JPS63299778A - Self-oscillation type switching power source device - Google Patents

Abstract

PURPOSE:To operate stably, by a method wherein a capacitor is charged (discharged)synchronizing with the putting ON of a main switching element when the same element is put ON once and the OFF condition of the main switching element is kept forcibly until both terminal voltage arrives at a speci fied voltage. CONSTITUTION:A self-oscillation type switching power source device is constitut ed of a rectifying and smoothing circuit 1, a switching transformer 2, a main switching element 3, a starting resistor 4, a control circuit 5, a drive circuit 6, the detecting circuit 11 of a DC output voltage and a photocoupler 12 for feedback and outputs the stabilized DC output voltage. Further, the same power source device is provided with resistors 13-16, NPN transistors 17-19, a speci fied voltage source 30, a capacitor 31, a Zener diode 32, a comparator 33 and a constant current source 34. According to this constitution, the minimum value of the period of time of OFF of said power source device, whose periods of time of ON, OFF become short, may be regulated when a DC output current becomes small, whereby the title device may be operated stably.

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.

2. Description of the Related Art A conventional self-oscillation type switching power supply device has a configuration as shown in FIG. In FIG. 3, 1 is a rectifier and smoothing circuit which converts the received AC input voltage into DC input voltage. 2 is a switching transformer with a primary winding 21. It has bias windings 22, 2 and a secondary winding 23. 3 is a main switching element which turns on and off to convert the DC input voltage into a high frequency AC voltage and input it to the primary winding 21. 4 is a starting resistor, 6 is a control circuit, 6 is a Tom Eve circuit, 7 is a diode, and 8 is a capacitor. The high frequency AC voltage generated in the bias winding 22 is rectified and smoothed by the diode 7 and capacitor 8, and the control circuit 6 is biased. Supply voltage. A diode 9 and a capacitor 10 rectify and smooth the high frequency AC voltage generated in the secondary winding 23, and supply a DC output voltage. 11 is a detection circuit that detects a DC output voltage; 12 is a photocoupler that feeds back information about the DC output voltage detected by the detection circuit 11 to the control circuit 5; The operation of the conventional example will be explained below.

The AC input voltage input to the rectifying and smoothing circuit 1 is converted to a DC input voltage, and biases the control circuit 5 via the starting resistor 4. The biased control circuit 5 outputs a pulse,
The signal is amplified by the drive circuit and turns the main switching element 3 on and off.

Then, the DC input voltage is converted to a high frequency AC voltage and input to the primary winding 21, and high frequency AC voltages are generated in the bias winding 22 and the secondary winding 23 according to their respective turns ratios. The high frequency AC voltage generated in the bias winding 22 is rectified and smoothed by the diode 7 and the capacitor 8, and is supplied to the control circuit 5 as a bias voltage. The high frequency AC voltage generated in the secondary winding 23 is passed through a diode 9 and a capacitor 1.
0, the flyback is rectified and smoothed and supplied as a DC output voltage. The DC output voltage is fed back to the control circuit 6 by the detection circuit 11 via the photocoupler 12. The control circuit 6 detects the high frequency alternating current voltage generated in the bias winding 22, and the period during which the flyback voltage disappears, that is, the main switching element 3 is on (hereinafter referred to as the on period), is the period during which the main switching element 3 is off. When the excitation energy stored in the switching transformer 2 is exhausted during the off period), the output is set to H,
The main switching element 3 is turned on via the drive circuit 6. Then, after receiving the information from the 7 Otocoupler 12,
In order to stabilize the DC side voltage, the on-period is determined, the first output leading to the on-period is set to L, and the main switching element 3
Turn off. The above operation supplies a stable DC forward voltage. The number of turns of the primary winding 21 is N1.Secondary winding 2
The winding No. 3 is Ns, and the on period is T. H, off period T. 2
2. The DC input voltage is vi, and the DC output voltage is V. ,JA,
If the forward voltage drop of the diode 9 is ignored, the following equation holds true.

On the other hand, the DC output current is set to 61:00. UT is expressed as "ON + TOFF (synchronization)" where the primary winding inductance is .

FIG. 4 shows a waveform diagram of the drain-to-north voltage vDs of the main switching element 3, the current flowing through the primary winding 21, and the current flowing through the secondary winding 23 in a conventional circuit.

Problems to be Solved by the Invention In such a conventional configuration, as can be seen from equations 1 and 2 above, a DC voltage source is required. . , decreases, T proportionally. N and T. 7. is decreasing.

