JPH0354913A - Transistor driving circuit - Google Patents

Abstract

PURPOSE:To shorten the turning-off time of transistors(TRs) and to eliminate the need for a TR with large reverse dielectric strength by connecting a circuit for clipping reverse voltage between the base and emitter of the TR at the time of turning off the TR. CONSTITUTION:In order to shorten the turning-off time of the TRs 2, 3, a large reverse voltage is impressed between the bases and emitters of the TRs 2, 3. Diodes 13, 14 are connected in parallel with resistors 13, 14 in the forward direction against the revese voltage of the TRs 2, 3. A small signal TR 16 is connected between the base and emitters of the TR 3 so as to control the ON/OFF of the TR 3 and vary its output. The ON/OFF period of the TR 16 is controlled by a control circuit 17. A constant voltage diode 18 and a diode 19 are connected in series between the base and emitter of the TR 3.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a transistor drive circuit.

(Prior art) For example, in a transistor used as a power switch, in order to reduce heat generation during turn-off, a reverse voltage is applied between the base and emitter of the transistor to speed up turn-off. ，Already well known.

FIG. 2 shows the waveform of the voltage applied between the base and emitter, where A is the reverse voltage. During the time t from when this reverse voltage is applied until it reaches a predetermined negative voltage, collector current continues to flow through the transistor, and switching loss at this time is the main cause of heat generation in the transistor. .

In order to reduce this heat generation, it is necessary to shorten this time t. Therefore, a large reverse voltage B as shown by the dotted line
If the voltage is applied, the time for the voltage to drop to the predetermined voltage is t', which is shorter than the time t. By the way, regarding this type of transistor. It may be required that the output be variable. To do this, it is sufficient to adjust the on/off time of the transistor. To do this, another transistor may be connected between the base and emitter of this transistor, and the on/off time of this transistor may be controlled.

(Problems to be Solved by the Invention) However, when using such a control transistor, there are the following problems. In other words, as described above, a reverse voltage is applied between the base and emitter of the transistor to be controlled, such as a power transistor, to increase the turn-off speed. It also has a large capacity to withstand current flowing due to reverse breakdown voltage.

Therefore, if a small-signal transistor is used as a control transistor to make it smaller and cheaper, such a small-signal transistor has a small reverse breakdown voltage, and when current flows due to the reverse breakdown voltage, the characteristics deteriorate. There are things to do.

Conventionally, therefore, the reverse voltage of the transistor to be controlled is reduced, the switching loss is large, and the heat generated by the transistor is radiated using a heat radiating means.
Alternatively, control transistors with high reverse breakdown voltage characteristics were used.

However, all of these methods involve increasing the size of the equipment and have drawbacks such as rising manufacturing costs.

The purpose of this invention is to make it possible to use a small signal transistor as a control transistor even when a large reverse voltage is applied, in order to shorten the turn-off time of the transistor. (Means for Solving the Problems) The present invention provides a configuration in which a small signal transistor for controlling on/off of the transistor to be controlled is connected between the base and emitter of the transistor to be controlled, Sometimes, a series circuit of a constant voltage diode and a diode for clipping a reverse voltage applied between the base and emitter is connected between the base and emitter of the transistor to be controlled.

(Function) There is a series circuit of a constant voltage diode and a diode to clip the reverse voltage applied between the base and emitter of the transistor, so a voltage higher than the clip voltage is not applied to the small signal transistor. become.

Therefore, there is no need to use a transistor with a high reverse breakdown voltage as a small signal transistor.

On the other hand, it becomes possible to apply a reverse voltage with a large slope between the base and emitter of the transistor to be controlled, thus shortening the time until turn-off. (Example) An example of the present invention will be described with reference to the drawings. The figure shows an example in which the present invention is applied to drive a transistor used in an oscillation circuit for lighting in a discharge lamp lighting device, in which 1 is a DC power supply, 2 and 3 are transistors that are turned on and off alternately, 4, 5 is a capacitor and reactor forming a resonant circuit, and 6 is a discharge lamp.

When the DC power supply is turned on, a pulse is sent from the starting circuit 7 to the base of the transistor 3, thereby turning on the transistor 3. As a result, a resonant current flows through the DC cut capacitor 8, capacitor 4, and reactor 5. Thereafter, the transistors 2 and 3 are alternately turned on and off by the vibrations of the capacitor 4 and reactor 5 and the drive transformer 9. That is, a secondary coil 11.12 is connected to the primary coil 10 of the driving transformer 9 connected in series with the reactor 5 via a resistor 13.14 between the base and emitter of each transistor 2, 3. The transistors 2 and 3 are alternately turned on and off by the voltages of the secondary coils 1↓ and 12, respectively.

At this time, the voltage of the capacitor 4 is applied to the discharge lamp 6, and the discharge lamp 6 is thereby turned on.After the lamp is turned on, the resonance loop changes from the initial capacitor 4 to a parallel loop of the capacitor 4 and the discharge lamp 6. , the behavior is the same.

In this structure, in order to shorten the turn-off time of the transistors 2 and 3, a large reverse voltage is applied between the paste and the emitter. The configuration for this is
This is done by connecting a diode 15.16 in parallel to the resistor 13.14 in the forward direction with respect to the reverse voltage of the transistors 2, 3.

In order to control on/off of the transistor 3 and make its output variable, for example, to dim the discharge lamp 6, or to keep the output current constant even with load fluctuations, the base and emitter of the transistor 3 are connected. A small signal transistor 16 is connected between them. The on/off period of the small signal transistor 16 is controlled by the control circuitry 7. For example, in order to reduce the output current, it is sufficient to shorten the on period of the transistor 3. To do this, the small signal transistor 16 is turned on after the transistor 3 is turned on, but before it is turned off by the voltage of the secondary coil element 2. The signal transistor 16 may be turned on by the control circuit 17.

According to this invention, a series circuit of a constant voltage diode 18 and a diode 19 is connected between the base and emitter of the transistor 3. The constant voltage diode 18 is connected in the opposite direction to the reverse voltage applied to the diode 3 .

Therefore, the reverse voltage applied to the transistor 3 to turn it off is clipped by the constant voltage diode 8, as shown by the chain line in FIG. This prevents a large reverse voltage from being applied to transistors 3 and l6.

Therefore, by being able to use a reverse voltage with a large slope, the time until the transistor 3 is turned off can be sufficiently shortened.

(Effect of the invention)

Claims (1)

[Claims] In a transistor drive circuit comprising a small signal transistor connected between a base and an emitter of a transistor for controlling on/off of the transistor, an electric current is applied between the base and the emitter when the transistor is turned off. A transistor drive circuit comprising a series circuit of a constant voltage diode and a diode connected between the base and emitter of the transistor for clipping the reverse voltage.