JPS59165958A - Snubber circuit of self-extinguishing type semiconductor element - Google Patents

Abstract

PURPOSE:To reduce the loss without decreasing the efficiency at the normal time by reducing a snubber capacitor at a light load time. CONSTITUTION:When the turning OFF current of a GTO1 is small, a Zener diode 20 does not conduct, and transistors 17, 22 hold OFF state. A thyristor 14 remains OFF. When the turning OFF current of the GTO1 becomes large, a current is flowed to the diode 20, a transistor 22 is conducted, a transistor 17 is conducted, and the thyristor 14 is fired. When the thyristor 14 is fired, a capacitor 12 is connected as a snubber circuit.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a gate turn-off thyristor (hereinafter referred to as a GTO).
), etc., and particularly relates to a snubber circuit for preventing destruction due to overvoltage applied to the GTO during turn-off.

[Technical background of the invention and its problems]

FIG. 1 shows a general example of a GTO and its attached snubber circuits.

First, the turn-off time of GTO/ will be explained. GT
To turn off O/, give a turn-off signal to the pace of transistor O, turn on transistor O, and turn on the DC power supply! A negative gate current g is injected into the gate of GTO/. In other words, FIG. 2 shows a transient state during turn-off of the gate, in which carriers are taken out from the GTO/ space layer through the gate.

In FIG. 2, it is assumed that a gate current g is injected at time t0. Then, at time t2, GTO/ starts to turn off, and as the Anno-P current decreases, GTO/ starts to turn off.
The anode-to-A voltage (hereinafter referred to as anode voltage) of T,0/ starts to rise.With this rapid rise in anode voltage, the power loss of GTO/ also rapidly increases. begins to increase.

Next, at time t3, the value upstream of the anode enters the tail current section where the residual charge in the GTO flows out, and gradually decreases. This is due to the influence of the stray inductance of the distribution including /.On the other hand, GTO
The power loss P(・maximizes around time t3. This is caused by the sudden rise in the anode pressure due to the sudden decrease in the anode current.

When the maximum value of this power loss P exceeds the allowable value set for the GTO, local heat generation occurs in the element of the GTO, resulting in loss of voltage blocking ability (permanent deterioration). Therefore, commutation failure may occur, resulting in damage to the equipment.

Finally, at time t4, at the same time as the anode current becomes zero, the gate current ■8 also almost stops flowing, and the GT
Ono's turn-off is complete.

Now, in order to turn off the GT○/ safely and with as large an anode current as possible, it is necessary to prevent the power loss P at the time of turn-off from exceeding a permissible value. The most effective method is to suppress the power loss P (-vA x engineering A) by making the rise of the anno-1-' voltage ■□ gradual. Snubber circuits are added for this purpose.

Here, the snubber circuit is composed of a capacitor connected between the anode 1-''A of the GTO/ and the cathode (K), a diode 3, and a resistor circuit in parallel with this. In other words, the anode current When the voltage decreases and the anode voltage V begins to rise.

The voltage is absorbed through the series circuit of the capacitor and diode 3 (charging of the capacitor), thereby suppressing a sudden rise.

The charge stored in the capacitor λ is discharged through the resistor loop.

Now, in order to suppress the power loss at turn-off to an appropriate value, it is sufficient to increase the electrostatic capacity of the capacitor in the snubber circuit. Problems arise in that losses increase and efficiency decreases. This is because the loss caused by discharging the capacitor 2 is proportional to the capacitance of the capacitor and proportional to the switching frequency of the GTO/. For example, D.O.
IoV.

The loss of the snubber circuit when switching is performed using capacitors μF and uKH2 is as high as 'rtow.

[Purpose of the invention]

Therefore, one aspect of the present invention is to avoid reducing the efficiency in steady state (,
Another object of the present invention is to provide a snubber circuit for a self-extinguishing semiconductor element that cuts off as large a current as possible during overload (or overflow).

[Summary of the invention]

In order to achieve the above object, 1 the snubber i circuit according to the present invention includes a permanently installed snubber circuit that functions during steady operation, and a snubber i circuit that operates when the rate of increase in voltage between the anode and the cand exceeds a set value. The feature is that the second capacitor is inserted into the circuit.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 3 shows a first embodiment of the snubber circuit according to the present invention.

In FIG. 3, parts that overlap with those in FIG. 7 are given the same reference numerals, and their explanation will be omitted.

The circuit shown in FIG. 3 can be roughly divided into a main circuit including GTO/ and a gate extinguishing circuit 100 for G'l'O/.

a first snubber circuit 200 connected in parallel to GTO/;
The second snubber circuit 300 and the second snubber circuit 300 are connected in parallel to the second snubber circuit - 〇〇 during a transient period (failure).
It consists of a gate ignition circuit 00 for igniting the sirisk and the iris.

In the first snubber circuit 3θO, the first snubber circuit 3θO is connected in series with the thyristor hook as a switching element, and is parallel to the first snubber circuit θO as a whole (therefore, parallel to A− of GTO/ )It is connected to the. Resistor /3 and diode Y/s form a discharge circuit for first capacitor /2.

