JPS60194757A - Switching power source - Google Patents

Abstract

PURPOSE:To enhance the frequency and the efficiency by coupling a control circuit and a drive circuit through a capacitor, rectifying and smoothing the winding voltage of a switching output transformer as a power of the control circuit and the drive circuit. CONSTITUTION:A DC voltage produced by rectifying by a rectifier 2 a commercial AC power 1 is applied through a starting resistor 9 to a switching power source controller 12 and a drive transistor 11 at a power source starting time. After starting, a voltage produced by rectifying and smoothing the winding voltage of a switching output transformer 4 is applied to the controller 12 and the transistor 11. The controller 12 and the transistor 11 are connected through a capacitor 15, and a capacitor 32 of a small capacity is connected between the power source voltage line of the controller 12 and an earth.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a switching power supply device used as a power supply circuit for a television receiver or the like.

Structure of a conventional example and its problems FIGS. 1 and 3 show a passive drive circuit of a conventional switching power supply. Figure 1 shows the forward polarity drive system;
The figure shows a reverse polarity drive circuit.

In FIG. 1, 1 is an AC power supply, 2 is a bridge rectifier diode, 3 is a smoothing capacitor, 4 is a switching output transistor, 5 is a switching output transistor, 6 is a resistor and a capacitor for improving the switching characteristics of the switching output transistor, 7 is a drive transformer, 8 is a drive current limiting resistor, 9 is a starting resistor, 1o is a rectifier circuit (consisting of DI, D2.Ll, and CI) that creates the B voltage of the drive circuit and control circuit, 11 is a drive transistor, and 12 is a Control circuit (oscillation circuit,
(composed of a constant voltage circuit, a protection circuit, etc.), 13 is a load resistance of the transistor 12a in the control circuit output stage, 14 is a capacitor that limits the voltage of the drive transformer,
18 is a switching output transformer reset circuit (D5
．． 19 is a DC output voltage rectifier circuit (consisting of C3 and R2).
D3°D4, I2, C2, and R1) are shown respectively.

FIG. 3 shows a circuit diagram of the reverse polarity drive system, and the difference from that in FIG. 1 is the connection method of the drive transformer 7 and the connection method of the drive transistor. The other circuit configurations are the same as those in FIG. 1. The black dots drawn on the switching output transformer 4 and the drive transformer 7 indicate the beginning of winding of the coil.

FIG. 2 shows the on/off relationship of the drive transistor 11 and the output transistor.

It is shown in Figure 4. FIG. 2 shows the on/off relationship of each transistor in the forward polarity drive system shown in FIG. 1. OVa is the output voltage of the control circuit 12, Vc is the collector voltage of the drive transistor 11, and vb is the base voltage of the output transistor transistor. , Ic represents the collector current of the transistor 6. Fluctuations in the output voltage are converted into pulse widths by the control circuit, and the on-period of the output transistor is controlled to stabilize the output voltage. The period from t1 to t2 in FIG. 2 shows the above-mentioned on period. During this period, the transistor 12a.

11 becomes conductive, and a voltage that makes Sl positive is induced in the 31.82 winding of the drive transformer, so that transistor 5 becomes conductive. Between 12 and 13, the transistor 12
Since transistors a and 11 become non-conductive, a voltage that makes Sl negative is induced in the secondary winding of the drive transformer, so transistor 5 also becomes non-conductive.

As described above, the switching power supply shown in FIG. 1 is characterized in that when the drive transistor 11 becomes conductive, the switching output transistor 5 also becomes conductive at the same time.

FIG. 4 shows the relationship between conduction and non-conduction of each transistor in the reverse polarity drive method shown in FIG.

Va, Vc, vb, and Ic are voltage currents measured at the same measurement points as in FIG.
1 becomes non-conductive. At this time, a positive voltage is induced at the 82 terminal of the drive transformer 7 since the connection is reversed to that shown in FIG. 1, and the transistor 6 becomes conductive. During the period T2 to T3, transistor 11 is conductive, and conversely, transistor 6 is non-conductive.

