JPS5989570A - Gate circuit for self-extinguishing type controlled rectifier - Google Patents

Abstract

PURPOSE:To suppress a reverse voltage between the gate and the cathode of a controlled rectifier by controlling a variable impedance element connected between a DC power source and the gate electrode or cathode electrode of the rectifier. CONSTITUTION:In order to turn ON an SI thyristor 1, a positive gate current is supplied to the thyristor 1 in a circuit of the positive terminal of a DC power source 11, a resistor 12, the thyristor 1, a turn ON switch 13 and the negative terminal of the power source 11. In order to turn OFF the thyristor 1, the switch 13 is opened, and a turn OFF switch 8 is closed. At this time the impedance between the drain and the source of an FET7 becomes very small level, and a gate reverse current is supplied to the thyristor 1 in a circuit of the positive terminal of the power source 2, a resistor 6, an FET7, the thyristor 1 and the negative terminal of the power source 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention supplies a turn-off current pulse to a self-extinguishing controlled rectifier element (hereinafter simply referred to as the controlled rectifier element 2) such as an electrostatic induction thyristor (hereinafter referred to as an SI thyristor) or a gate turn-off thyristor. The invention relates to a gate circuit for

In recent years, as the performance of controlled rectifying elements has improved and their capacity has increased, the voltage of the DC power supply that serves as the pulse source has become particularly important when creating a large current pulse that requires a fast rise and a large peak value, especially for turn-off current pulses. It is advantageous to choose a high value. However, in this case, it has not been possible to increase the power supply voltage very high because it is limited by the value of the reverse breakdown voltage between the gate and cathode of the controlled rectifier.

In view of the above-mentioned points, the present invention provides a special gate that can supply a large current pulse from a high-voltage DC power supply at the early stage of turn-off, and apply an appropriate gate reverse voltage from the end of turn-off to the off period. It provides a circuit. Hereinafter, the present invention will be explained based on the drawings. Here, we will mainly explain the 8I thyristor as an example.The 8I thyristor has an anode (A) and a cathode (K) in the same way as a normal reverse blocking three-terminal thyristor.

This is a switching element having three gate (G) electrodes, as shown in FIG. Here, Figure 1(a)
, (b) is an explanatory diagram showing an SI thyristor and its static characteristic diagram.

As shown in the figure, the static characteristics of the 8I thyristor are different from those of the normal type, and the gate-cathode voltage vGK is zero (VGK=O
), when the anode-cathode voltage vλK is below a certain value vBo, it exhibits a blocking characteristic, and when the anode-cathode voltage YAK exceeds the value vnol, it becomes a breakdown characteristic in which the anode current increases rapidly, and eventually turns on. In addition, by setting the gate-cathode voltage vGK to a negative voltage, as shown in the example < (VGIC=V
1<0) P (VBI>VBO), the blocking voltage between the anode and cathode can be increased.

Furthermore, the gate-cathode voltage VGIC is set to positive (V
It can be turned on by setting oic=Vg>O). Therefore, to properly control the 8I thyristor, it is necessary to supply a negative gate-to-cathode voltage during the OFF period and a positive gate-to-cathode voltage during the ON period. Note that some SI thyristors have so-called normally-on characteristics that turn on when the voltage between the gate and cathode is zero, and those that have normally-off characteristics that show a high blocking voltage even when the voltage between the gate and cathode is zero. Those having intermediate characteristics as shown in FIG. 1 are common.

Next, FIG. 2 shows typical switching operation waveforms of an 8I thyristor.

That is, at time To, the gate-cathode voltage V
If GK is positive, the gate current is 1. is also positive, and the anode current IA rises with an appropriate delay time to complete turn-on. During this on period, the gate-to-cathode voltage VGK is about 1 port, and the gate current is 1. is generally small.

In addition, the gate (
When G) is negatively biased, the gate current IG first rises in the negative direction, and at time T2, the anode current Em and the gate-cathode voltage VOX begin to decrease. Then, at time T3, gate current IO+gate
The cathode voltage ■GK *The rapid drop in the anode current Em ends, and thereafter they decrease relatively smoothly until time T4, completing turn-off. Here, gate current I
In order to shorten the turn-off time, a negative polarity pulse such as (Tt≦T<Ti) is required to have a fast rise and a high peak value. In the case of approximately ampere, the gate current at time T1 is 1. is (-200 to -300) amperes, and the time from time TI to time T3 is about 1 to 2 μs.

A simple method for obtaining high-speed, large-current pulses as shown in b is to use a gate transformer, which is in fact often used in gate circuits for gate turn-off thyristors. However, when this is used for SI thyristors, the following problems occur. That is, the SI thyristor becomes a controlled rectifying element that is nearly an order of magnitude faster than the gate turn-off thyristor. Therefore, the time requirement for the gate reverse current is severe, and even a slight leakage inductance of the gate transformer becomes a problem, and the gate transformer itself becomes extremely expensive, so it cannot be easily implemented.

