JPH0545095B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for a gate turn-off thyristor, and more particularly to a turn-off control circuit for a gate turn-off thyristor whose cathode side is connected to an inductive load.

[Conventional technology]

A gate turn-off thyristor (hereinafter referred to as GTO) is turned on by applying current to its P gate or drawing current from its N gate, and turned off by drawing current from its P gate, like a normal thyristor. The turn-on control circuit is configured similarly to a normal thyristor,
The turn-off control circuit includes a turn-off gate P as described in Japanese Patent Laid-open No. 59-14355.
The configuration is such that a transistor is connected between the gate and cathode.

The turn-off control circuit of this method is shown in Fig. 2a,
As shown in b, there are two connection positions for the transistor depending on the relationship between the GTO and the load.

The one in Fig. 2a has an anode 1a, an N gate 1
GTO consisting of b, P gate 1c, and cathode 1d
1, load 2 has an anode 1a and a load power supply 3.
connected between the positive electrode of GTO1 and the cathode 1d of GTO1.
and the negative electrode of the power supply 3 are connected to the ground potential line 4, the collector and emitter of the off transistor 5 are connected in parallel with the gate resistor 6 between the P gate 1c of the GTO 1 and the ground potential line 4, and the off transistor 5 is connected to the ground potential line 4.
A turn-off pulse signal generation circuit 7 is connected between the base of the power supply 1 and the ground potential line 4. The turn-on control circuit is omitted.

In this circuit, when the GTO 1 is to be shifted from the on state to the off state, the turn-off pulse signal generating circuit 7 turns the off transistor 5 on. Collector-emitter voltage V _CE when off transistor 5 is on is P-gate-cathode potential V _GK when GTO1 is on
When compared with V _CE <V _GK 0.6 [v] (1), current can be extracted from the P gate 1c. In order to do this, the off transistor 5 needs to operate in saturation.

When the current flowing to the anode 1a when GTO1 is on is I _A , and the maximum gate current drawn from the P gate 1c when GTO1 is off is I _G , the turn-off gain is I _A /I _G3-5 ...(2), and the value of equation (2) changes depending on the structure of GTO1 and process constants. Since the gate current I _G is equal to the collector current I _C of the OFF transistor 5 and the OFF transistor 5 is in saturated operation, the collector-emitter saturation voltage V _CES of the transistor 5 when the maximum gate current I _G flows is V _CES <0.6 [v] …(3) is satisfied. The collector-emitter saturation voltage V _CES of the transistor 5 when a sufficient base current is supplied is determined mostly by the collector internal resistance R _c . Collector internal resistance R _C is inversely proportional to the geometric dimensions of transistor 5,
When trying to integrate GTO1 and its control circuit on a single silicon substrate, the collector internal resistance
If an attempt is made to obtain a transistor 5 with a small R _C , the chip will become larger and more expensive. Japanese Patent Publication No. 59-14355
As described in the publication, if a diode or a resistor is inserted between the cathode 1d of GTO1 and the ground potential line 4 to increase the cathode potential _VK of GTO1, the collector of transistor 5 in equation (3) The emitter saturation voltage V _CES only needs to satisfy V _CES < V _GK + V _K 0.6 + V _K (4), and a small transistor structure with a high collector-emitter saturation voltage V _CES is required by the increase in cathode potential V _K. can do.

In the case of FIG. 2b, the load 2 is inserted between the cathode 1d of the GTO 1 and the ground potential line 4, and the gate resistor 6 is connected between the P gate 1c and the cathode 1d. When GTO1 is off, the cathode potential V _K is almost equal to the ground potential, but when GTO1 is on, the cathode potential V _K is the voltage of power supply 3.
Approximately equal to V _CC . When shifting the GTO 1 from the on state to the off state, the off transistor 5 is turned on. At this time, the collector-emitter voltage V _CE of the off transistor 5 changes from approximately the voltage V _CC of the power supply 3 to the saturation voltage V _CES , and the operation of the transistor 5 changes from an active state to a saturated state.

In this example as well, the turn-off gain in equation (2) is the same. When the GTO 1 starts to change from the on state to the off state, the off transistor 5 is active and can draw out a sufficient gate current I _G. However, as GTO1 approaches the off state, the collector potential of transistor 5 approaches zero, so the gate current drawing operation
The result will be similar to the case in Figure a. That is, the base bias current of the off transistor 5 is I _B ,
When the emitter grounded current amplification factor is h _FE , it is necessary that I _G <h _FE・I _B (5).