As described above, the switching power supply shown in FIG. 3 is characterized in that the output transistor 5 becomes conductive when the drive transistor 11 becomes non-conductive.

FIGS. 5 and 6 show the AC power supply rectified voltage V1. The relationship between the output voltage Va of the control circuit, the operating current 11 flowing through the control circuit, and the operating current I2 passing through the drive circuit is shown. FIG. 6 shows the characteristics in the forward polarity drive system. When the power switch 2o is turned on at tl, the switching power supply starts operating at t2 due to the start resistor 9. Until t2, the transistor 12a of the control circuit is non-conductive. Therefore, since the transistor 11 is also non-conductive, the operating current 2 of the drive circuit becomes Q. Similarly, when the protection circuit is operating, if the oscillation circuit of the control circuit is stopped, the drive transistor becomes non-conductive and the transistor 2 becomes 0.
becomes.

Next, in Fig. 6, Va in the reverse polarity drive system
Examining the relationship between and 2, when starting and when the protection circuit is operating, the drive transistor 11 is in a conductive state because the transistor 12a is non-conductive, contrary to the case of the forward polarity drive system. Therefore, I2 is flowing even at the start. Ignoring the collector-emitter voltage of the transistor 11 and the resistance between the drive transformers P1 and P2, V 2 =I2R8 (1).

If the minimum operating voltage of the control circuit is v2MIN, then I2 must satisfy the following equation in order for the circuit to start operating.

In order to allow I2 to flow, the start resistor 9 may be made smaller, but the smaller it is, the greater the loss in the start resistor 9 becomes, which is not preferable.

As described above, when using the reverse polarity drive system shown in FIG. 3, it is necessary to reduce the starting resistance, which is a major drawback of the reverse polarity drive system power supply.

In a steady state of operation, the loss of the start resistor 9 cannot be ignored, so the start resistor 9 is often turned off when a switch circuit is installed.

However, when an abnormality occurs and the protection circuit operates, this switch circuit is turned on and the start resistor 9 is often connected. The reason for this is that if you use a switch circuit such as an SCR to ensure that once the switch circuit is activated, it will never turn on, the start resistor 11 will open due to, for example, a momentary power outage or the timing of turning on and off the power switch. If the output voltage disappears, the switch circuit is always turned on and the start resistor is connected.

In this way, the start resistor 11 may remain conductive for a long time in the event of an abnormality, so a small resistance value means that the rated power of the resistor is large, and the shape must also be large.

In order to solve these problems, it is possible to use a forward polarity drive system as shown in Figure 1, but when increasing the switching frequency or increasing the output, a reverse polarity drive is a simpler circuit. This configuration has the advantage of fully bringing out the switching characteristics of the switching output transistor. As described above, solving the above-mentioned problems in the circuit of FIG. 3 can have a great effect on increasing the frequency and output of the switching circuit.

Furthermore, until now, it has been assumed that the transistor 12a of the control circuit is non-conductive when the protection circuit is in operation. In this method, once the protection circuit operates, it does not recover even if the abnormal condition is removed, and is called a shutdown method. This method is often used especially in overvoltage protection circuits. In addition to this type of protection circuit, there is a current-limiting type protection circuit that is often used in overcurrent protection circuits. This is a method that limits the current when an abnormality occurs and returns to normal operation as soon as the abnormality is removed. Since overcurrent occurs when the load is short-circuited, the output voltage of the rectifier circuit block 10 that supplies the B voltage v2 of the control circuit and drive circuit is not generated. will be supplied only. Therefore, the v2 voltage decreases, the drive current of the chemical transistor becomes insufficient, and sufficient switching is not performed, resulting in abnormal heat generation and destruction of the transistor 5.

