is N ₂₁ , and the number of turns of the bias winding 23 is N ₂₃ , from on to t
V _CF after seconds can be expressed by the following formula.

V ₁ = V _Z64 −V _BE65 , V _FW = N ₂₃ /N ₂₁ V _IN V _CF = V ₁・e ^-t/CFR68 + (N ₂₃ /N ₂₁ V _IN −V _D66 −V _Z64 ) (e
^-t/CFR68 -1) When V _CF eventually falls below the potential of V ₂ or V ₃ , the output of comparator circuit 7 or 9 is inverted and becomes L, so the output V _GS of drive circuit 11 also becomes L, and the switch The switching transistor 3 is turned off. When turned off, the transistor 62 has no base current and is turned off. When the transistor 62 is turned off, the transistor 65 is supplied with base current through the resistor 63.
turns on and capacitor 69 is rapidly charged to _V1 . The outputs of the comparison circuits 7 and 9 both become H, but there is a flyback voltage in the bias winding 23.
Since V _FB is generated, the output V ₅ of the pulse generation circuit 5 becomes L, and the excitation energy of the switching transformer 2 stored during the on period is transferred from the output winding 22 to the rectifier and smoothing circuit 12 to DC. emitted to the output. When the excitation energy disappears, due to the ringing voltage generated by the inductance and distributed capacitance of the switching transformer 2, V _FB disappears in the bias winding 23, the pulse generation circuit 5 is inverted, V ₅ becomes H, and V _GS becomes H, and the switching transistor 3 is turned on again. By repeating the above operation, a DC output voltage is supplied.
The DC output voltage is detected by the detection circuit 13 on the output side, and the information is fed back by the photocouplers 81' and 81. That is, when the DC output voltage increases, the amount of light from the light emitting diode 81' increases,
Increase the current value of the light receiving transistor 81, and
The on-period is shortened by raising the potential V ₃ of the second circuit and shortening the period during which the comparator circuit 9 is at H, thereby reducing the DC output voltage. DC
When the output voltage decreases, the operation is opposite to that described above, and by lengthening the on period, the DC output voltage increases. In other words, the DC output voltage is in a controlled state. This circuit also has an overcurrent protection function that limits the maximum on-period. In other words, the control works to lengthen the on period, and V ₃
Even if V CF becomes low and becomes less than V ₂ , when V _CF becomes less than V ₂ by comparison circuit 7, the off period begins. The maximum on-period T ^MAX _ON is expressed by the following formula.

T ^MAX _ON =C _F・R ₆₈・lnN ₂₃ /N ₂₁・V _IN
−V _D66 −V _Z67 +V ₁ /N ₂₃ /N ₂₁・V _IN −V _D66 −V _Z67 +V In formula ₂ , all values except V _IN are fixed values, and T ^MAX _ON is V _IN
It can be seen that it is uniquely determined by . Also, as already mentioned, if V _Z67 is selected appropriately, the variation in T ^MAX _ON due to V _IN can be corrected by the necessary amount.

FIG. 3 shows another embodiment of the present invention, which shows the bias circuit 4, pulse generation circuit 5, charge/discharge circuit 6, comparison circuits 7 and 9, error amplifier 8,
This is a control circuit corresponding to the AND circuit 10. Among the components, those corresponding to those in FIG. 1 are labeled with the same numbers. The bias circuit connects V _FB to diode 4
After rectification and smoothing using 2 and a capacitor 43, a bias voltage is generated by a DC stabilizing circuit consisting of a transistor 44, a resistor 45, and a Zener diode 46. Furthermore, specified voltage values V ₁ and V ₂ are created by resistors 16, 17, 18 and transistor 48, and transistor 48 constitutes a current mirror with transistors 49 and 79, and transistor 49 forms a current mirror.
Current mirror 47 consisting of PNP transistor
Determine the current value. In the pulse circuit 5, a transistor 56 receives V _FB via a resistor 51, converts it into a pulse synchronized with V _FB using a Schmitt trigger circuit including transistors 57, 58, and a resistor 53, and inverts it using a transistor 59. Transistor 54,5
5 prevents the base potential of the transistor 56 from becoming a negative potential due to the forward voltage during the on period. The charging/discharging circuit 6 charges the capacitor 69 to a specified voltage value V ₁ through the transistors 66' and 65 during the off period, and turns on the transistor 62 with the base current flowing through the resistor 61 during the on period to turn on the transistor. 65 is turned off, the charging current is cut off, and the voltage is discharged to V _FW (=N ₂₃ /N ₂₁ V _IN ) via the transistor 64', resistor 68, and Zener diode 67. During the off period, transistors 63' and 64'
In addition to preventing charging of capacitor 69 by V _FB ,
It has the role of fixing the potential at the connection point between the emitter of the transistor 64' and the resistor 68 to 0V during the on period. With this circuit configuration, V _CF during the on period is expressed by the following equation.