However, unless load 2 is a constant current load, GTO
As the transistor 1 shifts to the off state, the potential of the cathode 1d decreases, and as a result, the anode current I _A also decreases, so it is not necessary to make the collector internal resistance R _C of the off transistor 5 as small as in the case of FIG. 2a. , the geometric dimensions of transistor 5 can be correspondingly reduced.

However, when the load is an inductor and it is a motor winding, GTOs 9 and 10 are connected to both sides of the motor winding 8, as shown in FIG.
The GTO 9 consists of an anode 9a, an N gate 9b, a P gate 9c, and a cathode 9d. A motor winding 8 is connected to the anode 9a side, and a current detection resistor 11 is connected between the cathode 9d and the ground potential line 4. . The collector and emitter of the off transistor 12 are connected in parallel with the gate resistor 13 between the P gate 9c of the GTO 9 and the ground potential line 4, and the turn-off pulse signal generation circuit 14 is connected between the base and the ground potential line 4. be done. GTO1 N gate 9
A description of the turn-on control circuit connected to b is omitted. The current detection resistor 11 has a small value, and the relationship among the motor winding 8, GTO 1, and off transistor 12 is equivalent to the circuit shown in FIG. 2a.

GTO10 has an anode 10a, an N gate 10b,
The motor winding 8 is connected to the cathode 10d, and the gate resistor 15 is connected between the P gate 10c and the cathode 10d. The collector and emitter of the off transistor 16 are connected between the P gate 10c and the ground potential line 4, and the turn-off pulse signal generation circuit 17 is connected between the base and the ground potential line 4.
A description of the turn-on control circuit connected to the N gate 10b of GTO 1 is omitted, and this circuit is equivalent to the circuit shown in FIG. 2b.

The turn-off pulse signal generation circuit 17 controls the turn-off transistor 16 by referring to the magnitude of the current detected by the current detection resistor 11, and thus controls the turn-off transistor 16.
Controls on/off of 0. The freewheeling diode 18 is connected in parallel with the series circuit of the motor winding 8, the GTO 9, and the current detection resistor 11, and the series circuit of the freewheeling diode 19 and the zener diode 20 is connected in parallel with the series circuit of the GTO 10 and the motor winding 8. Ru.

In the above configuration, current control of the motor winding 8 is performed by keeping the GTO 9 in an on state and controlling the GTO 10 on and off. At this time, the turn-off pulse signal generation circuit 17 refers to the detection signal obtained from the current detection resistor 11 and controls the GTO 10 via the transistor 16 so that the current flowing through the motor winding 8 becomes a predetermined value.

When the GTO 10 is turned off, the current due to the voltage induced by the electromagnetic energy stored in the motor winding 8 flows to the low voltage side terminal 8 of the motor winding 8.
a → GTO9 → current detection resistor 11 → ground potential wire 4
→ Freewheeling diode 18 → Flows through high voltage side terminal 8b of motor winding 8. When the two GTOs 9 and 10 are both turned off, the current due to the electromagnetic energy stored in the motor winding 8 flows from the low voltage side terminal 8a of the motor winding 8 to the freewheeling diode 19 to the zener diode 20 to the power source 3 to the ground potential. It flows through the line 4 → the freewheeling diode 18 → the high voltage side terminal 8b of the motor winding 8.

Here, GTO9 is on and GTO10
Explains the behavior when transitions from on to off state. At this time, the turn-off pulse signal generation circuit 17 generates a turn-off pulse signal to turn on the off transistor 16, and turns on the P of the GTO 10.
Current is extracted from gate 10c. When the GTO 10 is completely turned off, the current due to the electromagnetic energy stored in the motor winding 8 is
9, the current detection resistor 7, and the free-wheeling diode 18, the forward voltage of the free-wheeling diode 18 is
V _BE , the potential of the cathode 10d of the GTO 10 becomes -V _BE with respect to the ground potential line 4. This voltage is transmitted to the collector of the off transistor 16 through the gate resistor 15 and two shunts of the PN junction between the P gate 10c and the cathode 10d of the GTO 10. When the turn-off pulse signal is applied to the base of the off-transistor 16, when the forward voltage -V _BE is applied to the collector of the off-transistor 16, the off-transistor 16
operates as a reverse transistor, and current flows from the emitter to the collector. This current is GTO
10, the GTO 10 attempts to shift to the on state. However, when the GTO 10 shifts to the on state, the potential of the cathode 10d increases in the positive direction, so the off transistor 16 starts drawing current from the P gate 10c again, so the GTO1
0 cannot be in the on state. In the end, the off transistor 16 operates as a reverse transistor.
When current flows into the P gate 10c of the GTO 10, since the GTO 10 operates as an NPN transistor with the N gate 10b as the collector,
A current due to the NPN transistor action of the GTO 10 flows through the motor winding 8, resulting in unnecessary power consumption.

