JPH0260464A - Starting circuit of switching power supply - Google Patents

Abstract

PURPOSE:To reduce the power consumption of an apparatus and to miniaturize a power switching transformer by conducting a signal supply to a controlling circuit by means of a decided signal. CONSTITUTION:A switching power supply starting circuit has a voltage controlling circuit 13, a main switch 16, a power switching transformer 15, a secondary side rectifier circuit 17 and a smoothing filter 18, and said transformer 15 is provided with a third winding 15a to form a power supply for said controlling circuit 13. Further, a reference voltage detection circuit B forming a dropper power supply is composed of a bias resistance 5 connected with the anode side of Zener diode 4, a bias resistance 7 connected in parallel with divisional resistances 2-3, and a detection transistor(Tr) 6 and ON-OFF Tr 11. Thus, when the voltage of a filter capacitor 12 reaches the IC low-voltage detection point for said controlling circuit 13 by closing of an input power supply 1, the subject apparatus can be operated, but its operation is stopped by the Tr 11 till the time when the voltage of said Zener diode 4 is decided.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a switching power supply, and in particular, to a switching power supply start-up with improved operation protection for the input voltage range of the input power supply and system reset operation of the output side load circuit. Regarding circuits.

[Prior Art] As shown in FIG. 3, a conventional switching power supply directly steps down the input voltage using a constant voltage element such as a Zener diode 4 and supplies it to a control circuit 13, and then outputs the voltage to an internal voltage detection circuit of the control circuit 13. It was running. However, in this method, all the current consumed by the control circuit 13 is supplied from the dividing resistor 2, so the power consumption of the dividing resistor 2 is large. It is necessary to absorb the current change of 2 in the Zener diode 4, and the Zener diode 4 requires a large amount of power, which causes problems such as heat generation, a decrease in efficiency, and an increase in the size of the components.

Therefore, in order to improve the power consumption of the example shown in FIG. 3, a system as shown in FIG. 4, which self-generates the control circuit power supply, has been developed. In the example shown in FIG. 4, a voltage conversion transformer 15 is provided with a third winding 15a, and a rectifier diode 14 and a filter capacitor 12 form a power source for a control circuit 13. By setting the voltage of the Zener diode 4 lower than the third winding voltage, the power of the current amplification transistor 9 and feeder resistor 8 can be reduced to zero during normal operation, resulting in a significant power reduction. This circuit is commonly used (The BPC1094 flj control IC was developed for this circuit, suppressing the current up to startup to about IIIA, and reducing the feeder resistor 8 and current when power is applied. This has the effect of reducing the surge current of the amplification transistor 9.)

This method has the effect of reducing power consumption during normal operation, but since the power supply for the control circuit 13 is generated by yourself, when the input voltage is momentarily interrupted as between times t4 and t5 in Figure 5, The operation continues until the voltage of the filter capacitor 12 becomes equal to or lower than VT2 (low voltage detection point of the control IC forming the control circuit 13). The input voltage at this time is significantly lower than during normal operation, and of course the output voltage also decreases to some extent, but the DC/DC converter section A also operates at the maximum pulse width.

Therefore, in order to prevent the main switch 16 from being destroyed due to the saturation of the voltage conversion transformer 15 at this point, each element needs to have sufficient margin. Therefore, voltage conversion transformer 1
5 becomes difficult to design and becomes larger. Also, when the input voltage recovers, the DC/DC converter section A starts up again, so
The output voltage will recover from an intermediate voltage, and there is a risk that the load-side logic circuit will malfunction and the system will run out of control.

[Problems to be Solved] In other words, the above-mentioned switching power supply has disadvantages in that the power consumption during normal operation is very high in the example shown in Fig. 3, and large parts are required; The drawbacks were that the lance was large and there was a risk that the load side would malfunction in the event of a momentary input interruption, causing the system to run out of control.

The present invention has been made in view of the above-mentioned problems, and by supplying signals to the control circuit with deterministic signals, it reduces power consumption, downsizes the power exchange transformer, and prevents system malfunctions during instantaneous power outages. The purpose of this invention is to provide a starting circuit for a switching power supply.

[Means for Solving the Problems] In order to achieve the object L, a switching power supply starting circuit of the present invention includes a voltage control circuit, a main switch, a power exchange transformer, a secondary side rectifier circuit, and a smoothing filter, and the power exchange transformer In a switching power supply circuit, a switching power supply circuit is provided with a third winding to form a power supply for the control circuit, and the voltage is set to be lower than the voltage of the third winding, and the voltage is supplied to the control circuit from the input power supply via a diode. A dropper power supply is provided, a reference voltage of the dropper power supply is supplied from an input power supply dividing resistor, and the control circuit is activated by a signal determining the reference voltage.

