JPS5989032A - Overvoltage preventing circuit of switching element - Google Patents

Abstract

PURPOSE:To prevent the breakdown of a switching element with no loss of energy by a absorbing temporarily the overvoltage by a capacitor and then restoring to a power supply from the capacitor. CONSTITUTION:A capacitor 46 is first charged up to a level equal to the voltage VS of a power supply 14. When a switching transistor TR20 is turned off, the overvoltage is applied to the TR20 and then absorbed by the capacitor 46 via a diode 42. Then the electric charge absorbed by the capacitor is restored to the power supply 14 via an inductance 48 when the terminal voltage of the capacitor 46 exceeds the voltage VS of the power supply 14. Thus useless discharge is avoided by the polarity of the diode 42.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an overvoltage prevention circuit for a switching element, and particularly to an overvoltage prevention circuit for a switching element provided at both ends of the switching element.

Prior art Do to control load equipment by controlling direct current
The Chotsunozo device is well known, and Figure 1 shows the conventional DC
The Chotsuno ξ device is shown.

In FIG. 1, the input terminal 12 of the DC chopper device 10
A power supply 14 is connected to a and 12b, a motor 18 is connected as a load device to output terminals 16a and 16b of the DC chopper device 10, and the current from the power supply 14 to the motor 18 is controlled by the DO chopper device 10. That will happen.

Next, the configuration of the dot transfer device 10 will be explained in detail.

The DC chopper device 10 is provided with, for example, a transistor 20 as a switching element for controlling the current from the power source 14, and the collector terminal of the transistor 2o is connected to the motor 18 via the output terminal 16b.
The emitter terminal of o is connected to the power supply 14 via the input terminal 12b. A base drive circuit 22 is connected to the pace terminal of the transistor 2o, and the pace current from the base drive circuit 22 performs the switching operation of the transistor 2°, thereby controlling the current from the power supply 14 and [the motor 18 controlled. Further, a reverse voltage prevention diode 24 is connected between the collector and emitter of the transistor 20, and the diode 24 can prevent a reverse voltage from being applied to the transistor 2°. Furthermore, both ends of the motor 18 (output terminal 16a
A flywheel diode 26 is connected to 116b), and when the transistor 20 is turned off, the nuclear flywheel diode 26 operates to conduct current to the motor 18. In addition, in FIG. 1, 28, 30, and 32 indicate wiring inductance.

FIG. 2 shows voltage waveforms for explaining the action of the Do chopper device 1o in FIG. The voltage VeC is shown.

Before time t1, the pace current is not supplied from the base drive circuit 22 and the pace voltage VBB is 0, so the transistor 2o is in an off state, and the emitter-collector voltage VeC is equal to the voltage VB of the power supply 14. .

Time 1. When a pace current is supplied from the base drive circuit 22 to the pace of the transistor 2o, the pace voltage VIIB becomes V. equal to n, transistor 2
0 is on operation, emitter-collector voltage VeC is O
(Actually, it will be several Zelts).

At time t, when the base drive circuit 22 stops supplying the pace current, the pace voltage VBB becomes 0, the transistor 20 is turned off, and the emitter-collector voltage vec becomes Vn.

When the transistor 20 is turned off at time t, there is a problem in that an overvoltage (2) occurs.

This overvoltage vs is the wiring inductance of 28.30.
A flywheel diode 26 is connected in parallel to the inductance L, the current flowing through the transistor 20, and the motor 18, and the flywheel diode 26 causes an overvoltage (2) to the motor 18.

The shadows have been removed.

Due to this overvoltage vs, the emitter-collector voltage VeC of the transistor 20 becomes V, . . . +V, and if the emitter-collector voltage VeC exceeds the withstand voltage of the transistor 20, there is a problem that the transistor 20 is destroyed. Therefore, conventionally, an overvoltage prevention circuit was provided at both ends of a switching element such as a transistor, and the overvoltage prevention circuit lowered the overvoltage 5, thereby preventing destruction of the switching element.

FIG. 3 shows a conventional overvoltage protection circuit, which is similar to the circuit of FIG.

In FIG. 3, the overvoltage protection circuit includes transistor 2o
It consists of a resistor 34 and a capacitor 36 connected in series between the emitter and the converter, and the resistor 34 and capacitor 36
As a result, overvoltage v5 is absorbed. Note that the resistance value of the resistor 34 and the capacitance of the capacitor 36 are set to values that allow the emitter-collector voltage VeC to operate without oscillating. However, in the overvoltage prevention circuit shown in FIG. 3, when the capacitance of the capacitor 36 is set large and the resistance value of the resistor 34 is set small in order to reduce the overvoltage (8), there is a problem in that energy loss increases. .

That is, when the transistor 20 is turned off,
When the capacitor 36 is charged with an overvoltage VB and the transistor 20 is turned on, the electric charge charged in the capacitor 36 is discharged by the resistor 34, transistor 20, and capacitor 360 circuit, which increases energy loss. , there was a problem.

FIG. 4 shows another conventional overvoltage prevention circuit.

