JPH02194726A - Snubber circuit for high speed switching element - Google Patents

Abstract

PURPOSE:To suppress the transient overvoltage of a fly-wheel diode at the time of restoring an inverse characteristic and to allow the withstand voltage selection of a diode to be appropriate by installing the diode generating a bypass line for discharging accumulated energy in a wiring inductance on the output side of a switching element. CONSTITUTION:The diode Dn2 is provided between the fly-wheel diode Dw and a snubber capacitor Cn. When the transient voltage of the diode Dw corresponding to the ON-operation of te switching element 2 at the time of restoring the inverse characteristic is superposed on a DC power voltage Ed and inversely impressed on the diode Dw, a charge current Isn with respect to the capacitor Cn is conducted in correspondence with the difference voltage of the superimposed voltage and the normal terminal voltage of the capacitor Cn. Then, the accumulated energy of a wiring inductance 4 part is discharged. Thus, the abnormal rise of transient backward electromotive force is controlled and the enhancing the withstand voltage of the fly-wheel diode is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a snubber circuit for a high-speed switching element in a switching power supply device, an inverter device, or the like.

[Conventional technology]

As a conventional snubber circuit for this type of switching element, there is known a chopper circuit shown in FIG. 5 as an example.

In Fig. 5, 1 has a DC power supply with a voltage E4, 2 has a diode D connected in antiparallel, and has a voltage of 0 at a predetermined frequency.
a switching element such as a transistor that is N-OFF controlled to connect and disconnect the DC voltage E; 3 is a wiring inductance with a value 1; 4 is a wiring inductance R with a value 12 inside or near the switching element 2;
, , and Dl and 07 are the switching elements 2, respectively.
A resistor, a diode, and a capacitor form a snubber circuit, DCL and Cf are a DC reactor and a capacitor for filtering the intermittent DC output of the switching element 2, respectively, and D is the filtered DC output voltage. . is a flywheel diode for recycling the stored energy of an inductive load. Note that 71w is the voltage across the switching element 2, rsw is the passing current of the inductance 4, 1, i is the passing current of the reactor DCL,
v7 and ■. are the voltage across the flywheel diode Dw and the passing current, respectively.

[Problem to be solved by the invention]

However, in the conventional snubber circuit as described above, when the switching element is a transistor and its type is changed from a bipolar type to a field effect type, for example, to speed up its operation time, the turn-on time is reduced. At the same time, the time rate of change of the current flowing when the switch is turned on becomes large, and the transient voltage generated by the wiring inductance 12 as described above also becomes large. Therefore, the sum of the transient voltage and the DC power supply voltage is calculated as There was a risk that the flywheel diode, which was subjected to a reversely applied voltage, would suffer voltage damage.

FIG. 6 is an operational waveform diagram of the specifications of each part of the circuit shown in FIG. 5, showing the above relationship. Note that in the figures, except for figure (A), the solid line and the dashed-dotted line correspond to the case of a field effect transistor and a bipolar transistor, respectively.

FIG. 6(a) shows the ON (closed circuit) and OFF (open circuit) states of the switching element 2. FIG. 6(d) shows a variation pattern of the current 1fw flowing through the flywheel diode D, and the phenomenon of reversal of the current flowing direction as shown in the figure of the current (1) occurs when the flywheel diode D is applied with a voltage in the reverse direction due to the ON operation of the switching element. Diode D. This is due to the discharge of accumulated charge of minority carriers, and indicates the reverse recovery characteristics of the diode. FIG. 6(C) shows the passing current I□ of the switching element 2, which is determined in relation to the turn-on time characteristic of the element, the overall time constant of the current flow path of the current Lw, and the reverse recovery characteristic of the diode Dw. be done. Figure 6 (
B) shows the composite current (1) of the two currents 1gw and Ifw. FIG. 6(E) shows the flywheel diode D. When the current 1 sw decreases, the transient back electromotive force Δ■ generated in the inductance 4 in a direction that prevents the decrease is superimposed on the DC power supply voltage Ea. .

