JPS59161122A - Driving circuit of transistor - Google Patents

Abstract

PURPOSE:To execute at a high speed a turn-off operation of a transistor to be driven, by using an MOSFET for a turn-off control of the transistor to be driven, and also adding a winding to a transformer. CONSTITUTION:A series circuit of a winding 5 of a transformer and a diode 8A is connected between the gate and the source of a transistor to be driven TR9, by the polarity by which the TR9 is turned on when a TR2 of a driving switch element is turned on. Also, the source and the drain of an MOSFET 10A (N channel type) for a turn-off control of the TR9 are connected to the gate and the source of the TR9, respectively. Moreover, the gate and the source of the FET10A are connected to both ends of other winding 5A provided on a transformer 3A. By forming in this way, a turn-off operation of the transistor to be driven is executed at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a circuit for driving a transistor at high speed through a transformer.

[Prior art]

In order to drive a transistor at high speed, in the case of a bipolar transistor, a circuit with a small driving impedance is needed between the pace and the emitter to supply current to the pace with a small drive impedance when it is turned on, and to rapidly draw out the accumulated charge in the pace when it is turned off. Need to connect.

Further, in the case of a MOS FET (insulated gate field effect transistor), high-speed switching operation of the MOS FET can be obtained by rapidly charging and discharging the gate-source capacitance using a circuit with a small driving impedance.

FIG. 1 is a circuit diagram of an example of a conventional transistor drive circuit, which is for a circuit that drives a transistor via a transformer, and FIG. 2 also shows its operating waveform diagram.

Here, 1 is an input power supply, 2 is a drive switch element transistor, 3 is a first winding 4. Second winding 5. A transformer has a sixth winding 6, 7.8 is a diode, 9 is a driven transistor MO8FET 110 is a transistor for controlling its turn-off, and 11 is a resistor. In FIG. 2, ■C'E is between the collector and emitter 1' of transistor 2! VG8 is the MO8FET 9 gate-to-source voltage.

The transistor 2 is connected in series with the human power source 1 and the first winding 4, the third winding #6 and the diode 7 are connected in series at both ends of the human power source 10, and the second winding 5 is connected at one end to the source S of the MO8FET 90, and at the other end to the gate G of the MOS FET 9 through the diode 8 in the forward direction. The transistor 10 has its emitter connected to the gate q of the MOS FET 9, its collector connected to the source S of the MOS FE'l' 9, and its base connected to the anode of the diode 8 through a resistor 11.

First, when the transistor 2 is turned on at time t0, the voltage of the input power source 1 is applied to both ends of the first winding 40, so that
The induced voltage generated across the second winding 5 is
Apply a positive voltage to the gate G of MOS FET 9 through diode 8 to turn it on (M
It is assumed that OS FET q is of N-channel type.

). At this time, the gate-source capacitance of the MOSFET 9 is rapidly charged because the drive circuit system does not include a resistance element, and the turn-on operation of the MOSFET 9 is performed at high speed.

When the transistor 2 is turned off at time t1, a voltage of opposite polarity is generated in each winding of the transformer 6 (in FIG. 1, the black circle end indicating the winding start direction is of negative polarity).

At this time, the emitter potential of the transistor 10 is set to MOS FE by the charging voltage of the gate-source capacitance.
It is at a positive polarity of 6.degree. with respect to the source potential of T9. Therefore, the anode of the diode 8 becomes a negative potential, and a base current flows from the emitter of the transistor 10 through the resistor 11, turning the transistor 10 on.

Therefore, the MOS FET 9 turns off at a relatively high speed because the charge stored in its gate-source capacitance is discharged from the emitter to the collector of the transistor 10.

MOS FET 9 Nogate-7 WL pressure Vas
Even if becomes 0, a negative voltage is induced in the second winding 5, so the transistor 10 has a base current flowing from the collector through the resistor 11 while its emitter current remains 0. continue.

Here, if the excitation energy of the transformer 3 during the period from time t0 to t is not completely released within the period from time t1 to t, the magnetic core of the transformer 6 will become saturated due to the accumulation of excitation energy. .

Therefore, the excitation energy is released and regenerated (recovered).
In order to do this, a regeneration path is provided from the sixth winding 6 through the diode 7 to the human power source 1. Through this regeneration path, transistor 2
The collector-emitter voltage of the winding 4 is made to increase only up to a predetermined value, and the predetermined value is determined by the turns ratio between the first winding 4 and the sixth winding 6.

However, as described above, in addition to the regeneration path, there is a path through which current flows from the collector of the transistor 10 to the second winding 5 through the resistor 11.

If the resistance value of the resistor 11 is sufficiently large, the collector-emitter voltage V ('E) will be a high voltage as shown in the waveform (■) in Figure 2, but an induced voltage of opposite polarity will exist in each winding. In addition, when the resistance value is small, the terminal voltage of the second winding 5 decreases as shown in waveform (■) in Fig. 2, but the excitation energy discharge period is short. If the discharge period becomes longer and the resistance value is even smaller, the excitation energy of the transformer 3 cannot be completely discharged before the transistor 2 becomes conductive again, as shown by waveform (3) in FIG.

On the other hand, at time t, in order to rapidly discharge the charge accumulated in the gate-source capacitance of the MOS FET 9, it is necessary to flow a sufficiently large collector current through the transistor 10. The resistance value of the transistor 100 must be made small to allow a sufficiently large base current to flow through the base of the transistor 100.

In this way, in the conventional example described above, the lower limit of the resistance value of the resistor 11 is limited in order to release the excitation energy of the transformer 3 in a short period of time, so that a sufficiently large base current is supplied to the transistor 10. I can't. In other words, the MOS FET 9 cannot rapidly release the charge accumulated in its gate-source capacitance,
It was difficult to speed up the turn-off operation. In particular, MOS
If FET 9 is a large power device, its gate
Since the source-to-source capacitance is extremely large, it becomes more difficult to speed up the turn-off operation.

In addition, as described above, even in the state where the emitter current of the transistor 10 becomes 0 after the charge of the capacitance between the gate and source of the MOSFET 9 is completely discharged, the transistor 10 continues to transfer its base current to the collector. - Since it continues to flow through the lid, its base will have a large base accumulated charge.

However, even after the discharge of the excitation energy of the transformer 6 is completed and the supply of base current to the transistor 100 is stopped, the charge accumulated in the base of the transistor 100 is transferred to the resistor 1 having a relatively high resistance value.
The base current continues to flow until time t when application of a positive drive signal between the gate and source of the MOS FET 9 is started.

Therefore, at the moment when transistor 2 is turned on at time t, transistor 10 is also turned on, and due to the positive voltage generated in second winding 5, transistor 10 continues to operate until its base accumulated charge is completely discharged. The on state continues during the transient period of .

That is, the load of the transistor 2 has an apparent low impedance, and an excessive current flows through its collector. This results in an increase in power loss, and also causes a delay in the effective turn-on time of the MOS FET 9 due to the coincident period in which the transistors 2 and 10 are in the on state.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and improve the turn-off operation of a driven transistor.

An object of the present invention is to provide a transistor drive circuit capable of speeding up turn-on operation and reducing power loss of a drive switch element.

[Summary of the invention]

The present invention provides an M, in which a control signal application terminal has a high impedance, for controlling the turn-off of a driven transistor.
By using an OS FET and supplying its control signal from another winding installed in the transformer, it is possible to shorten the period for releasing the excitation energy of the transformer and to speed up the turn-off operation of the driven transistor. It is something that I will do.

・ 8 ・ In other words, the configuration of the transistor drive circuit according to the present invention is such that the first winding of the transformer and the drive switch element are connected in series with the input power source, and the drive switch element is turned on and off. In a transistor drive circuit that drives a driven transistor with a pulse generated in the second winding of the transformer by A series circuit of the winding No. 2 and the diode is connected with a polarity that turns on the driven transistor when the drive switch element is turned on, and the source (or emitter) and gate (or base) of the driven transistor are connected. , M for turn-off control of the driven transistor, respectively.
The source and drain of the OS FET are connected with polarity according to the channel format, and the gate and source of the MO8FET are connected to both ends of the other winding provided in the transformer. .

[Embodiments of the invention]

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

FIG. 6 is a circuit diagram of an embodiment of a transistor drive circuit according to the present invention.

Here, Sk is the first winding 4 similar to the transformer 6 in FIG.
．． Second winding 5. In addition to the third winding 6, a fourth winding 5A
8A is a diode, 10A is a MOS FET (N
channel type), and other symbols are equivalent to the same symbols in FIG.

The drain D and source S of MOS FET i OA are connected to the gate G and source S of MOS FET 9, respectively, and the gate G of MOS FET 10A is connected to the end of the fourth winding 5A (black circle). The winding start end (the side opposite the mark) is connected to MO8FET1
Connected to source S of 0A.

First, when transistor 2 turns on, MOSFET 9
The operation of turning on is the same as the conventional example shown in FIG. That is, since a positive polarity voltage is induced at the winding start end of the fourth winding 5A, a negative polarity voltage is applied between the gate and source of the MOS FBT 1oA, and the MOS FBT 1oA is in an off state.

When transistor 2 is turned off, a negative voltage is induced at the beginning of the fourth winding 5A, so MOS FET 1
0A is turned on when a positive voltage is applied between its gate and source. This is more than a trap, MOS Fllff
The charges accumulated in the gate-source capacitance of No. 9 can be rapidly released.