The gate ignition circuit aOθ connects the anode and can of GT○/.
The rate of change eLvA/ of the voltage V between 1 and 1 is detected by the capacitor ig and the resistor /q, and when avA/ exceeds the set value t, the Zener diode 20. Current flows through the resistor / to the pace of the transistor 〃, and when the transistor Ω is turned on, the resistance: 131/C flows through the transistor 〃.
? (7) When current flows through the pace, transistor/7 turns on, causing current to flow and turning on the Zyristor/G.

Next, the operation will be explained (see Fig. 9). The current of GT○/ is □, the voltage between anno-P and can-1 of GTO/ is 2, the rate of change of 6 is clVA, /a2. The on-off operation of the thyristorog is expressed as /g, and the respective waveforms are shown.

In FIG. 1, a indicates a case where the turn-off current of GTO/ is large, and b indicates a case where it is small.

First, when the turn-off current is small (1)), the voltage d1A/61 at the time of 2-turn off is also small, 4. Since the voltage is also small, the threshold voltage ve at A- is as shown by (bl).

Also, at this time, since A, /llt is also low due to the set value, Zener diode unit 0 does not conduct, and transistor /7. The second stays off. Therefore, thyristor/
ll even has an off trench. For this reason, only the first snubber circuit 200 of GT○/ is operated, and the snubber loss at this time is small.

Next, when the turn-off current of GTO/ becomes large as shown in (a), the current turn-off time of GT○/ is t2 to t3.
has the characteristic that it is hardly affected by the turn-off current air and remains almost constant. , hako. As it gets bigger, it gets bigger.

Therefore, the -voltage (2) rapidly increases as shown in (a) because the decreased current air charges the capacitor (2). Engineering. dVA7. when (a). , increases as shown in (a), and when it exceeds the set value K, current flows through the Zener diode shown in Figure 3, turning on transistor 2,
Then, transistor /7 is turned on to ignite Cyrisk /lI. When the thyristor /I is turned on, the capacitor /2 is connected as a snubber circuit, so that the voltage change can be significantly reduced as shown by the solid line.

In other words, the voltage increase rate dV is increased by turning on the thyristor hook.
Since A/, , is reduced, the turn-off loss P of GTO/ is also reduced. In this way, the load on turning off the GTO can be significantly reduced and a large current can be turned off.

Another embodiment of the invention is shown in FIG. In this example, G
The turn-off gate signal of TO/ is outputted in the polar direction G of the transformer 32 by turning on the transistor 3/ from the DC power supply 30 with the turn-off signal ■off, and the resistor 33 turns on the thyristor 3q to turn on the transistor 3/. A reverse current is applied to the gate of the thyristor to turn off the GTO/.Then, this turn-off signal is used by the transformer 3S as an on-signal power source for the thyristor/I. Since the configuration and operation are the same, the explanation will be omitted.

With this configuration, thyristor/eg G
Because it turns on only in synchronization with the turn-off signal of TO/,
The probability of malfunction of thyristor/l can be reduced,
This can contribute to improving reliability.

Note that if the GTO has a small capacity, the diode 3 may be omitted.

Further, even when a plurality of ()Tos are connected in series and used, by employing the above-mentioned configuration, it is possible to prevent deterioration of Vi due to imbalance in the voltage sharing of each GTO at the time of turn-off.

〔Effect of the invention〕

As described above, according to one aspect of the present invention, when the load is light, the nanocapacitor is operated with a smaller size, thereby reducing loss, thereby contributing to energy saving. On the other hand, in abnormal situations such as overload or overcurrent, the voltage change rate (rate of rise) of the voltage between the GTO's anode and cathode is detected, and if it exceeds the set value, the By adding a capacitor, the turn-off loss of the GTO can be significantly reduced, and a large current can be easily turned off.

[Brief explanation of the drawing]

FIG. 7 is a circuit diagram showing an example of a conventional four-sunner circuit, and FIG. 2 is a waveform diagram showing signal waveforms at various parts of the circuit of FIG. FIG. 3 is a circuit diagram showing an embodiment of the snubber circuit according to the present invention. FIG. 4 is a waveform diagram showing the 1g waveform of each part of the circuit of FIG. 3, and FIG. 5 is a circuit diagram showing another embodiment. 100...Gate arc extinguishing circuit, 20θ...1st snap circuit. 300...Ωth snubber circuit, +100...-gate ignition circuit, /...GT○1.2...1st capacitor, 3
...Diode-1I...Resistance, 7.2-...1st
Capacitor, /3...Resistor, //l...Zyristor,
/S...diode, /B, /9,. 2/. ,,! Mouth...Resistance, 7g...Capacitor, 20...
Zener diode, /7. M...transistor,
2'l, 3C1...DC power supply. 3.2, J5...Transformer. Applicant's agent Inomata Kiyosu 1 Diagram A Shimizu 2M tl ↑2↑314 Porridge 4 Diagram

Claims (1)

[Scope of Claims] In a snubber circuit in which a series circuit including a first capacitor and an impedance is connected between an anode and a cathode of a self-arc-extinguishing semiconductor element, A series circuit consisting of a second capacitor and a switching element connected to When the rate of increase in the voltage between the anode of the self-extinguishing semiconductor element and the capacitor P exceeds a set value, the switching
A control circuit that outputs a signal to close the element. A snubber circuit for a self-extinguishing semiconductor element, characterized by comprising: