JPH0139303B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit device that protects a transistor from overcurrent.

Transistors are generally sensitive to overcurrents, and unless they are adequately protected, they can be irreparably damaged. Therefore, if there is a risk of overcurrent, some kind of overcurrent protection circuit device is required.

FIG. 1 is a circuit configuration diagram showing a conventional example of such a transistor overcurrent protection circuit device. In the figure, 1 is a transistor, 2 is a gate control device for controlling transistor 1, and 3 is an overcurrent detection device. be. In a steady energized state, the transistor 1 receives a base current from the base control device 2 and maintains conduction.

In such a configuration, when the current flowing through the transistor 1 exceeds a predetermined value, the overcurrent detection device 3 detects this, and the base current of the transistor 1 supplied from the base control device 2 is cut off. Transistor 1 is turned off to protect against overcurrent.

However, it is difficult to protect transistor 1 from large overcurrents simply by cutting off the base current, and as the collector current increases, the collector-emitter voltage increases, resulting in power loss. It was often damaged by

This invention was made in view of the above points, and it is possible to easily turn off the transistor by temporarily shunting part or all of the current flowing through the transistor to an external circuit when an overcurrent is detected. It is an object of the present invention to provide an overcurrent protection circuit device that can cut off overcurrent and prevent destruction of transistors.

FIG. 2 is a circuit diagram showing a first embodiment of the present invention. In the figure, 4 is a reverse blocking three-terminal thyristor (hereinafter abbreviated as "thyristor"), and 5 is a reverse blocking three-terminal thyristor (hereinafter abbreviated as "thyristor"); Gate control devices 6 and 7, which are driven by the current detection device 3 and control the gate of the thyristor 4, are connected in series with the thyristor 4 through a capacitor and a resistor, respectively. 8 is a diode connected in series to the transistor 1, and 9 is a charging device for the capacitor 6. The series connection of the thyristor 4, capacitor 6, and resistor 7 is connected in parallel with the series connection of the transistor 1, overcurrent detection device 3, and diode 8.
Note that the power supply circuit and load circuit are also omitted here.

FIG. 3 is a waveform diagram of voltages and currents at various parts to explain the operation of this embodiment. Waveform a is the collector current I ₁ of transistor 1, waveform b is the collector-emitter voltage V _CE of transistor 1, and waveform c is is the output current I ₂ of the base control device 2, and waveform d is the output current of the thyristor 4.
The anode current I ₄ , the waveform e represents the output voltage V ₅ of the gate control device 5, and the waveform f represents the terminal voltage V ₈ of the diode 8. Hereinafter, the operation of the embodiment circuit of FIG. 2 will be explained using this.

In the steady state of operation (before time t ₁ in the figure), the transistor 1 conducts a predetermined collector current I ₁ under the control of the output current I ₂ of the base control device 2 . At this time, the capacitor 6 is charged to the illustrated polarity. Now, when the collector current _I1 of the transistor ₁ starts to increase due to some kind of accident at time t1, this current increase is detected by the overcurrent detection device 3, and the detected value is set in advance at time _t2 . When the predetermined value is reached, a signal is sent to the base control device 2 and the gate control device 5. This results in the output power I ₂ of the base control device 2 being supplied to the base of the transistor 1 at the time t ₂
At the same time, the output voltage V ₅ is output from the gate control device 5 and triggers the gate of the thyristor 4 .

As described above, since the capacitor 6 is charged to the polarity shown, when the gate of the thyristor 4 is triggered, the charge in the capacitor 6 is discharged through the resistor 7, the thyristor 4, and the power supply circuit and load circuit (not shown). The overcurrent of transistor 1 is bypassed. In this way, the collector current I ₁ of transistor 1 becomes zero at time t ₃ . Thereafter, until time t ₄ , the overcurrent in the main circuit flows through the path consisting of capacitor 6 , resistor 7 and thyristor 4 and does not flow through transistor 1 .