However, depending on the capabilities of the main switching element 3, drive circuit 6, or control circuit 6, T. H has a minimum value T
. , l exists, and ToN is T. If an attempt is made to reduce the value to less than N, intermittent oscillation may occur or the main switching element 3 may perform class A operation. When intermittent oscillation occurs, the response to a transient phenomenon such as a sudden change in the DC output current deteriorates, and when class A operation occurs, the main switching element 3 generates heat.

The present invention solves these problems, and even when using the same main switching element, drive circuit, and control circuit capabilities as the conventional configuration, and a switching transformer with the same specifications, it is possible to stably reduce the DC output current to a lower level. The present invention provides a self-excited oscillation type switching power supply device having operating means.

A foolproof way to solve problems In order to solve this problem, the present invention has the following features.

The high-frequency AC voltage generated in the bias winding of the chimbu transformer is detected, and a pulse is generated in synchronization with the excitation energy of the switching transformer being released and the flyback voltage disappearing. In addition to a control circuit that controls and outputs stably, and a drive circuit that inputs the pulse via a resistor to drive the main switching element, amplifies it, and outputs it, the input pulse of the drive circuit is A charging/discharging circuit that charges and discharges a capacitor synchronously, a comparison circuit that compares the voltage across the capacitor with a specified voltage value, and an output of the comparison circuit that is driven through a resistor to turn the input of the drive circuit on and off. and a second transistor that is driven by the input pulse of the drive circuit and turns on and off between the base and emitter of the first transistor, and when the main switching element turns off by -H, at least The device is configured to forcibly remain off for a specified period of time.

With this configuration, when the main switching element turns off at -H, the capacitor is charged (or ID discharged) at L,
The capacitor remains off for at least the time required for the voltage across the capacitor to reach a specified voltage. Then, even if the DC output current decreases and the on period and off period become shorter, the minimum value of the off period is regulated, so the on period is not shorter than when the off period is not restricted, and less DC output is generated. Stable operation is achieved up to the current level. The minimum value of the on period is T. , and T is the period during which the flyback voltage is generated, that is, the period during which the excitation energy of the switching transformer finishes discharging, with respect to TOH. 2. ′, the minimum output current that can be stably obtained with the conventional configuration is expressed as the equation (1) above. tI? is obtained from equation (2) above. On the other hand, if the means of the present invention is provided and the regulated minimum off period is Toyy, then from equations (5) and (6), according to the present invention, (To8HIN+Toyy') / (To
:” + To, :”) can make MXN smaller. To, MIN to T. , MIゞ＞”OF
It is obvious to set it to F'.

Embodiment FIG. 1 is a circuit diagram of a self-excited oscillation type switching power supply device according to an embodiment of the present invention. 1 to 1 in Figure 1
2 is equivalent to that shown in the conventional example. 13 to 16 are resistors, 17 to 19 are NPN transistors, 3o is a specified voltage source, whose voltage is Vl, (. 31 is a capacitor, and the voltage across it is V. 32 is a Zener diode; The Zener voltage is assumed to be v2. 33 is a comparator, and VC is inputted to the O input terminal, and V□ is inputted to the ■ input terminal. 34 is a constant current source, and its current value is expressed as . The operation will be explained below. explain.

The AC input voltage input to the rectifying and smoothing circuit 1 is converted into a DC input voltage V□, which biases the control circuit 6 via the starting resistor 4. Then, the control circuit 6 outputs a pulse, which is input to the drive circuit 6 via the resistor 13, where it is amplified and output so that the main switching element 3 can be turned on and off. The main switching element 3 causes the DC input voltage v
4 is converted into a high frequency AC voltage and input to the primary winding 21, and high frequency AC voltages are generated in the bias winding 22 and the secondary winding 23 according to their respective turns ratios. The high frequency AC voltage generated in the bias winding 22 is rectified and smoothed by the diode 7 and the capacitor 8, and is supplied to the control circuit 6 as a bias voltage. The flyback voltage of the high frequency AC voltage generated in the secondary winding 23 is rectified and smoothed by the diode 9 and the capacitor 1o, resulting in a DC output voltage V. U
Supplied as T. DC output voltage V. +JT is fed back by the detection circuit 11 to the control circuit 6 via the photocoupler 12. The control circuit 6 has a bias winding 22
The high frequency alternating current voltage generated is detected, and the flyback voltage disappears. That is, when the excitation energy stored in the switching transformer 2 during the on period is exhausted, the output is set to H and the main switching element 3 is turned on via the resistor 13 and the drive circuit 6. Then, upon receiving information from the photocoupler 12, the DC output voltage V is determined. U? In order to stabilize the on-period, an on-period is determined, and when the on-period is reached, the output is set to L and the main switching element 3 is turned off.

