JPS60154712A - Transmission driving circuit - Google Patents

Abstract

PURPOSE:To decrease the turn-off time of a switching transistor (TR) and also to decrease the switching loss by providing a tertiary winding to a drive transistor and flowing a collector current of the switching TR to the said tertiary winding. CONSTITUTION:A switch SW turned on/off in response to an input signal is connected in series to a primary winding N1 of a drive transformer T', one end of a secondary winding N2 of the drive transformer T' is connected to a base of the switching TRQ via a forward bias limit resistor R1, and also the other end of the secondary winding N2 is connected to an emitter of the switching TRQ and a reverse bias limit resistor R2 is connected between the base and emitter of the switching TRQ. A reverse bias diode D1 is connected in parallel with the forward bias limit resistor R1 and the tertiary winding N3 of the drive transformer T' is connected in series with the collector of the switching TRQ.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a transistor drive equivalent for driving a high power e-high speed operation type switching transistor connected in series with a coil or a coil and a capacitor.

[Background technology]

For example, a step-up transistor chopper is configured such that a switching transistor is connected in series with a coil or a coil and a capacitor, and the switching transistor is turned on and off to supply power to a load.

Collector current in the above switching transistor! . The triangular wave current shown in Fig. 1(a) or the triangular wave current shown in Fig. 1(b)
) A slow-phase current flows as shown in (). In addition, Fig. 1(b)
In the figure, the shaded area is the current flowing through the diode connected in parallel to the switching transistor.

The above switching transistor is used for high power applications.
Switching loss is a particular problem. That is, the collector current I of the switching transistor. is shown in Figure 1 above (
Because of the waveforms in a) and (b), if a reverse bias current does not flow from the emitter to the base of the switching transistor when the voltage changes from on to off, it will take time for the accumulated charge in the switching transistor to dissipate, resulting in a longer turn-off time. This has the disadvantage that it affects the control range of the switching transistor and increases switching loss. Especially when the frequency is high, it is necessary to flow a reverse bias current to shorten the turn-off time.

FIG. 2 shows a circuit diagram of a transistor drive circuit for driving such a switching transistor. This transistor drive circuit connects a switch SW in series to the primary winding Nyu of the drive transformer T, and connects one end of the secondary winding N2 of the drive transformer T to the switching transistor Q through a forward bias current limiting resistor R1. 2 along with connecting to the base
The other end of the secondary winding N2 is connected to the emitter of the switching transistor Q, and the induced voltage in the secondary winding N2- of the drive transformer T due to the disconnection of the primary winding N of the drive transformer T due to the on/off of the switch SW. The rising edge 9 of is passed through the current limiting resistor R to the base of the switching transistor Q. However, in the case shown in FIG. 2, when the switching transistor Q changes from on to off, a sufficient reverse current cannot flow through the base. Therefore, there is a drawback that the switching loss of the switching transistor Q is large.

FIG. 3 shows a circuit diagram of another conventional transistor drive circuit for driving the switching transistor. This transistor drive circuit has a reverse bias current limiting resistor R3 connected between the base and emitter of the switching transistor Q in FIG. 2, and reverse bias diodes D, . The induced voltage of the secondary winding N2 of the drive transformer T is passed through the biasing current limiting resistor R1 to the base of the switching transistor Q, and reverse bias is applied when the input signal changes from on to off. The emitter is connected in parallel with the current limiting resistor R2.
A reverse bias diode D1 is passed between the switching transistors Q to flow a reverse bias current.
Although the switching loss is lower than that of the circuit shown in FIG. 2, this circuit also has the disadvantage that as the switching speed increases, the switching loss increases.

[Purpose of the invention]

An object of the present invention is to provide a transistor drive circuit capable of reducing switching loss by shortening the turn-off time of a switching transistor.

[Disclosure of the invention]

The transistor drive circuit of the present invention is a transistor drive circuit that drives a switching transistor connected in series to a coil, and has a primary winding and a secondary winding wound with the same polarity and a winding with opposite polarity. A switch that turns on and off according to an input signal is connected in series to the primary winding of a drive transformer consisting of a tertiary winding wound around a tertiary winding. A reverse bias current limiting resistor is connected between the base and emitter of the switching transistor, and a reverse bias current limiting resistor is connected in parallel with the forward bias current limiting resistor. ,
The tertiary winding of the drive transformer is connected in series to the collector of the switching transistor.