Purpose of the Invention The present invention is directed to a switching power supply that eliminates such conventional disadvantages, improves the switching characteristics of switching output transistors, achieves higher frequency and higher efficiency, and prevents abnormal heat generation and destruction of the transistors. The purpose is to provide equipment.

Structure of the Invention In the present invention, when the power supply is started, a switching power supply control circuit such as an oscillation circuit and a pulse width control circuit and a reverse polarity drive circuit are activated by a starting resistor connected to a DC power line obtained by rectifying a commercial AC power supply. In the switching power supply circuit, the control circuit and the drive circuit are activated by supplying a power supply voltage of The voltage obtained by rectifying and smoothing the winding voltage of the switching output capacitor is supplied as the power supply voltage for the control circuit and drive circuit through a diode, and a small capacitor is connected between this power supply voltage line and the ground. It is characterized by connecting.

DESCRIPTION OF EMBODIMENTS FIG. 7 shows an embodiment of a switching power supply circuit using the reverse polarity drive system of the present invention. 15 is a coupling capacitor, 16 is a reverse breakdown voltage protection diode between the emitter and base of transistor 11, and diode 21 is a capacitor C of rectifier circuit block 1o at the time of start and protection circuit operation.
The switching diode and capacitor 22 that separate the circuit 1 from the circuit are also decoupling capacitors for the power supply voltage (hereinafter referred to as v2) line of the control circuit and drive circuit, which mainly operate at the time of starting and when the protection circuit operates.

Under normal operating conditions, the capacitor of the v2 line is isometrically the sum of capacitors 22 and 01.

The operating characteristics of this circuit at the time of start and during protection circuit operation will be explained with reference to FIG. When the power switch 2o is turned on at tl, the transistor 12a of the control circuit is non-conductive, so the voltage of Va is equal to the AC power rectified voltage v.
It rises with the same rise time as 1. The rise time of vl is slow, several QmsI3c, and the rise of va is the same as vl, so the load resistance is 13. By selecting the constants of the coupling capacitor 16 and the emitter-base resistor 17 of the transistor 11, it is possible to prevent the transistor 11 from becoming conductive due to the rise characteristics of Va.・Resistance 13, 1.7 2-3
If the capacitor 16 is set to Ω, the capacitance value of the capacitor 16 is 0.
If the voltage is 1 μF or less, the transistor 11 will not conduct.

Since the oscillation circuit of the control circuit operates at t2, V
The voltage a becomes a rectangular wave of tens of KHz or more as shown in FIG. 4, and is applied to the base of the transistor 11 by the coupling capacitor 11, so that the circuit operates normally. The value of the capacitance of the capacitor 16 is actually selected to be about 0.01 μF since it is sufficient to pass this pulse of several tens of KHz.

If the overvoltage protection circuit operates at t3, the oscillation circuit of the control circuit stops and the transistor 12a becomes non-conductive. Therefore, the direct current is cut off by the capacitor 15, and the transistor 11 becomes non-conductive. In this way, at the time of starting and when the overvoltage protection circuit is operating, the drive transistor 11 becomes non-conductive, so the drive current factor 2 becomes 0. Therefore, the resistance value of the start resistor 9 is made larger than the start resistance value in the circuit shown in FIG. can. This has a great effect in reducing the loss and size of the start resistor 9.

Furthermore, by adding the diode 21 and the capacitor 22 at the same time as the coupling capacitor 16, it is possible to prevent abnormal heat generation or destruction of the output transistor transistor when the load is shorted.

FIG. 9 shows an equivalent circuit of the start circuit when the load is short-circuited with and without the diode 21 and capacitor 22. FIG. 9a shows the case where it does not exist, and FIG. 10 shows the case where it does. 23 shows a combination of a control circuit and a drive circuit. When the voltage on the v2 line becomes lower than the operation stop voltage of the control circuit, the circuit stops operating, and the output transistor becomes non-conductive. When the circuit operation stops, the drive current stops flowing, so the v2 voltage increases. Further, when the v2 voltage becomes equal to or higher than the operation start voltage, the circuit operates and a drive current flows.

