JPH0624435B2 - Switching power supply - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to switching power supplies.

Since the switching power supply is small and highly reliable, and the input and output are insulated by a transformer, etc., it has the advantage that the grounding polarity on the output side can be freely selected. Widely used as a DC power source for. Various circuit systems are known as a switching power supply circuit system, but the present invention relates to a switching power supply system belonging to a semi-self-excited circuit system.

Prior Art FIG. 1 shows a conventional example of a semi-excited switching power supply.
Reference numerals 2 and 3 are AC input terminals, 3 is a power switch, 4 is an input rectifier circuit including a rectifier circuit such as a diode bridge rectifier circuit and a filter circuit, and 5 is a smoothing capacitor. The AC input supplied to the input terminals 1 and 2 is rectified by the input rectifier circuit 4, smoothed by the smoothing capacitor 5, and converted into a DC voltage Vin.

Reference numeral 6 is a transformer, 61 to 63 are windings of the transformer 6, and 7 is a switching element constituted by a power transistor or the like, which is connected in series to the winding 61 of the transformer 6.
Reference numeral 8 is a starting circuit, 9 is a control circuit, 10 is an output rectifying / smoothing circuit, and 11 and 12 are output terminals.

The starting circuit 8 has a series connection circuit of a resistor 81 and a zener diode 82 connected in parallel to a DC input line, and a connection point of the resistor 81 and the zener diode 82 is connected to the base of a transistor 83. The transistor 83 has a collector connected to the (+) side line (a) of the DC input through the resistor 84, and an emitter connected to the power supply line of the control circuit 9. Reference numeral 85 is a capacitor.

The control circuit 9 causes the voltage detector 91 to detect the DC output voltage Vo.
Is detected, and the detection signal is transmitted to the control unit 94 through a photo coupler such as the photodiode 92 and the photo transistor 93, and the control unit 94 drives and controls the switching element 7. The control unit 94
At the time of start-up, the start-up circuit 8 starts up with the voltage applied thereto, and after the start-up, the winding 63 operates with the voltage applied through the diode 13.

The output rectifying / smoothing circuit 10 includes diodes 101 and 102, an inductor 103, and a capacitor 104.

In the above conventional semi-self-excited switching power supply, first, the power switch 3 is turned on to turn on the AC100V or 200
When the AC power source of V is turned on, the DC voltage Vin appearing between the terminals of the smoothing capacitor 5 rises with time, and the voltage applied to the Zener diode 82 exceeds the Zener voltage in a certain time after the power source is turned on. Become. As a result, when the Zener diode 82 becomes conductive, the transistor 83 is turned on, current is supplied to the control circuit 9 through the transistor 83, and the control circuit 9 starts operating.
When the operation of the control circuit 9 is started, the switching element 7 is started to start the switching operation, and the voltage is induced in the winding 63. The voltage induced in the winding 63 is the diode 13
Is supplied to the control circuit 9 through the control circuit 9, the control circuit 9 enters a steady operation by using the voltage induced in the winding 63 as an operating power source.

However, in this conventional example, since it is necessary to make a power supply for the control circuit of several V from the DC input voltage Vin of about 130 V or 260 V in this conventional example, in the circuit components such as the resistors 81 and 84 and the Zener diode 82. The power loss becomes large, the efficiency at the time of starting becomes poor, and the transistor 8
3 has a high withstand voltage, a transistor for a small signal cannot be used, and it is difficult to reduce the size and cost.

The object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide a starting circuit constituted by using components that are small in capacity, low in power consumption, high in efficiency and capable of forming a hybrid IC. Another object of the present invention is to provide a semi-self-excited switching power supply that can achieve miniaturization of circuit configuration and high efficiency.

To achieve the above object, the present invention provides a transformer, a switching element that switches a direct current supplied through the transformer, a control circuit that drives and controls the switching element, and the control circuit when the power is turned on. A switching power supply comprising: a starter circuit that supplies starter power to the transformer; and a winding that is provided in the transformer and that supplies operating power to the control circuit after the control circuit is started by the starter circuit, The start-up circuit is connected between the DC input lines, and conducts when the DC input exceeds a certain level to be charged in one direction, and a charging voltage in the time constant circuit has a certain level. A first switching circuit that conducts when the above is reached, and a conduction by the conduction of the first switching circuit, and the time constant circuit for the control circuit. A second switching circuit which supplies the charging voltage of the second switching circuit to activate the first charging circuit, drives the first switching circuit, and is self-held through the first switching circuit. The switching circuit and the control circuit are connected so that the operating power generated in the winding is supplied to the control circuit through the second switching circuit.