Furthermore, since a MOS FET with a small capacitance of 1oA is sufficient, its gate-source capacitance is also smaller than that of the MOS FET.
It is sufficiently smaller than that of FBT9. therefore,
For the period from time t1 to time t in Fig. 2, the capacitance is large as a load impedance connected to the fourth winding 5A, and its influence on the release of the excitation energy of the transformer 3A is extremely large. small.

That is, the excitation energy can be completely regenerated to the human power source 1 through the sixth winding 6 and the diode 7, so that its release period is completed in a short period of time as in waveform I in FIG. Furthermore, 11. Immediately before transistor 2 turns on at time t, the terminal voltage of the fourth winding Jl15A is 0 and te MO8
Since FET 10A is already in the off state, MOS FET 1 is turned on at the time when transistor 2 is turned on.
0A does not appear as a driving load for the transistor 2.

As described above, according to this embodiment, it is possible to discharge excitation energy at high speed, and the 1MO8FET 10A
It is clear that the increase in power loss due to K and the delay time of the turn-on operation of MOSFET q do not occur.

Next, FIG. 4 is a circuit diagram of another embodiment of the transistor drive circuit according to the present invention.

Here, 3B is the first winding 4 similar to the transformer 3 in FIG.
．． Second winding 5. In addition to the third volume a6, the fourth volume 55B
8B is a diode, 10B is a MOS FET (P
channel type), and other symbols are equivalent to the same symbols in FIG.

・12・The source S of MOS FET q is connected to the end of the second winding 50 through a diode 8B in the forward direction, and the MO
The gate G of SFF1T 9 is connected to the winding start end of the second winding 5. The drain D and source S of the MOS FET 1oB are connected to the source S and gate G of the MOS FET 9, respectively, and the gate G of the MOS FET 1oB is connected to the winding start end of the fourth winding 5B. The winding end of the fourth winding 5B is MO8FETiOB
is connected to source S of

When the transistor 2 is turned on, the voltage induced in the second winding 5 is transferred to the MOS FET through the diode 8B.
It is applied between the gate and source of MOS F9 and turns on MOS F9.

At this time, since a positive voltage is induced in the fourth winding 5B at the beginning of the winding, a positive voltage is applied between the gate and source of the MOS FET 1oB, and the MOS FET 1oB is in an off state.

When the transistor 2 is turned off, a negative voltage is induced at the beginning of the fourth winding 5B, so that the MOS F
ET 1oB is turned on and discharges the charge stored in the gate-source capacitance of MO8FBT 9.

In this way, since the same operation as in the embodiment of FIG. 3 is performed, the effect is also the same as described above.

In each of the embodiments described above, the operation has been explained using the MOS FET 9 as an example of the driven transistor. This is equivalent to the operation of discharging charge, and MOS FET 9
Similarly, high-speed turn-off operation is possible even if the transistor is replaced with a bipolar transistor.

In addition, the series circuit of the third winding 6 and the diode 7 can be used as a surge absorption circuit generally called a snubber circuit, such as by connecting a series circuit of a capacitor and a resistor between the terminals of the first winding 4. Even if replaced, the excitation energy of the transformers 5A and 5B can be released in the same way as in any of the embodiments described above.

This is not directly related to the operation and effects of the present invention. .

It is clear that the transistor 2 can be replaced with any switching element that can provide an on/off function.

〔Effect of the invention〕

As described above in detail, according to the present invention, it is possible to speed up the turn-off and turn-on operations of the driven transistor, shorten the excitation energy release period of the transformer, and further reduce the power loss of the drive switching element. The effect is remarkable.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an example of a conventional transistor drive circuit, FIG. 2 is an operating waveform diagram thereof, FIG. 3 is a circuit diagram of an embodiment of a transistor drive circuit according to the present invention, and FIG. 4 is a circuit diagram of an example of a conventional transistor drive circuit. It is a circuit diagram of another example similarly. 1... Input power supply, 2... Transistor, 3A, 3B... Bent transformer, 4... First winding, 5... Second winding, 5A, 5B...
Fourth winding, 6...Third winding, 7, 8A.・15.

Claims (1)

[Claims] 1. The first winding of the transformer and the drive switch element are connected in series to the human power source, and the second winding of the transformer is exposed to pulses generated when the drive switch element turns on and off. In a transistor drive circuit that drives a drive transistor, a switch element drives a series circuit of a second winding of a transformer and a diode between the gate (or pace) and source (or emitter) of the driven transistor. M for turn-off control of the driven transistor is connected to the source (or emitter) and gate (or pace) of the driven transistor, respectively.
The source and drain of the OS FET are connected with polarity according to the channel format, and the gate and source of the MO8FET are connected to both ends of the other winding provided in the transformer. A transistor drive circuit for