JPS5856528A - Driving circuit for semiconductor - Google Patents

Abstract

PURPOSE:To obtain a power converter with small size and high efficiency while attaining high-speed turn-off, by supplying a positive driving current from a driving circuit power supply at turn-on to a control gate of a semiconductor and a negative driving current from a main circuit at turn-off. CONSTITUTION:A transistor (TR)Q1 turns on with a control circuit 3, a voltage is induced to windings n4, n5 of a base driving rransformer TB and a power TRQM is turned on by being supplied with a positive base current. Thus, the base.emitter of a TRQ2 are back-biased with a voltage drop of a diode D2 and the TRQ2 is turned off and a voltage is remained induced in a winding n3 of a main transformer TM. In interrupting a base current to the TRQ1 from the circuit 3, the Q1 is turned off. Thus, the TRQ2 turns on and a negative base current flows to the TRQM through the Q2 from the winding n3 to rapidly turn on the QM. Since the negative base current is obtained from a main circuit at the QM turned off, a driving power supply has only to supply required power for turning-on of the QM, allowing to attain small size.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor drive circuit, and particularly to a drive circuit suitable for turning off semiconductor elements such as power transistors, GTOs, and MOS FETs at high speed.

Conventional drive circuits for no-power transistors have widely used a system in which they are driven via a base drive transformer. This method aims to shorten the turn-off time by causing a base current to flow in the opposite direction by releasing the excitation current accumulated in the base drive transformer. However, in this method, the excitation current accumulated in the base drive transformer changes in proportion to the control time that controls the conduction time of the transistor. This has the disadvantage that the current decreases and the turn-off time of the transistor becomes longer.

However, as for the gate current (hereinafter referred to as off-gate current) required for turning off the GTO, the turn-off time can be shortened by passing a pulse current with a faster rise. To speed up the rise of the off-gate current, it is possible to increase the voltage of the power supply that supplies the off-gate current, but the withstand voltage between the gate and cathode of the GTO is about 20V, Limit the voltage of the power supply. For this reason, the conventional G
In order to turn off the GTO at high speed, the gate circuit of the TO can output a high voltage at the beginning of the off-gate current flow, and as the turn-off progresses, the output voltage of the gate circuit is reduced. This led to complications.

Furthermore, with the increase in capacity of MOSFET, Mo5FE
The equivalent capacitance existing inside T is also larger. M.O.S.
The switching time of Ii"ET is determined by the charging and discharging time of the equivalent capacitance (gate input capacitance) that exists between the gate electrode and the north electrode inside the MO8FET, so the MOSFE
In order to fully utilize the high-speed switching characteristics that characterize T, it is necessary to flow a current with a large peak value during switching, resulting in an increase in gate drive power and an increase in the size of the gate circuit.

In this way, power transistor, GTO.

Semiconductor devices such as MOS and FET all start up quickly at turn-off, and the more a negative polarity drive current with a large peak value is supplied, the shorter the turn-off time becomes and the higher the frequency drive becomes possible, but the lower the drive power becomes. This has led to an increase in the size of the circuit and the complexity of the drive circuit, which has the disadvantage that high-frequency drive cannot be easily realized.

The object of the present invention is to provide a simple configuration, fast start-up, and to obtain a negative polarity drive current with a large beam value from the main circuit.
Turns off the semiconductor at high speed to facilitate high-frequency operation, and reduces the power consumption of the power supply for the semiconductor drive circuit.
The purpose of the present invention is to provide a small, highly efficient power conversion device.

In the present invention, even after a turn-off command is output to the semiconductor,
This method takes advantage of the fact that the semiconductor remains conductive during the storage time. When power is supplied to the load via the main transformer, the semiconductor storage time is such that voltage remains induced in each winding of the main transformer. Therefore, if a winding is provided in the semiconductor to flow a negative drive current, and the turn-off command given to the semiconductor is used to cause the negative drive current to flow, it is possible to obtain a negative drive current during the accumulation time. can.

After the semiconductor is turned off, the voltage induced in each winding of the main transformer disappears, so there is no need to worry about excessive reverse voltage being applied to the control electrode of the semiconductor that has finished its turn-off operation. Therefore, the voltage output from the winding provided in the main transformer through which negative polarity drive current flows can be set to a sufficiently high value, and a negative polarity drive current with a fast rise can be obtained.