Embodiment FIG. 2 is an electric circuit connection diagram of a switching power supply according to the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same components. In the figure, 86 is a time constant circuit, 87 is a first switching circuit, and 88 is a second switching circuit.
Of the switching circuit, and these constitute the starting circuit 8.

The time constant circuit 86 includes a resistor 861 and a Zener diode 86 between the DC input lines (a) and (b) to which the DC voltage Vin, which is the terminal voltage of the smoothing capacitor 5, is supplied.
2 and a capacitor 863 are connected in series to form a circuit configuration. After closing the power switch 3 and turning on the power, the DC input voltage Vin, which is the terminal voltage of the smoothing capacitor 5,
Is above a certain level and the voltage applied to the Zener diode 862 is above that Zener voltage, the Zener diode 862 becomes conductive and the capacitor 863 passes through the Zener diode 862 and the resistance value R1 of the resistor 861 and the capacitor 863 It is charged in one direction according to the time constant determined by the capacitance value C1.

The first switching circuit 87 includes a series circuit of a resistor 871 and a Zener diode 872, and the time constant circuit 86
Is connected to one end of the capacitor 863 and the other end is connected to the base of the transistor 873. The transistor 873 has a resistor 8 between its base and emitter.
74 and the collector is connected to one end of a capacitor 863 through resistors 876 and 877. This first
In the switching circuit 87, the time constant circuit 86
When the charging voltage of the capacitor 863 configuring the above becomes higher than a certain level, the Zener diode 872 becomes conductive, and then the transistor 873 becomes conductive.

The second switching circuit 88 is the PNP transistor 8
81 is provided. The transistor 881
Connects its base to the connection point of the resistor 876 connected to the collector of the transistor 873 and the resistor 877, and connects the emitter together with the resistor 877 to one end of the capacitor 863 of the time constant circuit 86. At the same time, the collector is connected to the control circuit 9, and is further connected to the base of the transistor 873 forming the first switching circuit 87 through the series circuit of the resistor 882 and the Zener diode 883. The Zener diode 883
The zener voltage of is set to be lower than that of the zener diode 872. The emitter of the transistor 881 is connected to one end of the diode 13 connected in series with the winding 63.

In the above circuit configuration, when the power switch 3 is closed and the power is turned on, the DC voltage Vin, which is the voltage across the terminals of the smoothing capacitor 5, rises with time. Smoothing capacitor 5
DC voltage Vin, which is the terminal voltage of, exceeds a certain level,
When the voltage applied to the Zener diode 862 becomes equal to or higher than the Zener voltage, the Zener diode 862 becomes conductive and the capacitor 863 causes the Zener diode 862 to
Through, the resistance value R1 of the resistor 861 and the capacitor 86
Time constant R1. It is charged in one direction according to C1.

The charging voltage of the capacitor 863 is applied to the first switching circuit 87. Then, when the charging voltage of the capacitor 863 reaches a certain level or higher, the Zener diode 872 first conducts, the base drive is applied to the transistor 873, and the transistor 873 turns on.

When the transistor 873 is turned on and the collector current flows in this manner, the transistor 881 forming the second switching circuit 88 is driven and turned on. When the transistor 881 is turned on, the charging voltage of the capacitor 863 is applied to the control circuit 9, and the control circuit 9 starts its operation by the charged electric charge. At the same time, the resistance 88
2 and the Zener diode 883 from the collector side of the transistor 881 to the transistor 873,
It takes a base drive. Therefore, the transistor 881 included in the second switching circuit 88 is self-held through the transistor 873 included in the first switching circuit 87.