V _CF =V ₁ −N ₂₃ /N ₂₁・V _IN −V _Z67 /C _F・R ₆₈・t The error amplification circuit 8 is connected to the phototransistor 81 via the photocoupler by transistors 83 and 84 forming a current mirror. The information of the DC output voltage transmitted as the current value is converted to the voltage across the resistor 82.
Convert to _V3 . Comparison circuit 7 includes comparison circuit 9 shown in FIG. Transistors 72, 73, and 74 receive and compare V ₂ , V ₃ , and V _{4 ,} respectively, and when V _CF <V ₂ or V _CF <V ₃ , a current mirror consisting of transistors 75 and 76 operates, transistor 7
Supply a base current to 7 to turn it on. The collector of the transistor 77 is common to the collector of the transistor 59, and becomes H only when both are off, so that the transistor 77 has a collector similar to that of the AND circuit 10 in FIG. 1. With the above configuration, the circuit operates in the same way as the circuit shown in FIG. 1, and stably controls the DC output voltage. Also, the overcurrent operation is the same, and the maximum on time
T ^MAX _ON is expressed by the following formula.

T ^MAX _ON =C _F・R ₆₈・V ₁ −V ₂ /N ₂₃ /N ₂₁・V _IN −V _Z67Effects of the Invention As described above, the present invention is capable of varying the pulse width depending on the discharge time of the capacitor. In the self-excited oscillation type switching power supply device, the discharge time, that is, the on-period, is determined by comparing the voltage across the capacitor with a specified voltage value.
In principle, it is possible to make the pulse width infinitely small, and the control width can be widened, which has great practical effects.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a self-oscillation type switching power supply device according to one embodiment of the present invention, FIG. 2 is a waveform diagram of the main part thereof, FIG. 3 is a circuit diagram of the main part of another embodiment, and FIG. The figure is a conventional circuit configuration diagram, and FIG. 5 is a waveform diagram of essential parts of the conventional circuit. 1... Rectifying and smoothing circuit, 2... Switching transformer, 3... Switching transistor, 4...
Bias circuit, 5... Pulse generation circuit, 6... Charge/discharge circuit, 7... Comparison circuit, 8... Error amplification circuit, 9... Comparison circuit, 10... AND circuit, 11
... Drive circuit, 12 ... Rectification smoothing circuit, 13
...Detection circuit, 14...Diode, 15...Capacitor, 16-18...Resistor, 21...Input winding, 22...Output winding, 23...Bias winding,
41...Resistor, 42...Diode, 43...Capacitor, 44...NPN transistor, 45...
...Resistor, 46... Zener diode, 47...
PNP transistor cut mirror, 51...resistor,
52... Inverting circuit, 53... Resistor, 48, 49...
...NPN transistor, 54, 55...NPN transistor, 56...PNP transistor, 57~
59...NPN transistor, 61...Resistor, 6
2...NPN transistor, 63...Resistor, 64
... Zener diode, 65 ... NPN transistor, 66 ... Diode, 67 ... Zener diode, 68 ... Resistor, 69 ... Capacitor, 70 ... PNP transistor, 71 ... Specified voltage source, 72 to 74 ... NPN transistor, 7
5, 76...PNP transistor, 77...NPN
Transistor, 78...Resistor, 80...NPN transistor, 81...Photocoupler light receiving transistor, 81'...Photocoupler light emitting diode.

Claims (1)

[Claims] 1 A switching transformer having an input winding, an output winding, and a bias winding, one end of the input winding being connected to the positive electrode of a DC voltage source, and the other end being connected to the DC voltage source through a main switching element. By connecting the main switching element to the negative electrode of the main switching element and switching the main switching element at a time ratio controlled by a control circuit, the flyback voltage induced in the output winding during the off period of the main switching element is rectified. The control circuit is configured to smooth and obtain a stabilized DC output voltage, and to bias the control circuit by rectifying and smoothing the flyback voltage induced in the bias winding during the OFF period of the main switching element. A pulse generating circuit is provided that sends out a first pulse inverted in synchronization with the flyback voltage, and charges the capacitor to a first specified voltage value during the off period.
When the main switching element is turned on, a charging/discharging circuit is provided which discharges the capacitor via at least a resistor to the forward voltage of the bias winding generated at a negative potential, and the voltage of the capacitor and the first
a first comparator circuit that compares a second specified voltage value set lower than a specified voltage value of and becomes "H" when the second specified voltage value is low, and detects the DC output voltage; An error amplification circuit is provided which generates a third specified voltage value corresponding to this, and an error amplifier circuit that compares the voltage of the capacitor and the third specified voltage value and becomes "H" when the third specified voltage value is low. 2 comparison circuits, and an AND circuit that generates a second pulse that is the AND of the first pulse, the output of the first comparison circuit, and the output of the second comparison circuit,
A self-oscillation type switching power supply device comprising a drive circuit that amplifies the second pulse to drive the main switching element.