In this way, the tertiary winding (opposite polarity to the secondary winding) of the drive transformer is connected in series to the collector of the switching transistor, and the collector current of the switching transistor is caused to flow through the tertiary winding of the drive transformer. A steep reverse bias can be applied between the base and emitter via a drive transformer. For this,
The turn-off time of the switching transistor can be shortened.

An embodiment of this invention will be described based on FIG. 4. In this transistor drive circuit, a switch SW that turns on and off according to an input signal is connected in series to the primary winding N of the drive transformer T', and one end of the secondary winding N of the drive transformer T' is set to forward bias. The current limiting resistor R2 is connected to the base of the switching transistor Q via a current resistor R, and the other end of the secondary winding N2 is connected to the emitter of the switching transistor Q, and a reverse bias current limiting resistor R2 is connected between the base and emitter of the switching transistor Q. A reverse bias diode D□ is connected in parallel to the forward bias current limiting resistor R, and the tertiary winding N3 of the drive transformer T' is connected in series to the collector side of the switching transistor Q. In this case, the drive transformer T' is wound so that the primary winding N and the secondary winding N have the same polarity, and the tertiary winding N, 3 has the opposite polarity to the secondary winding N2. There is.

Next, the operation of this transistor drive circuit will be explained.

Collector current I flowing into switching transistor Q.

As mentioned above, is a triangular wave, so when the switching transistor Q changes from off to on, when an on signal is sent to the human power, the switch SW turns on, and an electromotive force is generated in the primary winding aN of the drive transformer T'. This electromotive force generates a voltage in the secondary winding N2, causing a constant current to flow through the forward bias current limiting resistor R□ to the base of the switching transistor Q, turning on the switching transistor Qe. Furthermore, since the collector current increases from 0 to 0 when the switching transistor Q turns on, the current changes from off to on, resulting in an overdrive state, and there is almost no switching loss. Next, while the switching transistor Q is on, the collector current I. is an increasing function, an electromotive force is also generated in the tertiary winding N3, and since the tertiary winding N3 and the secondary winding N are in opposite directions, the voltage generated in the primary winding N and The voltage developed from the tertiary winding N3 cancels out, causing the base current to decrease somewhat over time. Therefore, the base current IBf'i just before the switching transistor Q turns from on to off is the collector current at that time! . It is necessary to make it 1/h or more.

Next, when the switching transistor Q, which is effective in this invention, is in a state where it changes from on to off, when an input button off signal is sent, a pulsed electromotive force opposite to that when it is on is generated in the drive transformer T'. However, an opposite voltage is also applied to both ends of the secondary winding N2. Furthermore, at the moment when the base current is turned off due to the storage time of the switching transistor Q, the collector current ■. Since the emitter is about to increase, an electromotive force is generated in the tertiary winding N3 in the same direction as when it is turned on. Therefore, a reverse voltage is applied to the secondary winding N, the back electromotive force from the primary winding N and the electromotive force from the tertiary winding N3 are superimposed, and a large reverse bias is applied to the base of the switching transistor Q. Current flows.

By the above operation, the storage time of switching transistor Q becomes extremely short, and switching loss is reduced.

Note that the operations of the reverse bias diode D and the reverse bias current limiting resistor R2 are similar to those in FIG.

FIG. 5 shows a circuit diagram of a boost type transistor chopper using the transistor drive circuit of the above embodiment. This step-up transistor chopper has a DC input voltage (completely smooth or pulsating current) and a collector current of ■. is a triangular wave, the operating frequency is 40 to 50 KHz, and the on period of the switching transistor Q can be freely controlled by changing the duty. When an on signal is input to the control input, the switching transistor Q is turned on and energy is stored in the coil L. Next, an off signal is input, and the switching transistor Q is rapidly turned off by the operation described above, and the energy stored in the coil L□ charges the smoothing capacitor C1 through the diode D.