Another promising method is to create a DC power source using a power transformer, etc., connect capacitors in parallel to reduce impedance at high frequencies, and then short-circuit this capacitor with a switching element to obtain high-speed, large-current pulses. According to this method, the current rise is limited due to the floating inductance present in the circuit, making it difficult to obtain a satisfactory pulse. Although this can be greatly improved by increasing the power supply voltage, since the reverse impedance between the gate and cathode of the SI thyristor at the end of turn-off is extremely large, the power supply voltage must be increased. Since almost all of the voltage is applied between the gate and the cathode, it is impossible to increase the reverse breakdown voltage between the gate and the cathode.

Fig. 3 is shown to facilitate understanding of the technical idea of the present invention, in which 1 is an SI P filter as shown in Fig. 1, 2 is a DC power supply, and 3 is a resistor for controlling the voltage of the DC power supply 2. 4 and a variable impedance element for applying a partial voltage between the gate and cathode of the SI thyristor 1, 5
is a voltage detection circuit that detects the voltage between the gate and cathode of the SI thyristor 1 and controls the impedance amount of the variable impedance element 3 using the output thereof. Here, the DC power source 2 may be formed by cutting off the AC power source as described above using a power transformer, rectifying and filtering it, and reducing the impedance using a capacitor.

However, the operation of the product thus constructed is as follows.

Now, in the initial turn-off period from time TI to time T2 shown in FIG. 2, the gate impedance of the 8I thyristor 1 is low, and the gate-cathode voltage is also a small value. The impedance of the variable impedance element 3 is controlled to a low value by the voltage detection circuit 5 capable of detecting this.The voltage of the DC power source 2 is selected to be high in advance, so that the impedance of the variable impedance element 3 is controlled to a low value. ．． Even if impedance between the gate and cathode of the SI thyristor 1, floating inductance in the circuit, etc. exist, a high-speed, large-current reverse gate current can be supplied to the 8I thyristor 1.

Further, as the turn-off operation progresses, the time T shown in FIG.
2) During the period corresponding to time T3, the reverse impedance between the gate and cathode of the 8I thyristor 1 gradually increases, and the reverse voltage between the gate and cathode also increases.
If left as is, almost the entire voltage of the DC power supply 2 will be applied between the gate and cathode.

However, this must be avoided due to limitations on reverse withstand voltage between gate and cathode. Therefore, the voltage detection circuit 5 detects an increase in the gate-cathode voltage in the reverse direction, and increases the impedance of the variable impedance element 3 in accordance with this value.

Therefore, by controlling the impedance of the variable impedance element 3 in this way, together with the resistor 4, the voltage of the DC power supply 2 can be divided into appropriate values and suppressed to below the reverse breakdown voltage. In order to maintain the off state even during the off period after the end of turn-off, it is necessary to set the voltage between the gate and cathode to a negative value as shown in FIG. 1 (VGK=V1). here,
Even though it is not possible to increase the impedance of the variable impedance element 3 to a value close to infinity, the reverse impedance between the gate and cathode of the 8I thyristor 1 during the off period is very high, and the value is quite high together with the resistance value of the resistor 4. It is possible to do up to Furthermore, the loss flowing from the variable impedance element 3 to the resistor 4 during the off period can be made so small that it can be practically ignored.

As described above, according to this technical idea, it is possible to supply a high-speed, large-current pulse from a high-voltage DC power supply at turn-off, and furthermore, it is possible to continuously apply an appropriate gate reverse bias with low loss. Further, the present invention will be explained in detail using specific examples.

FIG. 4 is a connection diagram of a specific example according to the present invention.
9, 10, and 12 are resistors, 7 is a field-effect transistor (hereinafter referred to as FET) shown as an N-channel power MOS type example, and 8 is an 8I thyristor 1.
11 is a DC power supply for supplying a positive bias to the gate of the SI thyristor 1, and 13 is a turn-on switch. In the figure, the same reference numerals as in FIG. 3 indicate parts having the same function. Here, the FET 7 corresponds to the variable impedance element 3 shown in FIG. In addition, turn-off switch 8 and turn-on switch 1
31! :L, various types of transistors, photocouplers, etc. may be used.

The operation of the thyristor 1 (gate cathode) → turn-on switch 13 → DC power source 1
A positive gate current may be supplied to the S ethyristor 1 from the negative electrode path of the S ethyristor 1.

Here, the resistor 12 is arranged to limit the positive gate current. The voltage between the gate and the cathode during the on period is small as shown in FIG. 2, and the loss caused by the resistor 12 is also very small. Also, since the turn-off switch 8 is open, the gate electrode (G) of the PET 7 has the same potential as the gate of the 8I thyristor 1 through the resistor 10, and the source electrode (8) of the FBT 7
FET 7 is connected to the cathode of thyristor 1.
The gate-source voltage of 8I thyristor 1 is
0 becomes the same as the voltage between the cathodes.Here, as is well known (FE
The threshold voltage of T7 is about 2 to 4 volts. From this, when the gate-source voltage of FET7 is about 1 volt, the impedance between the drain and source (D-8) is close to infinity, so the DC power supply 2
has no effect on circuit operation during the on period.

