JPH0250709B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 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.

Conventional technology Conventionally, continuous DC load voltage is generated by DC pulses.
As shown in Figure 7, the DC-DC converter that obtains V ₀ has a transistor 2 that operates with the power supply voltage V ₁ .
A pulse current is passed through the base 3 of the transformer 1 to intermittent the primary current of the transformer 1. This intermittent primary current induces a voltage on the secondary side of the transformer 1, which is rectified by the diode 4 and capacitor 5 to obtain a DC load voltage V ₀ , and is also monitored on the DC load voltage V ₀ side. A comparator circuit 16 is provided for this purpose. A photodiode 11 forming a photocoupler 10 is connected to the power supply E supplied to the comparator circuit 16.
is connected. There is also a transistor 2 on the primary side.
The emitter of the transistor 6 for stopping the operation is connected to the base 3 of the transistor 6, and the photothyristor 17 which forms a pair with the photocoupler 10 on the secondary side is connected to the base 7 of the transistor 6 for stopping the operation.

When the load voltage V ₀ 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 a current flows through the base of the operation stopping transistor 6, thereby making it conductive and the base emitter of the transistor 2 becomes a low level. Therefore the load voltage
The reduction in V ₀ causes the transistor 2 to stop operating, thereby preventing damage to the transistor 2 in the event of an accident caused by a sustained disconnection or short circuit.

Also, Figure 8 shows the transformer 1 in Figure 7.
The photodiode 11 of the photocoupler 10 is connected between the lines of the load voltage V ₀ rectified by the diode 4 capacitor 5 through the transistor 13, and this photodiode 11 is connected to the primary side. It is paired with the photothyristor 17 of the photocoupler 10. Further, a Zener diode 15 is connected to the base of the transistor 13.

When the load voltage V ₀ becomes an overvoltage due to a change in the load, current flows through the Zener diode 15 and makes the transistor 13 conductive, causing the photodiode 11 to emit light and the primary side photothyristor paired with it to emit light. 17 is conductive, so
Similarly to when the load voltage V ₀ decreases, the transistor 2 stops operating to prevent damage to the transistor 2.

Problems to be Solved by the Invention The conventional over/under voltage protection circuit of this type requires a separate power supply E to be supplied to the arithmetic element constituting the comparator circuit 16 and the photodiode 11 of the photocoupler 10 as electronic elements necessary for detection. In addition, the photothyristor 17 forming a pair with the photodiode 11 has the disadvantage of being expensive.

Means for Solving the Problems The present invention eliminates such drawbacks of the conventional method by inserting a photodiode 11 constituting the secondary side load voltage V ₀ side of the transformer 1, and
A time delay capacitor and a phototransistor paired with the photodiode 11 are inserted in parallel to the gate of the operation stop transistor 6 that controls the gate of the transistor 2 inserted on the primary side, and a transistor is connected to both ends of the photodiode 11. Configure by inserting Zener diode 4 into its input.
It provides a protection circuit for DC-DC converters.

Function 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 does not receive light and is opened. Ru. Therefore, the base voltage of the operation stopping transistor 6 increases and becomes conductive, thereby stopping the operation of the transistor 2, thereby stopping the operation of the converter. 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 this is short-circuited and emits light. stop. The paired phototransistor 12 is therefore 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 drop or rise in load voltage.

Embodiment In an embodiment of the present invention, as shown in FIG.
The current flowing to the primary side of the transformer 1 due to V ₁ is passed through the transistor 2 and a pulse current is applied to the base 3 of the transistor 1 to intermittently cause the current to flow intermittently. This intermittent current induces a voltage on the secondary side of the transformer 1, and this voltage is rectified by a diode 4 and a capacitor 5 to obtain a DC load voltage _V0 . Here, a transistor 6 for stopping operation is connected between the base and emitter of the transistor 2, a current at the base 7 is supplied through a resistor 8, and a capacitor 9 is connected between the base and emitter. Further, a photodiode 11 forming a photocoupler 10 is connected to the load voltage V ₀ side, and a phototransistor 12 forming a pair with the photodiode 11 and forming a photocoupler 10 is connected in parallel to the capacitor 9 on the primary side.

Now, when a pulse current is applied to the base 3 of the transistor 2, the transistor 2 is turned on and off according to the period of the pulse, and the current flowing through the primary side of the transformer 1 is turned on and off, thereby inducing a voltage on the secondary side. This voltage is rectified by a diode 4 and waved by a capacitor 5 to obtain a DC load voltage V ₀ . However, since the capacitor 9 is inserted between the base and emitter of the primary-side operation-stopping transistor 6, even when the power supply voltage _V1 is applied, the base voltage of the operation-stopping transistor 6 is delayed until charge is accumulated in the capacitor 9. 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.
During normal use, transistor 6 is conductive and transistor 2 is never turned off.

However, when the DC load voltage V ₀ decreases, the photodiode 11 stops emitting light, the primary-side phototransistor 12 paired with it opens, and the base voltage of the operation stop transistor 6 increases and becomes conductive, causing the transistor 2 to become conductive. The base voltage of becomes small and stops its operation.

Further, in FIG. 2, the emitter and collector of a transistor 13 are connected in parallel with the photodiode 11 on the load voltage V ₀ side, and a Zener diode 15 is inserted between its base 14 and the positive electrode of the load voltage V ₀ . Here, when the load voltage V ₀ becomes an overvoltage and exceeds the Zener voltage of the Zener diode 15, a current flows to conduct the transistor 13 and the photodiode 11 stops emitting light. The result is that operation is stopped as in the case of undervoltage.

Furthermore, in order to delay the rise time of the load voltage V ₀ from when the input voltage V ₁ is applied and 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 between them.

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 connected to the load voltage V ₀ side in FIG. A comparator circuit 16 like this is inserted.

The present invention can also be applied to a self-excited DC-DC converter such as a blocking oscillator which has a transistor 3 and an operation stop transistor 6 as shown in FIG. 6 and constitutes the primary side of a transformer 1.

Effects of the Invention As described above, according to the present invention, the inexpensive phototransistor 12 is used without using the photocoupler 10 composed of the expensive photothyristor 17, thereby preventing burnout and damage to electronic elements and electronic equipment. be able to.

[Brief explanation of drawings]

FIG. 1 shows a circuit in the case of undervoltage of an embodiment of the overvoltage and undervoltage protection circuit for a DC-DC converter according to the present invention.
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 partial circuit diagram of the primary side of an embodiment of a protection circuit in a blocking 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: transformer, 2, 6, 1
3: transistor, 4: diode, 5, 9: capacitor, 10: photocoupler, 11: photodiode, 12: phototransistor, 15: Zener diode, 16: comparator circuit, 17: photothyristor.

Claims (1)

[Claims] 1. In a DC-DC converter that obtains a rectified DC load voltage induced on the secondary side by a current interrupted by a pulse current input to a transistor inserted on the primary side of a transformer. , a photodiode constituting a photocoupler is inserted on the secondary side of the transformer, and a drop in the load voltage is detected by stopping light emission, and an operation stopper is used to control the input of the transistor inserted on the primary side of the transformer. A protection circuit for 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 a transistor, and the input of the phototransistor is cut off to stop all operations. . 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 in response to an overvoltage of the load voltage to control the input of the phototransistor on the primary side of the transformer. A protection circuit for a DC-DC converter according to claim 1, characterized in that the protection circuit for a DC-DC converter is cut off and stops all operations.