Note that when the GTO 9 shifts to the OFF state, there is no such drop in cathode potential, so such a problem does not occur.

[Problem that the invention seeks to solve]

As described above, the conventional GTO drive circuit turns on the P-gate of the GTO, which has an inductive load connected to its cathode, and the off transistor connected to the ground potential line, and draws current from the P-gate. When turning off the GTO, the operation of the off transistor and the GTO becomes unstable due to the influence of induced voltage due to electromagnetic energy stored in the inductive load, causing unnecessary current to flow through the load.

Therefore, an object of the present invention is to eliminate the unstable operation of the off-transistor and GTO as described above, and to enable accurate and high-speed control of load current.

[Means for solving problems]

To achieve this object, the present invention provides a drive circuit for a gate turn-off thyristor in which an OFF transistor circuit for drawing current is connected to the turn-off gate of a gate turn-off thyristor whose cathode is connected to an inductive load. , a first off transistor connected between the turn-off gate and a ground potential line;
a second OFF transistor connected between the turn-off gate and the cathode; a turn-off pulse signal generating circuit; and applying a turn-off pulse signal generated by the turn-off pulse signal generating circuit to the base of the first OFF transistor; a circuit element such as a low-voltage diode that turns on a first off transistor when the cathode potential of the gate turn-off thyristor is high; The device is characterized in that it includes a Schottky barrier diode that turns on the second off transistor when the cathode potential of the device is lowered.

[Effect]

When attempting to turn off the gate turn-off thyristor that is in the on state, the cathode potential of the gate turn-off thyristor is at a potential approximately equal to the voltage of the power supply. Therefore, when a turn-off pulse signal is generated from the turn-off pulse signal generation circuit, the turn-off pulse signal is at a much lower level than the voltage of the power supply, so the base and emitter of the second off transistor are reverse biased. Reverse bias is blocked and protected by a shot key barrier diode. On the other hand, the first
Since the emitter potential of the off transistor is at the ground potential, its base and emitter are forward biased and turn on, and this first off transistor draws current from the turn-off gate, and the gate turn-off thyristor begins transitioning to the off state. As the transition of the gate turn-off thyristor to the off state progresses, the potential of the cathode decreases, and eventually the cathode potential drops below the ground potential, the first off transistor operates as a reverse transistor, and the gate turn-off thyristor operates as an NPN transistor. try to work.

However, when the cathode potential drops to a predetermined value, the second off transistor turns on, so the current drawn from the turn-off gate continues to flow toward the cathode, which has a lower potential, and eventually the gate turn-off thyristor is completely turned off.

Note that the shot key barrier diode is PN
Compared to a junction diode, a Schottky barrier diode has a lower forward voltage drop and can operate at high speed. , compared to the case where a PN junction diode is used, the number of circuit elements such as low-voltage diodes connected to the first OFF transistor is reduced, and the operation of the second OFF transistor is faster, making it possible to use a gate turn-off thyristor. turn-off occurs at high speed.

〔Example〕

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

FIG. 1 is a driving circuit diagram of a GTO according to the present invention. GTO 21 consisting of an anode 21a, an N gate 21b, a P gate 21c and a cathode 21d
, the anode 21a is connected to the positive electrode of the power source 3,
A motor winding 8 is connected between the cathode 21d and the ground potential line 4, and a free wheel diode 22 is connected in parallel to the motor winding 8. 23 is a first OFF transistor whose collector is connected to the P gate 21c and whose emitter is connected to the ground potential line 4. 24
is a second off transistor, the collector is connected to the P gate 21c, and the emitter is connected to the cathode 21c.
d, and the gate resistor 25 is connected to the P gate 21c.
and the cathode 21d. One end of the output terminal of the turn-off pulse signal generation circuit 26 is connected to the ground potential line 4, and the other end is connected to the low voltage diode 2.
7 in the forward direction, and connected to the base of the first off transistor 23, and connected to the base of the second off transistor 24, with a high voltage shot key barrier diode 28 interposed in the forward direction. Ru. This turn-off pulse signal generation circuit 26 generates a turn-off pulse signal of a logic level much lower than the voltage V _CC of the power supply 3.