Further, in order to turn off the 8I thyristor 1, the turn-on switch 13 is closed, and the turn-off switch 8 is closed. Here, since the voltage between the gate and cathode of the SI thyristor 1 at the early stage of turn-off is maintained at a small value, by appropriately selecting the values of the resistors 9 and 10, FF! T? It is obvious that the gate-source voltage of 0 can be increased to a value higher than the threshold voltage.
Therefore, by making the impedance between the drain and source of FET 7 very small, the positive electrode of DC power supply 2 → resistor 6
→FF! A gate reverse current is supplied to the 8I thyristor 1 through the path T7 (D-8)→8I thyristor 1 (cathode-gate)→the negative electrode of the DC power supply 2.

Resistor 6 is for current limiting like resistor 12, but this is because the gate reverse current requires a much larger value than the forward current I, so it generally only needs to be very small.Furthermore, the turn-off operation is As the voltage between the gate and cathode of the 8I thyristor 1 increases in the negative direction as described above, the source potential of the FET 7 also increases with respect to the gate side, and the voltage between the gate and source decreases. Therefore, the impedance between the drain and source of the FET 7 also increases, and eventually a balanced state is reached when the voltage between the gate and source approaches the threshold voltage.

In this balanced state, the gate-source voltage VG8 of FET 7 and the gate-source voltage VG8 of SI thyristor 1 are determined.
The relationship between the cathode voltage (GK) is shown as follows, assuming that the resistance values of the resistors 9 and 10 are R11m RIG, and the voltage of the DC power supply 2 is VGN13.

Note that since the gate-cathode voltage vex is a small value of about several volts, by selecting the resistance value R11v RIG, the gate-cathode voltage VOX is set to an appropriate negative voltage that is necessary to maintain the off state and is below the reverse breakdown voltage. Obviously it can be a value.

Furthermore, if we assume that the drain-source impedance of FIT 7 is R7 and the resistance values of resistors 4 and 6 are R4#R6, then if we ignore the gate-cathode impedance of 8I thyristor I, then It is important that R7 and vGx are expressed by the formula (11
, (21), it can be said that the gate-source voltage VG8 of FET 7 is determined to be a value that satisfies (21). Therefore, resistors 9 and 10 and FET 7 are
It can be said that this circuit constitutes a circuit corresponding to the voltage detection circuit 5 shown in the figure. Furthermore, since the resistance value R4 can be selected to be large, the drain-source impedance R7 of the PET 7 can also be increased, according to equation (2), and the gate-source voltage VG8 when turned off can be reduced to a threshold value. The loss generated in the FET 7 and other parts when the voltage is close to the SiGold voltage can be minimized. Furthermore, it is desirable that the value of the resistor 9.10 be small in order to speed up the operation of the FET 7. However, since this increases the loss, in practice, countermeasures may be taken such as setting both values to relatively large values and further providing a capacitor in parallel with the resistor 9 for speeding up. In addition, during the off period, the turn-on switch 13
It is clear that the DC power supply 11 does not cause any trouble because it is open-circuited.

As explained above, according to the present invention, a high-voltage DC power supply is used to provide a high-speed, large-current turn-off gate pulse, and a variable impedance element provides an appropriate reverse bias voltage lower than the power supply voltage. It is possible to provide a device having a circuit configuration. In addition, in FIGS. 1 to 4, the description has been made with reference to the SlPI3 iris, but the present invention is not limited thereto, and can be applied to other controlled rectifier elements such as gate turn-off thyristors. Since the gate current required to operate is almost the same as that of the SI thyristor, it goes without saying that it can be applied based on the same principle.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the SI thyristor and its static characteristic diagram,
Fig. 2 is a diagram showing typical switching operation waveforms of an 8I thyristor, Fig. 3 is a circuit diagram shown to facilitate understanding of the technical idea of the present invention, and Fig. 4 is a diagram showing a specific example of the present invention. It is a connection diagram. 1-... Electrostatic induction thyristor (SI thyristor), 2
゜11...DC power supply, 3...Variable impedance element,...Turn-on switch, 1 person...
...Anode current, ■λK...Anode-cathode voltage s VGK...Gate-cathode voltage, IG...Gate current. 1st Fertilization (oL) (b) Vt+y Gen 2 Figure

Claims (1)

[Claims] A DC power source that supplies a negative polarity current to the gate electrode of the controlled rectifying element with a voltage value exceeding the reverse withstand voltage between the gate and cathode of the controlled rectifying element; A variable impedance element connected between the elements and a voltage detection circuit that detects a reverse voltage between the gate and cathode of the controlled rectifier are provided, and the impedance of the variable impedance element is controlled by obtaining the output of the voltage detection circuit. 1. A gate circuit for a self-extinguishing control rectifier, characterized in that the gate circuit is configured to suppress reverse voltage between the gate and cathode of the rectifier.