The above operation supplies a stable DC output voltage vOUT. On the other hand, during the on period, a base current flows through the transistor 19 through the resistor 16, turning on the transistor 19 and shorting both ends of the capacitor 31 and the Zener diode 32. Then, the output of the comparator 33 is H, but since the transistor 18 is turned on by being supplied with the base current through the resistor 16, the transistor 17 is turned off, and in the end, the input voltage v1 of the drive circuit 6 becomes H during the on period. It will remain as . Next, when the output v2 of the control circuit 6 becomes L, the main switching element 3 is turned off, and at the same time, the base current supply to the transistors 18 and 19 is cut off, and the transistors 18 and 19 are turned off. Then, the capacitor 31 is charged by the constant current source 34, and the comparator 331d H outputs until the voltage V across the capacitor 310 reaches the voltage vTH of the specified voltage source 3°, and the transistor 1T outputs the base current through the resistor 14. Supplied and turned on. capacitor 3
As charging of 1 progresses and vo>vTH, comparator 3
Since the output of transistor 3 is inverted and becomes L, the base current supply to transistor 17 is cut off and the transistor 17 is turned off. That is, the capacitor 31 is 0. During the charging period from VTHKt to VTHKt, vl is forcibly set to L by the transistor 17, and even if the flyback voltage disappears within this period and the output v2 of the control circuit 5 becomes H, the output v2 from the drive circuit 6
The main switching element 3 remains off, and when the charging period of the capacitor 31 ends, the transistor 1
After 7 is turned off, vl becomes H and the main switching element 3 is turned on. Further, if v2 remains L when the transistor 17 is turned off, the off period continues, and v2 becomes H and shifts to the on period. in this case,
As the capacitor 31 is further charged, it is eventually clamped to the Zener voltage v2, and the current flows to the Zener diode 32. Capacitor 3 until vc becomes V□
1 charging period or regulatory minimum off period 70. :IN is expressed as follows, assuming that the capacitance of the capacitor 31 is C51.

Figure 2 shows the main switching element 3 through the above operation.
Drain-source voltage vDS, drain current. ,2
Current flowing to the next winding 23! 3. Voltage V across the capacitor 310. , a waveform diagram of the output v2 of the control circuit 5 and the input v1 of the drive circuit 6.

Effects of the Invention As described above, according to the present invention, when the DC output current becomes smaller, the on-period and off-period become shorter. With the main switching element, control circuit, and drive circuit that have the same capabilities as conventional devices, stable operation is possible with less DC output current than conventional devices, which has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing a self-excited oscillation type switching power supply device according to an embodiment of the present invention, FIG. 2 is a waveform diagram of its main parts, and FIG. 3 is a circuit configuration diagram of a conventional self-excited oscillation type switching power supply device. 4 are waveform diagrams of the main parts thereof. 1... Rectifier smoothing circuit, 2... Switching transformer, 3... Main switching element, 4...
...Starting resistor, 6...Control circuit, 6...
...Drive circuit, 7...Diode, 8.
...Capacitor, 9 ...Diode, 1
o...Capacitor, 11...Detection circuit, 12...Photocoupler, 13-15...
...Resistance, 17-18...NPN) Transistor, 30...Specified voltage source, 31゛゛°°°Capacitor, 32...Zener diode, 33...
...Comparator, 16-3-resistance, 19...
...NPN) transistor, 34...constant current source. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure-f (H7-1 Liver Diagram 3

Claims (1)

[Claims] The input DC voltage is converted into a high-frequency AC voltage by a main switching element, inputted to the primary winding of a switching transformer equipped with a primary winding, a secondary winding, and a bias winding, and outputted from the secondary winding. The high-frequency AC voltage generated in the bias winding is rectified and smoothed to supply a specified output DC voltage to the load, and the high-frequency AC voltage generated in the bias winding is detected to detect the flyback voltage generated during the off period of the main switching element. A control circuit has a function of generating a pulse voltage in synchronization with a decrease in the output DC voltage, controlling the pulse width to stabilize the output DC voltage, and outputting the pulse voltage. In addition to the drive circuit that amplifies and outputs the input through the drive circuit, there is also a charging and discharging circuit that charges and discharges the capacitor in synchronization with the input pulse voltage of the drive circuit, and compares the voltage across the capacitor with a specified voltage value. a first transistor that is driven by the output of the comparison circuit via a resistor to turn on and off the input of the drive circuit; and a base transistor of the first transistor that receives the input pulse of the drive circuit. and a second transistor that turns on and off between the emitters, and the self-oscillation switching power supply device is configured to operate such that once the main switching element is turned off, it remains off forcibly for at least a specified time. .