After the current I ₂ to the base of transistor 1 is cut off at time t ₂ , transistor 1 begins to regain its collector-emitter current blocking ability,
Since the collector current I ₁ decreases and the collector current I ₁ of the transistor 1 is briefly cut off between time points t ₃ and _{t 4} , the current blocking ability between the collector and emitter is quickly restored. After time _t4 , the capacitor 6, which has finished discharging its charge at time _t4 , is charged to a polarity opposite to that shown in the figure due to the overcurrent of the main circuit. Therefore, there is a voltage between the collector and emitter of transistor 1.
V _CE is applied again, but at this point the current blocking ability has been restored, so the collector current I ₁ does not flow. Then, at time _t5 , capacitor 6 is charged to a value substantially equal to the power supply voltage with the polarity opposite to that shown in the figure, and at time _t6, the overcurrent becomes zero. In this way, the transistor 1 easily recovers its current blocking ability, so that the overcurrent can be completely cut off. The resistor 7 suppresses the current I ₄ of the thyristor 4, and may be omitted depending on the case.

Here, the diode 8 functions to prevent an overvoltage from being directly applied to the transistor 1 from the shunt circuit including the thyristor 4, and is a so-called overvoltage prevention diode. In addition, the current that is shunted to the above shunt circuit is
When the transistor 1 detects an overcurrent,
This is to make the thyristor 4 connected in parallel conductive, thereby promoting recovery of the current blocking ability of the transistor.

FIG. 4 is a circuit configuration diagram showing a second embodiment of the present invention, in which 10 represents a load and 11 represents a power source. In this embodiment, when the transistor 1 is operating normally, the capacitor 6 is charged to the required polarity with the voltage across the load 10, and the charging device 9 in the first embodiment is not required. I don't. The overcurrent cutting operation of this circuit is similar to that of the first embodiment.

FIG. 5 is a circuit configuration diagram showing a third embodiment of the present invention, in which the present invention is applied to a so-called inverter circuit, in which 1a, 1b, 1c and 1d are transistors, and 12 is a circuit impedance.
That is, the inverter converts the DC power from the DC power supply 11 into AC power and supplies the AC power to the load 10, and the operation of this inverter does not require further explanation.

In this third embodiment, transistor 1a
When an overcurrent flows through the transistors 1a to 1d, the overcurrent detection device 3 detects this and causes the base current control device 2 to cut off the base current of the transistors 1a to 1d, and the gate control device 5 The gate of thyristor 4 is triggered to make it conductive. As explained in the first embodiment, the power supply 11 is temporarily short-circuited by the circuit including the capacitor 6, the resistor 7, and the thyristor 4 to restore the current blocking ability of the transistors 1a to 1d, and then each transistor 1a ~1d from overcurrent.

In the above embodiment, a thyristor is used to control the current to the capacitor 6, but the switching element is not limited to a thyristor, and other switching elements may be used.

As detailed above, in the present invention, a series connection body of a capacitor and a switching element is connected in parallel to a protected transistor, and when an overcurrent of the transistor is detected, the base current of the transistor is quickly cut off. At the same time, since the switching element is made conductive and the current of the transistor is shunted to the series connection body, the current blocking ability of the transistor is rapidly restored, the overcurrent is safely cut off, and the transistor is prevented from being destroyed. can be prevented.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional device, Fig. 2 is a circuit diagram showing a first embodiment of the present invention, and Fig. 3 is a diagram showing voltages and currents at various parts to explain the operation of the first embodiment. The waveform diagram, FIGS. 4 and 5 are circuit configuration diagrams showing second and third embodiments of the present invention, respectively. In the figure, 1 is a transistor, 2 is a base control device, 3 is an overcurrent detection device, 4 is a thyristor (switching element), 5 is a gate control device, 6 is a capacitor, 11 is a power supply, and 12 is a load. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A protected transistor, a forward diode connected in series with the transistor, an overcurrent detection device connected in series with the protected transistor,
A base control device that cuts off the base current of the protected transistor by a signal from the overcurrent detection device when an overcurrent is detected by the overcurrent detection device; A capacitor and a switching element connected to each other in series, a resistor connected in series to the switching element, a charging device that charges the capacitor with a voltage of opposite polarity to the voltage applied across the protected transistor, and 1. A transistor overcurrent protection circuit device comprising: a gate control device that triggers the gate of the switching element by a signal from the overcurrent detection device when an overcurrent is detected by the current detection device. 2 The load, the overcurrent detection device, the protected transistor and the forward diode are connected in series, the resistor and the switching element are connected in series, and these two
By connecting two series circuits in parallel with each other,
A capacitor is connected between the connection point between the resistor and the switching element and the connection point between the load and the overcurrent detection device, and the base current of the protected transistor is interrupted by the signal from the overcurrent detection device. and a gate control device that triggers the gate of the switching element by a signal from the overcurrent detection device when an overcurrent is detected by the overcurrent detection device. Current protection circuit device.