An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a case where a single-transistor forward type switching regulator is used, and a transistor QM is used as the semiconductor. In the figure, 1 is the rectifier circuit, CM is the input smoothing capacitor, TM is the main transformer, and 01! n2 t
03 is a winding provided in the main transformer, which is a primary winding, an output winding, and a winding that supplies a negative Ω base current, respectively. 2 is a control circuit 3 and a drive power source that supplies a positive pace current to the transistor QM; 3 is a horizontal output voltage signal Vs that forms a signal that drives the QM so as to keep the output voltage constant; This is a control circuit that

4 is the output rectifier diode, 5 is the output smoothing ac]・/l
-6 is a diode that circulates the current, and 7 is an output smoothing capacitor. 8 and 9 are a diode and a resistor, respectively, which release the excitation current in the TM when the QM is turned off/off. Dl is a diode that blocks the excitation current of TM, R
I is a resistor that limits the negative pace current, Q2 is the winding n
, which blocks the output current of QM until it turns off. TB is a base driving transformer for insulating and passing the positive base current of QM, R2 is a positive base current limiting resistor, and Ql is switched according to the output from 3 to drive QM. transistor,
R2 is a diode that uses the excitation current of TB released when Ql is turned off as the base current of Q2,
At the same time, when supplying a positive base current, it also has the role of reverse biasing the emitter and base of Q2 by a forward voltage drop. R8 is the base current limiting resistor of Q2.

Since the operation of the switching regulator of this configuration is generally well known, a description of the operation will be omitted and only the operation during QM switching will be described.

When the base current is supplied to QL from the control circuit 3, Q
l is turned on, and the winding n of the base driving transformer Tn
4 e A voltage having positive polarity as shown in the black circle is induced in R5, a positive base current is supplied to QM, and QM is turned on. By turning on the QM, a voltage with positive polarity indicated by the black circle in the figure is induced in each winding of the TM, and the voltage of the winding n
, , a current flows through n2. At the same time, a voltage with positive polarity indicated by the black circle in the figure is also induced in the winding n. However, in transistor Q2, since the positive base current supplied to QM flows to diode D2, the positive base current is reverse biased between the emitter and base due to the voltage drop of R2. The off state is maintained reliably while being given to QM. Therefore, during the ON period of 'QM, only a voltage is induced in the winding n3 and the current is QM.
It cannot flow until 2 is turned on.

Next, the turn-off of KQ and r will be described. Control circuit 3
When the base current supplied to transistor Q1 from QL is cut off, QL is turned off.

As a result, a voltage whose polarity is opposite to the black circle shown in the figure is generated in the winding n4 + ``5 due to the exciting current flowing in the transformer TB when Q is conductive, and a voltage is generated from the winding n to the resistor R.
A, current flows through the base and emitter of Q2, and the emitter and base of QM, turning Q2 on. When Q2 turns on, the positive base current of QM is cut off, but QM cannot turn off immediately.
Since the ON state is maintained during the accumulation time, a voltage whose polarity is positive as indicated by the black circles in the figure remains induced in each winding of the main transformer TM. Therefore, when Q2 is turned on, a current flows from the winding n3 through the collector and emitter of Q2, the emitter and base of QM, and the resistor R11 and diode D1, causing a negative base current to flow through QM. The current IR flowing through the winding n when Q2 is turned on is given by the following equation, if voltage drops at various parts of the circuit are ignored.

Here, vCM is the charging voltage of capacitor CM, n, , R
3 is the number of windings in each.

From equation (1), the negative base current of QM can be freely selected depending on the number of turns of R3 and the value of resistor R1, and a sufficiently large negative base current can be supplied to Qv.

The turn-off time of the QM is shortened by the negative base current, and when the QM is turned off, the excitation current flowing in the TM is discharged through the resistor 9 and the diode 8, but at this time, each winding of the TM has a black circle as shown in the figure. A voltage with positive polarity in the opposite direction is generated. This voltage developed in winding 3 is
is blocked by diode D. Therefore, the negative polarity base current applied to the QM is cut off at the same time as the QM is turned off.
, there is no need to worry about applying excessive reverse voltage to the base electrode.

This means that even if the output voltage of the winding n3 is selected to be sufficiently large, an excessive reverse voltage will not be applied to the base electrode of the QM.

Therefore, the output voltage of winding n3 can be selected to be sufficiently larger than the reverse withstand voltage between the base and emitter of Q, and even if there is leakage inductance of Ty, wiring inductance, etc.
A negative base current with a fast rise time can be passed.