In FIG. 4, a diode 38 is connected in parallel with the resistor 34, and when the transistor 20 is turned off, the overvoltage (2) is applied to the capacitor 3 via the diode 38.
6 and the transistor 20 is turned on, the charge stored in the capacitor 36 is discharged through the resistor 34.

Therefore, by appropriately setting the resistance value of the resistor 34, the energy loss can be reduced compared to the overvoltage prevention circuit shown in FIG. 3, but there is still a problem that loss still occurs.

As described above, the conventional overvoltage prevention circuit has the problem of increased energy loss.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide a breakdown voltage prevention circuit for switching elements that reduces overvoltage without increasing energy loss.

Structure of the Invention In order to achieve the above object, the present invention provides an overvoltage prevention circuit for a switching element provided at both ends of a switching element, in which a diode for backflow prevention and an overvoltage absorption circuit are connected in series at both ends of the switching element. A capacitor is provided, both ends of the capacitor are connected to a power supply, and when an overvoltage is applied to the switching element, the overvoltage is absorbed by the capacitor via the diode, and after the overvoltage disappears, the charge absorbed by the capacitor is is characterized by being reduced to a power source.

Embodiments Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 5 shows a first principle explanatory diagram of the invention.

In FIG. 5, a diode 42 and an auxiliary power supply 44 are connected in series between the emitter and collector of the transistor 20, and the voltage of the auxiliary power supply 44 is equal to the voltage vB of the power supply 14.
, and the impedance of the auxiliary power supply 44 is set to be extremely small.

When the transistor 20 is turned off, the overvoltage v8 is absorbed by the auxiliary power supply 44 via the diode 42, so a voltage higher than Vn is not applied to the transistor 20, and the transistor 20 can be prevented from being destroyed. Furthermore, since the diode 42 is provided after the overvoltage (3) disappears, the charge absorbed by the auxiliary power source 44 will not be discharged, and energy loss can be prevented.

FIG. 6 shows a second principle explanatory diagram of the present invention.

In FIG. 6, instead of the auxiliary power source 440 in FIG.
A capacitor 46 is used, and the positive terminal Bc of the capacitor 46 is connected to the positive terminal of the power supply 14, and the capacitor 46 has a large capacity to provide low impedance. And transistor 20
When the is turned off, the overvoltage v5 is absorbed by the capacitor 46 due to the same effect as shown in the principle explanatory diagram of FIG.
After the overvoltage 5 disappears, the charge absorbed by the capacitor 46 is returned to the power supply 14 via the positive terminal Bc.

Therefore, the energy of the overvoltage V can be returned to the power supply 14.

FIRST EMBODIMENT FIG. 7 shows the state force when the overvoltage protection circuit according to the first embodiment of the present invention is applied to a DC chopper device.
The principle of the figure is applied to the device (FIG. 1).

A characteristic feature of the present invention is that a diode for preventing backflow and a capacitor for absorbing overvoltage are connected in series at both ends of the switching element, and both ends of the capacitor are connected to a power supply. - In the first embodiment, a diode R42 for preventing reverse current and a capacitor 46 for absorbing overvoltage are connected in series between the emitter and collector of the transistor 20', and the positive terminal of the capacitor 46 is connected to the input terminal. It is connected to the positive side terminal of the power supply 14 via the terminal 12a. Furthermore, an inductance 48 is provided between the positive side terminal of the capacitor 46 and the input terminal 12a, and the inductance 48 causes the diode 42 to The current flowing through the flywheel diode 26 and the current flowing through the flywheel diode 26 can be !1liil,I!.Furthermore, the resistor 34 and capacitor 36 connected in series between the emitter and collector of the transistor 2o are connected to the emitter-collector voltage VeC. The resistor 34 and capacitor 36 can also be omitted.

The first embodiment of the present invention consists of the above description, and its operation will be explained below.

First, in the initial state, the current of the power supply 14 is supplied to the capacitor 46 via the inductance 48, and the capacitor 46 is charged, so that the voltage of the capacitor 46 is equal to the voltage 6 of the power supply 14 (1-()). There is.

Next, when the transistor 2o is turned on, the overvoltage V8 of the transistor 20Vc is applied, and the overvoltage V8
is supplied to the capacitor 46 via Mayo P42 and absorbed by the capacitor -+j46.

After that, when the voltage of the capacitor 46 becomes higher than the voltage 8 of the power supply 14, the charge absorbed by the capacitor 46 is returned to the power supply 14 via the inductance 48, so that the voltage of the capacitor 46 becomes higher than the voltage of the power supply 14. It becomes equal to the voltage vB of . Therefore, since the overvoltage 5 is absorbed by the capacitor 46, a voltage higher than VB is not applied to the transistor 2o, and furthermore, the energy of the overvoltage V8 can be returned to the power supply 14 without being consumed. Therefore, no energy loss occurs.

Since the charge absorbed by the capacitor 46 is not discharged due to the polarity of the diode 42, no loss occurs. Therefore, it is possible to set the capacitance of the capacitor 46 sufficiently large and further reduce the impedance.

As described above, according to the first embodiment of the present invention, the overvoltage (5) can be absorbed by the capacitor 46, so that a voltage higher than vB is not applied to the transistor 20, and the transistor 20 is destroyed. Furthermore, since the charge absorbed by the capacitor 46 is returned to the power supply 14, no energy loss occurs.

