JPS61147773A - Overcurrent protecting circuit of gate turn off thyristor - Google Patents

Abstract

PURPOSE:To protect an overcurrent rapidly with a simple structure by connecting a current detecting resistor in series with the cathode side of a GTO, and inserting a diode between the gate of a GTO turning OFF thyristor and the cathode of the GTO. CONSTITUTION:An overcurrent protecting circuit of a GTO1 omits an overcurrent detector, connects the first diode 31 between the cathode of the CTO1 and the gate of a thyristor 16, and connects the second diode 32 between a parallel circuit of a capacitor 15 and a resistor 14 provided at the collector of a transistor Q1 of a drive circuit 5' and the gate of the thyristor 16. Thus, when the detected voltage by a current detecting resistor 4 exceeds the prescribed value E4, the voltage is applied to the gate of the thyristor 15 directly through the first diode 31. Thus, the turning ON current is forcibly flowed irrespective of the control pulse signal output of a drive controller 9 to turn ON the thyristor 16 and to turn OFF the GTO1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an overcurrent protection circuit for gate turn-off thyristors (hereinafter abbreviated as GTO) used in power conversion devices such as inverters and choppers.

[Technical background of the invention]

FIG. 3 shows a conventional example of an overcurrent protection circuit for a GTO. That is, the anode of the GTO is connected to the positive electrode of the DC power supply 3 via the load circuit 2, and the cathode is connected to the current detection resistor 4.
The gate is connected to the output terminal of the drive circuit 5, and the anode is grounded via a capacitor 6 and a resistor 7 in series.

The voltage across the current detection resistor 4 is guided to an overcurrent detection circuit 8, the detection output signal of this detection circuit 8 is guided to a drive control circuit 9, and the output signal of this drive control circuit 9 is transmitted to the overcurrent detection circuit 8. It is led to the input end. In this drive circuit 5, an input terminal 10 is connected to the base of an NPN transistor Q and is grounded via a resistor 11. The emitter of this transistor Q is grounded, and the collector is connected to a drive circuit power supply terminal 13 via a resistor 12. Further, the collector is connected to the cand of a GTO turn-off thyristor 16 through a resistor 14 and a capacitor 15 in parallel, and is grounded through a resistor 17 and a capacitor 18 in parallel. The thyristor 160 cathode is grounded and the anode is PN
It is connected to the collector of a P-type transistor Q.

This transistor Q.

The emitter of is connected to the power supply terminal J3 through a resistor 19, and the base thereof is connected to the power supply terminal 13 through a resistor 20, and the transistor Q is connected through a resistor 21 to the power supply terminal J3.
connected to the collector. The anode of the thyristor 16 is connected to the drive circuit output terminal 24 via a Zener diode 22 in the opposite direction and then via a resistor 23.
A capacitor 25 is connected in parallel to the series circuit of No. 3.

Next, the operation of the above circuit will be explained with reference to FIG. When the control pulse signal applied from the drive control circuit 9 to the base of the transistor Q1 becomes high level "H#,"
Transistor Q1 turns on, and transistor Q!
The base potential drops and turns on. Conversely, when the control pulse signal becomes low level "L", the transistor Q is turned off, and the base potential of the transistor Q rises, turning it off. Therefore, the base potential of the transistor Q changes. Thyristor 16 depending on
The gate current changes, and the thyristor 16 turns on and off. When the transistor Q is turned on, GTOJ (7
) The current I, s from the capacitor 25 and the current ts from the series circuit of the Zener diode 22 and the resistor 23 flow through the gate as turn-on current, so the GTO
1 is turned on, 7 node current flows, the anode voltage decreases, and a detection voltage corresponding to the above-mentioned anode current is generated in the current detection resistor 4. Note that at this time, the thyristor 16 is in an off state.

On the other hand, when the transistor Q1 is turned off, the current 1111 from the capacitor 15 and the current 114 from the resistor 14 flow as turn-on currents to the gate of the thyristor 16, so that the thyristor is turned on. At this time, the capacitor 25 connected to the gate of the GTO1 and charged when it was turned on
Since the charge is discharged as a discharge current through the thyristor 16, a turn-off current flows through the gate of GTOI, which becomes the ground potential, and GTOl is turned off. In addition,
After that, when the transistor Q1 is turned on, the electric charge previously charged in the active capacitor 15 is discharged through the transistor Q.

Then, during the operation of c'ro1 as described above,
When the load circuit 2 suddenly fluctuates and the anode current of the GTOI flows to a value greater than a predetermined value, the detection voltage of the current detection resistor 4 exceeds the predetermined value E4 and becomes, for example, E4'. When the overcurrent detection circuit 8 detects the detection voltage IC, / at the time of overcurrent, the drive control circuit 9 is configured to turn off the GTOl by setting the control pulse signal to a low level and turning on the thyristor 16. Control takes place.

[Problems with background technology]

By the way, since the delay time Δt from when the overcurrent detection circuit 8 detects an overcurrent to when c'ro1 is actually turned off cannot be ignored, especially when the rising speed d1/dt of the anode current of GT0 is large, GTOf In order to quickly perform turn-off control within the maximum turn-off current of , it was necessary to keep the overcurrent detection current value low.