[Example] Next, an example of the present invention will be described with reference to the drawings.

In addition, in the following, common reference numerals are given to parts common to the conventional art, and redundant explanations will be omitted.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which numerals 2 and 3 are input voltage dividing resistors, and B is a reference voltage detection circuit.

The reference voltage detection circuit B forming the dropper power supply includes a bias resistor 5 connected to the anode side of the Zener diode 4, a bias resistor 7 connected in parallel with the dividing resistor 2.3, and a detection transistor 6 and an on/off transistor 11 that are directly connected. It consists of.

Now, in Figure 2, is the input type at time t1? When lA1 is turned on, the voltage across Zener diode 4 and filter capacitor 12 becomes 1. A. When the voltage of the filter capacitor 12 reaches the low voltage detection point VT2 of the IC constituting the control circuit 13, the control circuit 13 becomes operational, but the output of the on-off transistor 11 remains unchanged until time t2 when the voltage of the Zener diode 4 is determined The operation has stopped due to this. At time t2, when the voltage of the Zener diode 4 is determined, a start signal is sent from the on-off transistor 11, the control circuit 13 is operated, the DC/DC converter section A is started, and the voltage of the filter capacitor 12 is changed to the voltage conversion transformer 15. The voltage increases to a voltage determined by the third winding 15a (greater than the voltage of the Zener diode 4), and the feeder resistor 8 and current amplification transistor 9 are canted off.

On/Off I/Resistor 1] The input voltage at startup is determined by the F formula.

However, in the above formula R2R3: Resistance value of resistors 2 and 3 ■4: Zener voltage of Zener diode 4 VBE6: Input side voltage of detection transistor 6 It is.

1 The starting input voltage V in equation (1) is set to a voltage that allows this circuit to control the output voltage.

Next, if a momentary interruption occurs in the input at time t4, the output voltage will not show any abnormal fluctuations if the input voltage Vl recovers within -2 or more than the starting input voltage VTI, but if it falls below the starting input voltage v1 Immediately, the on/off transistor 11 operates to stop the operation of the converter section A. For this reason, D C/D
The design input range of C converter section A is starting input voltage VT
It can be limited to I.

Now, if the input voltage V11 recovers and exceeds the starting input voltage VTI again at time t5, the converter section will start immediately,
The output voltage rises again.

In this way, the output voltage v1 of this circuit stops and then rises, so it does not generate an intermediate level output voltage that would cause the load side logic circuit to malfunction, and also Since the system can be reset at the rise of the output voltage, it is possible to prevent accidents where the system goes out of control.
It can be kept small by cutting off the current amplifying transistor 9.

[Effects of the Invention] As described below, the present invention provides an input voltage detection circuit and a reference voltage determination signal in a switching power supply that constitutes a control circuit power supply by providing a third winding in a voltage conversion transformer. By using a configuration in which the control circuit is turned on and off using a final signal, power consumption during normal operation can be reduced, the design voltage range of the converter transformer can be limited, the design can be made easier and smaller, and the output voltage can be This has the effect of eliminating the situation and preventing system malfunctions.

In addition, the output voltage rises due to restarting when the power supply is momentarily cut off, making it possible to prevent system runaway.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
3 is a circuit diagram showing an example of a conventional switching power supply circuit, FIG. 4 is a circuit diagram showing another example of a second conventional switching power supply circuit, and FIG. 5 is a time chart showing the operation of the embodiment shown in the figure. 5 is a timing chart showing the operation of the example of FIG. 4. FIG. 1: Input power supply 2, 3: Dividing resistor 4: Zener diode 5: Bias resistor 5: Detection transistor 7: Bias resistor 8: Feeder resistor 9: Current amplification transistor 10: Diode 11: On/off transistor 12: Filter capacitor 13: Control circuit 14: Rectifier diode 15: Voltage conversion transformer 16: Main switch 17: Rectifier diode 18: Filter capacitor 19: Voltage detection circuit

Claims (1)

[Claims] The switching power supply circuit includes a voltage control circuit, a main switch, a power exchange transformer, a secondary rectifier circuit, and a smoothing filter, and the power exchange transformer is provided with a third winding to form a power source for the control circuit. A dropper power supply is provided that is set at a voltage lower than the third winding voltage and supplies voltage from the input power supply to the control circuit through a diode, a reference voltage of the dropper power supply is supplied from the input power supply dividing resistor, and A starting circuit for a switching power supply, characterized in that the control circuit is started by a reference voltage determination signal.