When the operation of the control circuit 9 starts, the switching element 7 is activated and the DC voltage Vin applied through the winding 61 of the transformer 6 is switched. Along with this switching operation, the voltage induced in the winding 63 is supplied to the control circuit 9 through the diode 13 and the transistor 881, and thereafter the control circuit 9 continues to operate by using the induced voltage generated in the winding 63 as a power source, and the steady operation is performed. to go into.

When the input voltage decreases and the induced voltage in the winding 63 decreases, and the voltage applied to the Zener diode 883 becomes equal to or lower than the Zener voltage, the self-holding operation of the transistors 873 and 881 is released, and the current flowing in the control circuit 9 is released. Is cut off and the switching operation is stopped.

As described above, the starting circuit 8 according to the present invention utilizes the charging voltage of the capacitor 863 of the time constant circuit 86 to make the first switching circuit 87 and the second switching circuit 88.
Of the capacitor 863 at the time of startup because the circuit configuration is such that the startup power is supplied to the control circuit 9 by sequentially driving
It suffices to pass the charging current for Therefore, as the resistor 871 and the Zener diode 872, it is possible to use those having a remarkably small capacity as compared with the conventional one, the circuit configuration is downsized, and the power consumption is reduced. Transistors (873, 881), resistors (874, 876,
877) and other circuit components such as the Zener diode 883.

Moreover, as shown in the embodiment, the first and second switching circuits 87 and 88 are transistors (873 and 88).
1), resistors (871, 874, 876, 877) and Zener diodes (872, 883), etc., so that a hybrid IC can be realized and the size can be further reduced.

Further, for example, when the input voltage drops or when the induced voltage of the winding 63 drops below a predetermined level due to other abnormality, the self-holding operation of the first switching circuit 87 and the second switching circuit 88 is canceled, Since the drive is prohibited, there is an advantage that operation safety can be secured.

Advantageous Effects of the Invention As described above, the present invention includes a transformer, a switching element that switches a direct current supplied through the transformer, and a control circuit that drives and controls the switching element.
A starting circuit that supplies starting power to the control circuit when the power is turned on, and a winding that is provided in the transformer and that supplies operating power to the control circuit after starting the control circuit by the starting circuit. And a time constant circuit connected to the DC input line between the DC input lines, the time constant circuit being conductive and being charged in one direction when the DC input exceeds a certain level, and the time constant circuit. A first switching circuit that is turned on when the charging voltage at a certain level is higher than a certain level, and is turned on by the conduction of the first switching circuit, and supplies the charging voltage of the time constant circuit to the control circuit. And a second switching circuit that drives the first switching circuit and that is self-held through the first switching circuit, The winding, the second switch circuit, and the control circuit are connected so that the operating power generated in the winding is supplied to the control circuit through the second switching circuit. Therefore, it has a small-capacity, low-power-consumption, high-efficiency and start-up circuit that is configured by using components that can be used as a hybrid IC. A semi-excited switching power supply can be provided.

[Brief description of drawings]

FIG. 1 is an electric circuit connection diagram of a conventional switching power supply, and FIG. 2 is an electric circuit connection diagram of a switching power supply according to the present invention. 5 ... Smoothing capacitor, 6 ... Transformer 7 ... Switching element, 8 ... Starting circuit 9 ... Control circuit 61, 62, 63 ... Transformer winding 86 ... Time constant circuit 87 ... First Switching circuit 88 ...... second switching circuit

Claims (1)

[Claims] 1. A transformer, a switching element for switching direct current supplied through the transformer, a control circuit for driving and controlling the switching element, and a starting circuit for supplying starting power to the control circuit when the power is turned on. A switching power supply comprising: a winding that supplies an operating power to the control circuit after the control circuit is started by the starting circuit and is provided in the transformer, the starter circuit is provided between the DC input lines. A time constant circuit that is connected and is charged in one direction when the DC input is above a certain level, and a first switching circuit that is conductive when the charging voltage in the time constant circuit is above a certain level. And conducting by the conduction of the first switching circuit, supplying the charging voltage of the time constant circuit to the control circuit to activate it. And a second switching circuit that drives the first switching circuit and is self-held through the first switching circuit, wherein the winding, the second switching circuit, and the control circuit are the windings. A switching power supply, wherein the operating power supply generated in a line is connected so as to be supplied to the control circuit through the second switching circuit.