This current causes the voltage to drop again and the operation stops.

In this way, the circuit operates intermittently. The intermittent operation time at this time varies depending on the capacitance value of C1. By shortening this intermittent operation time as much as possible and conversely increasing the time during which the circuit is inactive, it is possible to reduce the heat generated by the output transistor 5 when the load is short-circuited. In order to shorten the operating time, the capacitance value of C1 must be reduced, but the value of capacitor C1 is a rectifying and smoothing capacitor, which prevents ripple current from flowing and stabilizes the power supply voltage line of the control circuit and drive circuit. It cannot be reduced in meaning.

Therefore, the diode 21. of this circuit. The effect of adding the capacitor 22 will be described below.

In FIG. 9, when the load is short-circuited, the rectified voltage of the rectifier block 10 becomes low and the diode 21 becomes non-conductive. Therefore v
Since there is only 22 capacitors for the 2 lines, the capacitance value of this capacitor 22 can be freely selected unlike in the case of FIG. 7a. As mentioned above, this capacitor 22
By reducing the capacitance value of , the amount of charge accumulated in the capacitor 22 by the start resistor 9 during the circuit down time is reduced. This charge is discharged when the voltage of the v2 line exceeds the operation start voltage of the control circuit and the circuit starts operating. This discharge time becomes the operating time of the circuit, and if the amount of charge in the capacitor 22 is small, the time required for the circuit to drop to the operating stop voltage is shortened, and the operating time is shortened. Therefore, by adding the diode 21, the capacitance value of the capacitor 22 can be reduced, and the intermittent operation time can be shortened, so that the output transistor generates less heat.

Effects of the Invention As described above, according to the present invention, in a switching power supply device that has a starting circuit using a start resistor and further has a reverse polarity drive circuit, the operating characteristics at the time of starting and at abnormal times can be improved. The effect of increasing the frequency and increasing the output using a simple drive circuit is great.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional switching power supply circuit using a forward polarity drive system, Figure 2 is an operating waveform diagram in the above circuit, and Figure 3 is a circuit diagram of a conventional switching power supply circuit using a reverse polarity drive system. Figure 4 is an operating waveform diagram of the above circuit, Figure 5 is its operating characteristic diagram during forward polarity drive, and Figure 6 is a diagram of its operating characteristics during forward polarity drive.
FIG. 7 is a diagram of operating characteristics during reverse polarity drive, and FIG. 7 is a circuit diagram of a switching power supply device according to an embodiment of the present invention.
FIG. 8 is an operational characteristic diagram of the above circuit, and FIG. 9a is a diagram. b is an equivalent circuit diagram of the load/iodine start circuit. 4...Switching output lance, 5...
・Switching output transistor, 6... Resistor and capacitor, 7... Drive transformer,
9... Start resistor, 1o... Rectifier circuit, 11... Drive transistor, 12...
Old...Control circuit, 13...Load resistance,
14.15... Capacitor, 18... Reset circuit, 19... Output voltage rectifier circuit, 16...
... Diode, 21 ... Switching diode, 22 ... Capacitor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4 Figure 5 Figure 7

Claims (1)

[Claims] When starting the power supply, the starting resistor connected to the DC power line obtained by rectifying the commercial AC power supply supplies the power supply voltage for the switching power supply control circuits such as the oscillation circuit and pulse width control circuit, and the reverse polarity drive circuit. After startup, a switching power supply circuit is provided that operates the control circuit and drive circuit using the voltage obtained by rectifying and smoothing the winding voltage of the switching output transformer.The control circuit and drive circuit are coupled by a capacitor, and the switching The voltage obtained by rectifying and smoothing the winding voltage of the output transformer is supplied as the power supply voltage for the control circuit and drive circuit through a diode, and a small capacitor is connected between this power supply voltage line and the ground. switching power supply.