Next, when Ql is turned on and a positive base current is supplied to QM, the voltage drop across diode D2 causes
Ql turns off quickly and reliably.

As described above, according to this embodiment, when Q is turned off, a negative base current can be obtained from the main circuit, so the drive power supply 2 has to supply the power necessary for turning on Q. The power required for the driving power source 2 can be approximately 1/2 compared to the conventional method of supplying a negative base current to the QM using the excitation current accumulated in the TB. It goes without saying that along with this, Ts and Q+ can be made smaller.

In addition, in this embodiment, there is no concern that an excessive reverse voltage will be applied to the base electrode of the QM that has completed turn-off, so the winding n
, the output voltage of (I) can be selected to be sufficiently high, and the rise of the negative base current of QM can be made faster.
As shown in the equation (by selecting R and n3, it is possible to obtain a current with a large peak value, so the turn-off time of the QM can be significantly shortened. In this embodiment, it has been confirmed that the QM, which is a turn-off time of .5 μSec, can be reduced to a turn-off time of 0.3 μsec.

FIG. 2 shows an embodiment using GTO.

The operation of each part of the circuit is the same as in the case of FIG.

The well-known power supply, GTO, requires an off-gate current with a large peak value, albeit for a short time at turn-off, which results in an increase in the power of the driving power source 2 and a complicated gate circuit. Also, to turn off the GTO at high speed,
It is essential to speed up the rise of the off-gate current and supply a current with a sufficiently large peak value.

In this embodiment, since the off-gate current of the GTO can be obtained from the main circuit, the power of the drive power supply 2 is reduced and the circuit is miniaturized.
Simplification is possible. As mentioned in the operation in Figure 1, the output voltage of the winding n8 is reversed when the GTO turns off, so there is no need to worry about applying an excessive reverse voltage to the gate electrode of the GTO, and the output voltage of the winding n3 is reversed. The output voltage can be selected to be higher than the reverse withstand voltage between gate and cathode. This means that an off-gate current with a large peak value and a fast rise can flow, and the GTO can be turned off quickly.

FIG. 3 shows an example in which a MOS FET is used.

The MOS FET shown in the diagram is 10s F to N channel.
ET, which is a semiconductor device that conducts when the gate electrode is positively biased with respect to the source electrode and turns off when the bias voltage is removed. In this embodiment, QM in the embodiment of FIG. 1 is MoB2, Q2 is MOS2,
Ql is replaced with MOS3, and the circuit operation is the same as in FIGS. 1 and 2.

Compared to transistors, GTOs, etc., MOS FETs have superior features such as faster switching speed and lower gate drive power.

The switching speed of MOS FET is 8f's FE
The switching speed is largely dependent on the equivalent capacitance existing inside the T, and is determined by the charging/discharging time of the equivalent capacitance (hereinafter referred to as human power capacity) existing between the gate and source electrodes.

Further, the driving power of the MOS FET is also determined by the charging/discharging energy of the human power capacity.

Recently, the capacity of 408 PET has been increasing, and accordingly, the input capacity has also tended to increase.

Accordingly, in order to fully utilize the characteristics of MOSFETs such as high-speed switching characteristics and low driving power, a gate circuit that can supply a gate current with a large peak value with low loss is required.

According to this embodiment, only the power for charging the input capacitance is obtained from the drive power supply 2, and the power for discharging is obtained from the main circuit, so even if the input capacitance of the MOSFET increases, the drive power supply 2
without significantly increasing power. In addition, as described in the embodiments shown in Figures 1 and 2, since the power to discharge the input capacitance is obtained from the main circuit, the input capacitance can be discharged in a short time, and the input capacitance of the MOSFET increases. However, the high-speed turn-off characteristics are not lost.

FIG. 4 shows an embodiment in which the present invention is applied to an inverter. In the figure, CM[+CM2 is the input smoothing diode, QM[y QM2 is the main switching transistor, TBI and TB2 are QMl and QM2, respectively.
Base drive transformer for driving n41 + n
51 + "42 + "52 are each TnI.

Primary and secondary windings installed in Tn2, TM is the main transformer, nl
+ n2 + n31 + n32 is the winding provided on Ty, D5 and Do are diodes that rectify the output of windings n3□ and n32, and R4-R5 are QMt + QM, respectively.
A resistor Qa limits the negative polarity base current of No. 2.