In particular, when the switch SW changes from on to off, the collector current ■. indicates a peak value, so the storage time of the switching transistor Q should be as short as possible. Load LD
is not limited.

6(C) and (d) show the collector tfiI of the switching transistor Q in the circuit section of FIG. 5. Figures 6(a) and 6(b) show the waveforms of the switching transistor Q in a conventional step-up transistor chopper in which the base drive circuit in Figure 5 is changed to that in Figure 3. tit.

and base current 1. The waveform of B is shown. As is clear from this figure, in the conventional waveforms shown in Figures 6(a) and 6(b), the reverse bias applied to the switching transistor Q is low, so the turn-off time of the switching transistor Q is long; Figure 6 (c), (d)
In the example waveform, since the reverse bias input to the switching transistor QK is steep and high, the turn-off time of the switching transistor Q is short.

FIG. 7 shows an example of a circuit in which the circuit shown in FIG. 4 is used in a transistor half-bridge inverter.

In FIG. 7, 1 and 2 are terminals, L2 coils, C2 and C3 are capacitors, D3. D is a diode, Q, Q
2 is a switching transistor, T2 is a drive transformer, R3 and R5 are forward bias current limiting resistors, R4 and R6
is a reverse bias current limiting resistor, D5' and D6 are reverse bias diodes, and SW□ and SW are switches.

This transistor type half-bridge inverter uses a DC voltage obtained by rectifying and smoothing the input voltage AC100V to terminals 1 and 2.
A slow phase current flows through the switching transistor Q2. In this circuit example as well, the current waveform becomes an increasing function of time from 0, so by applying the circuit of FIG. 4, it was possible to increase the switching speed and reduce the switching loss.

In this way, the transistor drive circuit of this embodiment has almost no addition to the conventional circuit side, that is, the tertiary winding N3 is provided on the drive transformer T', and the tertiary winding N3 is Collector current I of switching transistor Q.

Collector current I when switching transistor Q changes from on to off state with a simple configuration where only t- is allowed to flow.

A pulsed reverse bias current is applied between the base and emitter of the switching transistor Q through the drive transformer T' due to the change in the switching transistor Q, so that the turn-off time of the switching transistor Q is shortened and the switching loss is reduced. I can do it. Further, by shortening the switching time, the control range of the switching transistor Q at high frequencies can be widened.

〔Effect of the invention〕

According to the transistor drive circuit of the present invention, the turn-off time (M during storage) of the switching transistor can be shortened, and therefore switching loss can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a collector current waveform diagram of a switching transistor, FIGS. 2 and 3 are circuit diagrams of conventional transistor drive circuits, FIG. 4 is a circuit diagram of an actual example of the present invention, and FIG. 5 is a circuit diagram of a conventional transistor drive circuit. A circuit diagram of a step-up transistor drive circuit using the circuit shown in Figure 4, Figure 6 is a waveform diagram of the collector current and pace current of the switching transistor in the conventional example and the embodiment, and Figure 7 is a circuit diagram using the circuit shown in Figure 4. This is a circuit diagram of a transistor type half-principal engine. T'...drive transformer, SW...switch, Q...
・Switching transistor, R work... Current limiting resistor for forward bias, R2... Current limiting resistor for reverse bias, D□・
・Reverse (diode for IAS, N...primary winding,
[

Claims (1)

[Claims] A transistor drive circuit that drives a switching transistor connected in series to a coil, comprising a primary winding and a secondary winding wound with the same polarity, and a tertiary winding wound with the opposite polarity to the secondary winding. A switch that turns on and off according to an input signal is connected in series to the primary winding of a drive transformer, and the secondary winding m of the drive transformer is connected between the base and emitter of the switching transistor via a forward bias current limiting resistor. and the pace of said switching transistor.
A transistor in which a reverse bias current limiting resistor is connected between the emitters, a reverse bias diode is connected in parallel with the forward bias current limiting resistor, and the tertiary winding of the drive transformer is connected in series to the collector of the switching transistor. drive circuit.