However, this narrows the steady-state operating current range of the GTOJ, and it is often impossible to fully utilize the current capability of the GTOI.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and provides an overcurrent protection circuit for a gate turn-off thyristor that can quickly turn off the GTO when an overcurrent occurs in the GTO anode current and has a simple configuration. It is something.

[Summary of the invention]

That is, the GTO overcurrent protection circuit of the present invention connects a current detection resistor in series to the cathode side of the GTO, and controls the GTO in a drive circuit that turns on and turns off the GTO according to the logic level of a control pulse signal input. It is characterized in that a diode is inserted and connected between the gate of the 'I'O turn-off thyristor and the cathode of the GTO.

As a result, the diode is turned on by the detection voltage generated in the current detection resistor at the time of GTO overcurrent,
By forcibly turning on the thyristor regardless of the control pulse signal input, it is possible to turn off the GTO. Therefore, with a very simple circuit configuration, overcurrent protection can be quickly performed with a delay of only the operating time of the diode and thyristor from the time when overcurrent occurs.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. Compared to the conventional example described above with reference to FIG. 3, the GTO overcurrent protection circuit shown in FIG.
A first diode 31 is additionally connected in the forward direction between the gate of the transistor Q and the gate of the transistor Q in the drive circuit 5'.

The difference is that a second diode 32 is additionally connected in the forward direction between the parallel circuit of the capacitor 15 and the resistor 14 connected to the collector of the above circuit and the gate of the above-mentioned cyrisk 16, and other things are the same. The same reference numerals as those in the middle are given, and the explanation thereof will be omitted.

The operation of the circuit described above is as shown in FIG. 2, and is the same as that of the conventional example described above with reference to FIG. 4, except for the overcurrent protection operation, so a description thereof will be omitted. That is, when the voltage detected by the current detection resistor 4 exceeds the predetermined value E4 at the time of overcurrent of the GTO anode current and reaches, for example, the voltage value B, /, the detected voltage E, / at this time passes through the first diode 31. It is applied directly to the gate of thyristor 16. As a result, regardless of the control pulse signal output of the drive control circuit 9, the turn-on current Ill is forced to flow through the first diode 31 to the gate of the thyristor 16 due to the detection voltage E4', and the thyristor 16 is turned on. Since G'I'01 is turned off, the operating current of GTOJ is always kept within a constant range. At this time, the transistor Q+ is in the on state and its collector potential is low, which reverse biases the second diode 32 and puts it in a high impedance state.
The thyristor turn-on current from the first diode 31 is prevented from flowing to the transistor Q1 side.

In the above-mentioned overcurrent protection operation, the time ΔL' from the point of overcurrent until the GTOJ is forcibly turned off
is an extremely short time required for the first diode 310 to turn on and the thyristor 16 to turn on, and the increase in the G'l'0 anode current during this period is extremely small. In other words, c'roz turns off immediately when an overcurrent occurs, so G
Even when the rising speed of TO anode current is fast, 1&
Big 1-7 Oh 71! ! Turn-off control is quickly performed within i. Further, the above-mentioned overcurrent protection operation is realized by a very simple circuit configuration in which the overcurrent detection voltage E,/ is applied to the gate of the GTO turn-off thyristor 16 through the first diode 31.

The GTO anode current value at which the overcurrent protection operation starts can be easily changed by changing the resistance value of the current detection resistor 4, the forward voltage VF of the first diode 3, etc. be.

〔Effect of the invention〕

As described above, according to the GTO overcurrent protection circuit of the present invention, the GTO can be quickly turned off when an overcurrent occurs in the GTO anode current with an extremely simple circuit configuration, and the current capacity of the GTO can be fully utilized. Therefore, the steady-state operating current region can be utilized.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the GTO overcurrent protection circuit according to the present invention, Fig. 2 is a timing waveform diagram showing the circuit operation of Fig. 1, and Fig. 3 is a conventional GTO overcurrent protection circuit. A circuit diagram showing the circuit, and FIG. 4 is a timing waveform diagram showing the circuit operation of FIG. 3. 1...GTO, 4...Resistor for current detection, 5'...
Drive circuit, 16...thyristor, 31...diode. Applicant's representative Patent attorney Takehiko Suzue Figure 1, 75'

Claims (1)

[Claims] The gate turn-off thyristor has a current detection resistor connected in series to the cathode side, and a thyristor that operates on and off depending on the logic level of the control pulse signal input. Turn-on and turn-off drive of turn-off thyristor,
A drive circuit that performs this turn-off drive by a turn-on operation of the thyristor, and a drive circuit that is inserted and connected between the cathode of the gate turn-off thyristor and the gate of the thyristor, detects a current detection resistor that is generated in the current detection resistor when the gate turn-off thyristor overcurrent occurs. 1. An overcurrent protection circuit for a gate turn-off thyristor, comprising a diode that is turned on by voltage to supply a turn-on current to the thyristor.