JPS63167520A - Snubber circuit for semiconductor switch element - Google Patents

Abstract

PURPOSE:To decrease the turn-on loss by connecting a saturable reactor to a discharge line of a capacitor being a component of a snubber circuit so as to slow down the leading of a discharge current when a semiconductor switch element is turned on. CONSTITUTION:A saturable reactor 5 is connected in series with a resistor 4 of the snubber circuit. The saturable reactor is not subjected to magnetic saturation at the leading of a discharge current (i) of the capacitor 3 but acts like an inductance and its magnetism is saturated after a terminal voltage Vak of a thyristor 1 is sufficiently decreased. Thus, when the thyristor 1 is turned on, the leading of the discharge current of the capacitor 3 slows down and the switching loss is decreased. While the reactor 5 is saturated, the discharge current of the capacitor 3 flows with the same timewise gradient as that of a conventional circuit and the thyristor 1 is protected at the turn-off by the same operation as that of a conventional snubber circuit after the discharge of the capacitor 3 is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a snubber circuit for a semiconductor switch element that reduces turn-on loss of the semiconductor switch element.

(Prior Art) Conventionally, as a snubber circuit for a semiconductor switching element such as a thyristor, a series circuit of a diode 22 and a capacitor 23 is connected in parallel to a thyristor 21, as shown in FIG. It is known that a resistor 24 is connected in parallel to the resistor.

To explain the function of this snubber circuit, first, the thyristor 2
1, when a trigger is applied to the gate of thyristor 21, thyristor 21 is turned on and the electric charge that had been charged in capacitor 23 is discharged through resistor 24, as shown in FIG. A discharge current i' as shown in FIG.

FIG. 6 shows the terminal voltage Vak of the thyristor 21 at this time.

Discharge current i' and power loss at turn-on (Vak×
i'), and the capacitor 23 must quickly finish discharging to prepare for the excessive voltage applied when the thyristor 21 is turned off.

(Problem to be Solved by the Invention) Here, in order to speed up the discharge of the capacitor 23, the value of the resistor 24 can be reduced, but if this is done, di'/dt at the rise of the discharge current i' becomes large. ,
The turn-on loss (VakXi') increases, and since the current is concentrated near the gate of the thyristor 21 when the thyristor 21 is turned on, the capacitor 2
If the discharge of 3 is too fast, there is a problem that the thyristor 21 will be destroyed due to concentration of current in a short period of time.

The present invention was proposed to solve the above-mentioned problems, and its purpose is to reduce the turn-on loss of semiconductor switching elements such as thyristors, and to ensure an appropriate discharge time of the capacitor, thereby improving the performance of semiconductor switching elements. An object of the present invention is to provide a snubber circuit which prevents damage to the snubber circuit.

(Means for Solving the Problems) In order to achieve the above object, the present invention connects a series circuit of a diode and a capacitor in parallel to a semiconductor switch element, and connects a resistor in parallel to the diode. It is characterized by connecting a series circuit with a saturable reactor.

(Function) In the present invention, the saturable reactor connected in series with the resistor of the snubber circuit slows down the rise of the att current of the capacitor when the semiconductor switch element is turned on, reducing switching loss. While the saturable reactor is saturated.

The discharge current of the capacitor flows at the same slope as before.

After the discharge of the capacitor is completed, the semiconductor switch element is protected at turn-off by a function similar to that of a conventional snubber circuit.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a thyristor as a semiconductor switching element, and a series circuit of a diode 2 and a capacitor 3 is connected in parallel to the thyristor 1.

Here, the polarity of the diode 2 is such that the capacitor 3 is charged when the thyristor 1 is non-conducting. Also,
A series circuit consisting of a resistor 4 and a saturable reactor 5 is connected in parallel to the diode 2.

To explain this operation, when the thyristor 1 is turned on, the charge that had been charged in the capacitor 3 is discharged through the series circuit of the resistor 4 and the saturable reactor 5. At this time, the saturable reactor 5 is assumed to have saturation magnetization characteristics as shown in FIG. Choose one that will become magnetically saturated after the temperature drops sufficiently.

In FIG. 2, Φm represents the saturation magnetic flux, and is represents the current required to saturate the saturable reactor 5.

With this configuration, as shown in FIG. 3, in the time tS until the saturable reactor 5 is saturated,
The discharge current i rises slowly due to the saturable reactor 5 acting as an inductance.Next, when the saturable reactor 5 becomes magnetically saturated, the discharge current i (i≧is) is not affected by the saturable reactor 5 and only the resistor 4 The discharge current i increases at the same slope as the conventional discharge current 11 while being limited by However, it is slowly decreasing.

In addition, in FIG. 3, tr is a schematic rise time of the thyristor 1 - (VakX i') is the turn-on loss due to the discharge current i' of the circuit of FIG. 5, and according to this embodiment, the rise time tr Since the discharge current i rises slowly, the turn-on loss (VakXi) is significantly reduced compared to the conventional case.

Furthermore, in the conventional example shown in FIG. 5, the value of the resistor 4 cannot be made small for the reason mentioned above, but in the present invention, the value of the thyristor 1 cannot be reduced at the rise time ts of the charging current i.
Since the turn-on region of , the subsequent rate of change di/dt of the current can be made larger than the value allowed immediately after turn-on. Therefore, there is no problem even if the value of the resistor 4 is made smaller than in the conventional case, and the disadvantage that the discharging time of the capacitor 3 becomes longer than in the conventional case can be solved as described below.

That is, FIG. 4 shows thyristor 1. Various characteristics are shown when the diode 2, capacitor 3, and saturable reactor 5 have the same characteristics as in FIG. 1, and only the value of the resistor 4 is reduced. As is clear from this figure, by reducing the resistance 4, the increase in the discharge current i after the saturable reactor 5 is saturated becomes steeper, making it possible to discharge the capacitor 3 in approximately the same time as before. Become.

Furthermore, the discharge time can be further shortened by selecting the value of the resistor 4.

In the above embodiments, the case where a thyristor (SCR) was used as the semiconductor switching element was explained, but it goes without saying that it can also be applied to a transistor. In this case, the present invention is particularly effective because a relatively large capacity capacitor is used in the snubber circuit and the discharge current i becomes large.

(Effects of the Invention) As detailed above, according to the present invention, since the saturable reactor is connected to the discharge path of the capacitor constituting the snubber circuit, the rise of the discharge current when the semiconductor switch element is turned on is slowed down. can reduce turn-on loss.

Further, even when the resistance value of the snubber circuit is reduced to shorten the discharging time of the capacitor, there is an effect that there is no risk of destroying the semiconductor switch element when it is turned on.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a characteristic diagram of a saturable reactor, Figs. 3 and 4 are waveform diagrams for explaining the operation, and Fig. 5 is a conventional example. The circuit diagram shown in FIG. 6 is a waveform diagram for explaining the operation. 1... Thyristor 2... Diode 3
... Capacitor 4 ... Resistor 5 ... Saturable reactor Ml Figure M2 Figure 5 Figure Zum Figure 6

Claims (1)

[Claims] A snubber circuit for a semiconductor switch element, characterized in that a series circuit of a diode and a capacitor is connected in parallel to the semiconductor switch element, and a series circuit of a resistor and a saturable reactor is connected in parallel to the diode. .