JPS6173573A - Protective circuit for dc/dc converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a protection circuit for stopping the operation of a DC-DC converter when the DC load voltage drops or rises.

BACKGROUND OF THE INVENTION A conventional DC-DC converter that obtains a continuous DC load voltage Vo by DC pulses has a transistor 20 and a base 3 connected to a transistor 20 and a base 3 that operate with a power supply voltage 1, as shown in FIG. , current L, h The primary current of the lance homer 1 is intermittent. This intermittent primary current induces a voltage on the secondary side of the transformer 71.

This is rectified into an F wave by a diode 4 and a capacitor 5 to obtain a DC load voltage V. A condenser circuit 16 for monitoring is provided on the DC load voltage Vo side. A photodiode 11 constituting a seven-point quadrant 10 is connected between i[ltg and the comparator circuit 16, which is supplied to the comparator circuit 16. Further, on the negative side, the emitter of a transistor 6 for stopping operation is connected to the base 3 of the transistor 2, and a photothyristor 17 forming a pair with a photocoupler 10 on the secondary side is connected to the base 7 of the transistor 6 for stopping operation.

When the load voltage Vo decreases due to a disconnection or short circuit, the input of the comparator circuit 16 decreases, so that a current flows through the photodiode 11 of the photocoupler 10 to emit light.

Therefore, the primary side photothyristor 17 paired with the photocoupler 10 is made conductive, and the operation stop transistor 6 is turned on.
The base emitter of the Citrannostar 2, which is in a conductive state, becomes a low level due to the current flowing through the 0 base. Therefore, the operation of the transistor 2 is stopped due to a decrease in the load voltage vo, and damage to the transistor 2 is prevented in the event of an accident caused by a sustained disconnection If3A or a short circuit.

FIG. 8 shows another circuit on the secondary side of the transformer/shomer 1 in FIG.
A photodiode 11 of a photocoupler 10 is connected through the photocoupler 3, and this photodiode 11 is paired with a photothyristor 17 of the photocoupler 10 on the primary side. Furthermore, a Zener diode 15 is connected to the base of the transistor 13.

Now, when the load voltage ■o becomes an overvoltage due to a change in the load, current flows through the Zener diode 15 and turns on the transistor 13, causing the photoglymate 11 to emit light and the primary side photothyristor paired with it to emit light. 17
Since the transistor 2 is made conductive, the operation of the transistor 2 is stopped in the same way as when the load voltage vo decreases, thereby preventing damage to the transistor 2.

Problems to be Solved by the Invention Conventional over/under voltage protection circuits of this type include an arithmetic element constituting the condenser circuit 16 as electronic elements necessary for detection, and a separate circuit that supplies the photodiode 11 of the photocube 210. The photothyristor 17, which forms a pair with the photodiode 11, requires a power source E and has the drawback that it is expensive.

Means for Solving the Problems The present invention eliminates such drawbacks of the conventional art by inserting a photodiode 11 constituting a photocoupler 10 on the secondary side load voltage vo side of the transformer 1 and inserting it on the primary side of the transformer 1. A time delay capacitor and a phototransistor paired with the photodiode 11 are inserted in parallel at the gate of the transistor 6 for stopping operation to sterilize the transistor 20 gate, and a transistor is connected to both ends of the photodiode 11 and a zener is connected to its input. The present invention provides a protection circuit for a DC-DC converter configured by inserting a diode.

Operation In the protection circuit of the present invention, when the load voltage decreases, the photodiode 11 becomes below the ignition voltage and stops emitting light, and the primary side phototransistor 12 paired with the photodiode 11 is opened without receiving light. . Therefore, the base voltage of the operation stopping transistor 6 increases and becomes conductive, stopping the operation of the transistor 2, so that the operation of the converter is stopped. Also, when the load voltage increases and the voltage exceeds the Zener voltage of the Zener diode, a current flows, and the transistor that connects this Zener diode to its input becomes conductive, and the photodiode 11 connected in parallel with it becomes Stops emitting light. Therefore, the paired phototransistor 12 is opened and the operation of the converter is stopped in the same way as in the case of a voltage drop. Therefore, component circuits are protected from damage due to drops and increases in load voltage.

Embodiment The FIJ according to the present invention has a power supply voltage V1 as shown in FIG.
The current flowing to the primary side of the transformer/submer 1 is caused to flow through the transistor 2 to its base 3 and is interrupted. This intermittent current induces a voltage on the secondary side of the transformer 1, and this voltage is transferred to the diode 4.
．． The p-wave is rectified by the capacitor 5, and a DC load voltage vo is obtained. Here, a trunk star for stopping operation is connected between the base and emitter of transistor 2, and its base 7
The current is supplied through a resistor 8, and a capacitor 9 is connected between the base and emitter. A photodiode 11 forming a photocoupler 10 is still connected to the load voltage Vo side, and a phototransistor 7 nostar 12 forming a pair with this photodiode 11 and forming a photocoupler 10 is connected in parallel to the capacitor 9 on the negative side.