As shown in FIGS. 6(B) to 6(E), the current 1
sw and ■1 and voltage v1. Regarding, in the case of the field effect transistor shown by the solid line in the figure, compared to the case of the bipolar transistor which has a longer turn-on time shown by the dashed-dotted line, I□□〉I□ at each maximum value.
1. ■□II〉If, *t+ΔV□, >ΔV□2, all of which become large. Therefore, in order to increase the speed of the switching element as described above, it is also necessary to strengthen the withstand voltage of the flywheel diode as described above.

In view of the above, an object of the present invention is to provide a snubber circuit for a high-speed switching element that suppresses the abnormal increase in the transient back electromotive force ΔV0 and eliminates the need to strengthen the breakdown voltage of the flywheel diode.

[Means to solve the problem]

In order to achieve the above object, the snubber circuit for a high-speed switching element of the present invention connects in series a high-speed switching element having a diode connected in anti-parallel and a diode connected in anti-parallel to its inductive load. A snubber circuit for the high-speed switching element of a DC intermittent circuit consisting of a series-parallel circuit consisting of a capacitor connected in series with a parallel connection of a diode and a resistor in the forward direction with respect to the DC power supply voltage. In the snubber circuit of the high-speed switching element connected in parallel to the DC intermittent circuit, the above-mentioned At the time of reverse recovery of the load parallel diode, the current passing through the high-speed switching element suddenly decreases, and the polarity causes a charging current to flow to the capacitor due to a transient voltage generated based on wiring inductance inside or near the high-speed switching element. It is equipped with an inserted diode.

[Effect]

O of the switching element 2 in the connection as shown in FIG.
The conduction current 1 tw during the N operation becomes a short-circuit current to the DC power supply 1 due to the discharge of the minority carrier charge of the flywheel diode Dw in the reverse characteristic recovery process of the flywheel diode Dw due to the ON operation, and increases transiently. It reaches a steady value when the discharge ends. At this time, the current 1. The time rate of change of □ is the sum of wiring inductances 3 (value 1.) and 4 (value 12), which is the total inductance in the current carrying path, and the closing operation time (turn-on time) Ton of the switching element 2. The time T is determined as the main factor. It increases as H becomes shorter, that is, the speed of the switching element increases.

In the decreasing period of the current 1sw immediately before the reverse characteristic recovery corresponding to the end of charge discharge of the diode D8,
The current 1 sw in the wiring inductance 4 parts
Transient back electromotive force ΔV m generated in a direction that prevents the decrease of
u is superimposed on the voltage E4 of the DC power supply 1, which is a steady reverse voltage to the diode Dw, and the combined value may exceed the specified reverse breakdown voltage value of the diode depending on the value of the transient voltage ΔVS. obtain.

Therefore, the present invention aims to suppress the transient voltage Δv0 by providing a discharge path forming diode that bypasses the release of the stored energy in the wiring inductance 4, which appears as the transient voltage Δv, to the snubber capacitors C and l. It is. By forming the bypass path as described above, the transient voltage Δ■ becomes as shown in the following equations (1) and (2).

−・・−−1−−−・・・・−・・ (1) However, Lwp is the peak value of the current Isw, VD is the engraved layer pressure of the bypass path diode, and C, is the snubber It is the capacitance of a capacitor.

〔Example〕

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

Fig. 1 is a circuit diagram showing an embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
The operating waveform diagrams of the answer section specifications, FIG. 3 and FIG. 4 are respectively a circuit diagram of a PAM type inverter device and a PWM type inverter device using the snubber circuit according to the present invention.

In FIG. 1, components having the same functions as in the prior art embodiment shown in FIG. 5 are given the same reference numerals.