Q4 is a transistor that switches the negative polarity base current of QM t t QM 2, respectively, D3'+D4
are the diodes for making this current the base current of Qs and Q when the excitation current of Tn L and TB 2 is released, Ra and R are the base current limiting resistors of Q31 and Q4, respectively, and Q, , and Qe are the base current limiting resistors of Q31 and Q4, respectively. QM(,Q
M2 driving diode, D.

D8 is an output rectifying diode.

The illustrated circuit is widely known as a half-bridge inverter circuit, and a description of the inverter operation will be omitted. When a base current is supplied from the control circuit 3 to the transistor Q, Qa is turned on, and a positive base current is supplied from the drive power supply 2 to QMI via the base drive transformer Tnl, making QMI conductive. state. QMI
Due to the conduction of the capacitor CMI to the winding n1 of TM
A current flows through the winding 02, power is supplied to the load from the winding 02, and a voltage whose polarity is positive as shown by the black circle is induced in the winding n31+03□. Since the current in the winding n31 is blocked by the transistor Q3 and the current in the winding n32 is blocked by the diode D6, only a voltage is induced in both windings and no current flows.

Next, when the base current supplied from the control circuit 3 to Q is cut off and Qa is turned off,

During the ON period of Q, the excitation current accumulated in TnI is released through the resistors Ra, the base and emitter of Qa, and the emitter and base of QMI, turning Qa on. Q
Immediately after the turn-on of , QM l (7) Depending on the accumulation time, a voltage whose polarity is positive as indicated by the black circle in the figure is induced in each winding of the main transformer TM, and from the winding n31 to the collector and emitter of Qa. , the current flows through the emitter and base of QMI, turning it off at high speed. When QMI is turned off, a voltage with positive polarity in the opposite direction to the black circle shown is induced in each winding of TM, but the voltage of winding n3t is blocked by diode D, and the voltage of winding n32 is blocked by transistor Q4. , no current flows. When QM2 operates, each part works in the same way, turning QM2 on and off at high speed.

According to this embodiment as well, the same effects as in FIG. 1 can be obtained.

Furthermore, the present invention can be implemented in the same manner when GTO and MOS FET are used in the No.-7 bridge inverter circuit as shown in FIGS. 2 and 3.

Further, it is clear from the embodiments shown in FIGS. 1 to 4 that this embodiment can be applied to a push-pull inverter, a bridge inverter, a one-stone power converter, etc.

According to the present invention, since the start-up is fast and a negative drive current with a large peak value can be supplied from the main circuit to the semiconductor, the semiconductor can be turned off at a speed approximately five times faster than in conventional circuit systems. , and high-frequency operation can be achieved with a simple drive circuit. The power of the power supply for the semiconductor drive circuit can be reduced to 1/2 or less of the conventional power supply, which has the effect of providing a compact and highly efficient power conversion device.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the invention, and FIGS. 2 to 4 are diagrams showing other embodiments of the invention. QMI QM l + QM2...Main switching transistor, GTO...Gator/off thyristor, MO8I...MOS FET, TM...Main transformer, TB...Base drive transformer, n3 p" 31
+ n32...Negative polarity drive current supply winding, Q2,"
MOS2. Qs, Q4...Negative 1 Fig. 2

Claims (1)

[Scope of Claims] 1. In a semiconductor drive circuit that supplies a positive drive current to a semiconductor control @1 electrode at turn-on and a negative drive current at turn-off, the positive drive current is A semiconductor drive circuit, characterized in that a drive current of negative polarity is supplied from a main circuit, and the drive current of negative polarity is supplied from a main circuit. 2. A semiconductor drive circuit according to claim 1, wherein the negative drive current is supplied from a winding provided in a transformer that supplies power to a load. 3. In claim 2, the winding that supplies the negative drive current is connected to the semiconductor control electrode and one main electrode via a semiconductor switch and a first diode. Characteristic semiconductor drive circuit. 4. In claim 3, the positive polarity drive current is supplied from the drive circuit power source via a drive transformer, and the semiconductor switch is turned on by discharge of excitation current from the drive transformer. A semiconductor drive circuit characterized by being configured to perform the following functions. 5. In claim 4, the output winding of the drive transformer is connected at one end to a semiconductor control electrode and at the other end to one main electrode of the semiconductor through a second diode. A semiconductor drive circuit characterized in that the control electrode of the semiconductor switch is connected to the cathode side of the second diode, and the one main electrode is connected to the anode side.