Now, when a current is passed through the base 3 of the transistor 2, it will be interrupted according to the period of the current flowing through the transistor 2.
The current flowing to the primary side of the transformer 1 is interrupted once,
Induces a voltage on the secondary side. This voltage is rectified by a diode 4 and E-waved by a capacitor 5 to obtain a DC load voltage Vo. However, since the capacitor 9 is inserted between the base and emitter of the trunk star for stopping the operation on the next side, even if the power supply voltage v1 is applied, the base voltage of the transistor 6 for stopping the operation is connected to the capacitor 9? ff is delayed until the load is accumulated.

However, before that, the photodiode 11 on the secondary side of the photocoupler 10 emits light, and the paired phototransistor 12 on the primary side becomes conductive, and the level between the base and emitter of the transistor 6 becomes low. becomes conductive, and transistor 2 never stops.

However, the DC load voltage ■. When the photodiode 11 drops, the photodiode 11 stops emitting light, the primary side phototransistor 12 paired with it is opened, and the transistor 6 for stopping the operation is opened.
The base voltage of 6 transistor 2 becomes low and becomes conductive, and the base voltage of 6-transnoster 2 becomes small and its operation is stopped.

Further, in FIG. 2, the emitter and collector of a transistor 13 are connected in parallel to the photodiode 11 on the load voltage Vo side, and a Zener diode 15 is inserted between its base 14 and the positive electrode of the load voltage Vo. Here, the load voltage is V. When becomes an overvoltage and exceeds the Zener voltage of the Zener diode 15, a current flows and the transistor 13 becomes conductive and the photodiode 11 stops emitting light, which causes the paired primary side phototransistor 12 to open, and as a result, in the case of an undervoltage. Similarly, the operation is stopped.

Furthermore, in order to delay the rise time of the load voltage vo from when the input voltage V is applied, and to further delay the operation of the protection circuit, a connection is made between the primary side delay capacitor 9 and the base 7 of the operation stop transistor 6, as shown in FIG. A resistor or Zener diode 15 is connected to.

In order to improve the monitoring accuracy for undervoltage in the above protection circuit, a Zener diode 15 is inserted in series with the photodiode 11 as shown in FIG. 4, or an arithmetic element is inserted on the load voltage Vo side in FIG. Insert a suitable fan/two-register circuit 16.

In the present invention, a self-excited D, such as a pro-King oscillator, constitutes the primary side of the transformer 1 with a transistor 3 and an operation stop transistor 6 as shown in FIG.
It can also be applied to a C-DC converter.

Effects of the Invention As described above, according to the present invention, without using the photocoupler 10 composed of the expensive photothyristor 17,
By using the inexpensive phototransistor 12, it is possible to prevent electronic elements and electronic equipment from being damaged by burnout.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the overvoltage protection circuit for a DC-DC converter according to the present invention in the case of undervoltage. FIG. 2 is a circuit diagram of a protection circuit in the case of overvoltage according to the present invention, FIG. 3 is a circuit diagram of a part of the primary side of the protection circuit that delays the operation of the protection circuit according to the present invention, and FIG. 4 is a circuit diagram according to the present invention. A circuit diagram of a part of the secondary side that improves the monitoring accuracy of undervoltage of the protection circuit, FIG. 5 is a circuit diagram of a part of the secondary side of another embodiment in FIG. 4, and FIG. A circuit diagram of a part of the primary side of an embodiment of the protection circuit according to Professional King oscillator, Figure 7 is a circuit diagram of a conventional protection circuit in the case of undervoltage, and Figure 8 is a circuit diagram of the conventional protection circuit in the case of overvoltage. FIG. In the figure 1 ゛ Transitoma, 2.6.13: ) Lannosta. 4, diode, 5, 9: capacitor, 10: photocoupler, 11: photodiode, 12: phototransnoster,
15: Zener diode, 16 conierator circuit,
17: Photothyristor Figure 5 Figure 6

Claims (1)

[Claims] 1. DC-D that obtains a rectified DC load voltage induced in the secondary side by a current interrupted by a pulse current input to a transistor inserted in the primary side of the transformer.
In the C converter, a photodiode constituting a photocoupler is inserted on the secondary side of the transformer, a drop in the load voltage is detected by stopping light emission, and the input of the transistor inserted on the primary side of the transformer is controlled. A DC-DC converter characterized in that a time delay capacitor and a phototransistor paired with the photodiode are inserted in parallel on the input side of an operation stopping transistor, and the input to the phototransistor is cut off and all operations are stopped. protection circuit. 2. In the DC-DC converter, a transistor is inserted between both ends of the photodiode on the secondary side of the transformer, and a Zener diode is inserted at its input, and the transistor is operated against the overvoltage of the load voltage to input the phototransistor on the primary side of the transformer. DC- according to claim 1, characterized in that the DC-
Protection circuit for DC converter.