In addition, FIG. 8 shows the relationship between time and emitter-collector voltage, and FIG. 8 (,) is a graph of the conventional circuit of FIG. 1, and FIG. 3 is a graph of the first embodiment circuit shown in FIG. Here, the current of −E−18 is 4
00(A), and in FIG. 8(b), capacitor 4
6 is 4000 μF. 8(a) and 8.
As is clear from the comparison with Figure (b), it is understood that the overvoltage V8 is reduced in the first embodiment.

In addition, in FIG. 7 above, from the capacitor 46 to the power supply 1
An inductance 48 is provided in the reduction system to 4. As described above, this inductance 48 is connected to the current flowing through the flywheel diode 26 and the diode 4).
42 and the current flowing through it.

That is, when the transistor 20 is off, the current flowing to the motor 18 passes through the diode 26, the current due to the overvoltage 8 of the transistor 20 passes through the diode P42, and the current flowing through the diode 26 passes through the diode P42.
This prevents the relatively small capacitance diode 42 from being destroyed by flowing into the circuit 42. In other words, each diode F'2
Since both of the currents flowing through 6.42 have relatively high frequency components, they are separated by the inductance 48 so as not to interfere with each other. Note that it is also possible to set the inductance 48 to 0, and in this case, the positive terminal of the capacitor 46 is directly connected to the positive terminal of the power supply 14.

Second Embodiment Next, FIG. 9 shows a state in which an overvoltage prevention circuit according to a second embodiment of the present invention is applied to a Do chopper device.

In the second embodiment, the flywheel diode F″2
6 is also used as the diode F'42 for preventing backflow, and the second embodiment can also achieve the same effect as the first embodiment. That is, when the transistor 20 is turned off, the overvoltage 8 is supplied to the capacitor 46 via the flywheel diode 26 and absorbed by the capacitor 46, and after the overvoltage vs disappears, the charge absorbed by the capacitor 46 is transferred to the power supply. This will be reduced to 14.

Therefore, according to the second embodiment as well, overvoltage can be reduced without increasing energy loss, and destruction of the transistor 20 can be prevented.

Note that in the first and second embodiments described above, a transistor is used as a switching element, but a thyristor or a GTO (gate turn-off thyristor) may also be used.

Furthermore, in the first and second embodiments described above, the overvoltage prevention circuit of the present invention is applied to a DC chopper device, but the overvoltage prevention circuit of the present invention can also be applied to other devices, for example, an innovative device. It is.

As described in detail, according to the present invention, when an overvoltage is applied to a switching element, the overvoltage is absorbed into a capacitor via a diode, so that destruction of the switching element can be prevented, and the overvoltage can be prevented. After being dissipated, the charge absorbed by the capacitor is returned to the power source, so no energy loss occurs. Therefore, it is possible to reduce overvoltage without increasing loss and prevent destruction of the switching element. Further, since the overvoltage absorbing capacitor is unrelated to loss, its capacitance can be set sufficiently large.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional DC chopper device, Fig. 2 is a voltage waveform diagram for explaining the operation of the DC chopper device of Fig. 1, Fig. 3 is a circuit diagram of a conventional overvoltage prevention circuit, and Fig. 4 is a circuit diagram of a conventional overvoltage prevention circuit. A circuit diagram of another conventional overvoltage prevention circuit, FIG. 5, is the first circuit diagram of the present invention.
FIG. 6 is a diagram explaining the second principle of the present invention, and FIG. 7 is a diagram explaining the principle of the overvoltage prevention circuit according to the first embodiment of the present invention.
o A circuit diagram showing a state applied to a chopper device, Fig. 8 is a graph showing the relationship between time and emitter-collection voltage, and Fig. 9 shows an overvoltage prevention circuit according to a second embodiment of the present invention.
FIG. 2 is a circuit diagram showing a state in which the present invention is applied to an o chopper device. 14... Power supply, 20... Transistor, 26... Flywheel diode, 42... Diode, 46... Capacitor, 48... Inductance. Agent Patent Attorney Yoshi 1) Kenji (1 other person) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 [- 1 [- -

Claims (1)

[Claims] (1) In an overvoltage prevention circuit for a switching element provided at both ends of the switching element, a diode P for backflow prevention connected in series is provided at both ends of the switching element.
A capacitor for absorbing overvoltage is provided, both ends of which are connected to a power supply, and when an overvoltage is applied to the switching element, the overvoltage is absorbed by the capacitor via the diode, and after the overvoltage disappears, it is absorbed by the capacitor. An overvoltage prevention circuit for a switching element, characterized in that the generated charge is returned to a power source. (2. Scope of Claims (1) In the circuit described in claim (1), an overvoltage prevention circuit for a switching element is characterized in that an inductance is provided in the reduction system from the capacitor to the power source. (3) Scope of Claims In the circuit described in (1) or (2), the load device controlled by the switching element is provided with a flywheel diode, and the overvoltage of the switching element is characterized in that the flywheel diode is also used as the backflow prevention diode. prevention circuit.