Figure 1 shows the flywheel diode D in Figure 5.
. A diode D1 is provided between the snubber capacitor C7 and the snubber capacitor C7 with the polarity shown. Therefore, when the transient voltage Δv0 at the time of recovery of the reverse characteristic of the diode D corresponding to the ON operation of the switching element 2 is superimposed on the DC power supply voltage E4 and reversely applied to the diode D, the superimposed voltage and the capacitor A charging current ■□ is applied to the capacitor in accordance with the voltage difference from the steady terminal voltage of C7, thereby discharging the energy stored in the wiring inductance 4 and suppressing the transient voltage Δvfi.

FIG. 2 shows each of the above-mentioned operating states, and corresponds to the operating waveform diagram of FIG. 6 in the case of the prior art. The transient voltage Δv spl shown in FIG. 6(e) is suppressed as shown by Δvo in FIG. 2(e) even when a high-speed switching element is used. As shown in FIG. 2(f), the capacitor charging current Is'n becomes pulsed and has a peak value of 1.
7. has.

FIG. 3 is a circuit diagram of a PAM type inverter device having a diode D1 according to the present invention, 2a is a field effect transistor as a high-speed switching element, 5 is a rectifier,
6 is an inverter, 7 is an AC motor, and Cf is a filtering capacitor.

FIG. 4 shows, similarly to FIG. 3, a diode Dfi according to the invention.
FIG. 2 is a circuit diagram of a three-phase PWM inverter device having inverter units 6u+6v+6w+ for each of the three phases U, V, and W. Note that the diodes DsI and I)@t function as flywheel diodes corresponding to the field effect transistors 2° and 2°1, respectively.

〔Effect of the invention〕

According to the present invention, a DC voltage intermittent circuit is constructed of a high-speed switching element for varying the DC supply voltage of an inductive load with flywheel diodes in antiparallel, and a snubber circuit consisting of a series-parallel circuit of a resistor, a diode, and a capacitor. In the circuit, a diode is provided between the flywheel diode and the snubber circuit capacitor to form a bypass path for discharging the stored energy in the wiring inductance on the output side of the switching element. Transient overvoltage can be suppressed, and the withstand voltage of the diode can be appropriately selected.

[Brief explanation of the drawing]

FIG. 1 is a chopper circuit diagram using a snubber circuit according to an embodiment of the present invention, FIG. 2 is an operating waveform diagram of the specifications of each part of the circuit shown in FIG. 5 is a chopper circuit diagram using a snubber circuit according to the prior art, and FIG. 6 is an operating waveform diagram of specifications of each part of the circuit shown in FIG. 5. 1... DC power supply, 2.2-. 2u+, 2uz... Switching element, 3, 4... Wiring inductance, 5
... Rectifier, 6.6. ．． 6v, 6. ...Inverter, 7...AC motor, Cfl+Cf2. CB+
C+r++ Cn□・・・Codenser, D 111
-D114+ Dal Dst+ Dst, D
w...Diode, DCL...DC reactor, R
111R RRt...Resistance. Figure 1 Figure 2 Figure 2 Figure SW Hai Figure

Claims (1)

[Claims] 1) A snubber circuit for the high-speed switching element of a DC intermittent circuit formed by connecting in series a high-speed switching element having a diode connected in anti-parallel and a diode connected in anti-parallel to its inductive load, the snubber circuit for the high-speed switching element; A snubber of the high-speed switching element is connected in parallel to the DC intermittent circuit, forming a series-parallel circuit consisting of a capacitor connected in series with a parallel connection of a diode and a resistor in the forward direction with respect to the power supply voltage. In the circuit, between the connection point between the diode and the capacitor of the snubber circuit and the output side or input side terminal of the high-speed switching element,
polarity that causes a charging current to flow through the capacitor due to a transient overvoltage generated based on wiring inductance inside or near the high-speed switching element as the current flowing through the high-speed switching element suddenly decreases during reverse recovery of the load parallel diode; A snubber circuit for a high-speed switching element characterized by having a diode inserted in the circuit.