Note that a description of the turn-on control circuit will be omitted.

In the above configuration, turn-off control of the GTO 21 will be explained. GTO2 in on state
1 is turned off by the turn-off pulse signal generation circuit 26 generating a turn-off pulse signal. When GTO21 is in the on state,
The potential of the cathode 21d of the GTO 21 is approximately equal to the voltage V _CC of the power supply 3, and the cathode potential decreases from this potential when transitioning to the off state.

As described above, the turn-off pulse signal generated from the turn-off pulse signal generation circuit 26 connected to the base circuits of the first and second off transistors 23 and 24 has a logic level far lower than the voltage V _CC of the power supply 3. Therefore, the base-emitter junction of the second OFF transistor 24 becomes reverse biased, but this reverse bias is cut off and protected by the high voltage shot key barrier diode 28. However, the first off transistor 23
Since the emitter of the transistor 23 is at ground potential, the base and emitter of this transistor 23 are forward biased and turned on, and the P gate 21 of the GTO 21
Draw the current from c. As a result, when the GTO 21 shifts to the OFF state and the cathode potential V _K decreases to the following equation (6), the first OFF transistor 23 becomes OFF state and the second OFF transistor 24
turns on.

V _K = V _F27 + V _BE23 −V _F28 −V _BE24 …(6) Here, V _F27 ; Forward voltage drop of the low-voltage diode 27; V _BE23 ; Forward voltage between the base and emitter of the first OFF transistor 23 drop, V _F28 ; high voltage shot key barrier diode 28
The forward voltage drop between the base and the emitter of the second OFF transistor 24 is, V _BE24 .

Here, V _F27 V _BE23 V _BE24 ≡V _BE 0.7(v),
Since it can be considered that V _F28 0.3 (v), V _K 0.4 (v) ...(7), and in the region where the cathode potential V _K is larger than the value of equation (7), the current path by the turn-off pulse signal is turned off. The first path consists of the pulse signal generation circuit 26 → low voltage diode 27 → the base of the first off transistor 23 → its emitter → the ground potential line 4 → the turn-off pulse signal generation circuit 26, and the cathode potential V _K is (7) The current path in the region smaller than the value of the formula is as follows: turn-off pulse signal generation circuit 26 → high-voltage shot key barrier diode 28 → base of second OFF transistor 24 → emitter → motor winding 8 → ground potential wire 4 → A second path includes a turn-off pulse signal generation circuit 26. That is, in the region of V _K > V _BE 24, the first
The second off transistor 23 is in the active state, the second off transistor 24 is in the off state, and the GTO 21
The turn-off of progresses by the current drawing operation by the first off transistor 23, and V _K < V _BE
In the region 24, the first OFF transistor 23 is in the OFF state and the second OFF transistor 24 is in the saturated state from the active state, so the turn-off of the GTO 21 is caused by the current drawing operation by the second OFF transistor 24. It progresses. GTO21
The change in the cathode potential V _K occurs as the GTO 21 shifts from the on state to the off state, and the on/off switching of the first and second off transistors 23 and 24 also occurs in both off transistors 23 and 24.
This is done automatically by the difference in the junction voltage of the base circuit.

When the GTO 21 is completely turned off, the current due to the electromagnetic energy stored in the motor winding 8 flows back through the freewheeling diode 22, and the cathode potential _VK becomes a negative potential with respect to the ground potential line 4.
However, since the turn-off pulse signal current flows through the second current path and does not flow through the first current path, the first off transistor 23 does not operate as a reverse transistor. The collector of the second off transistor 24 is the GTO 21.
Since the emitter is connected to the cathode 21d, the cathode potential is
Even if V _K becomes a negative potential, V _C 24 > V _E 24 (8) where, V _C 24: Collector potential of the second off transistor 24 V _E 24: Emitter potential of the second off transistor 24 Because of the potential, the second off transistor 24 does not act as a reverse transistor.

FIG. 4 shows another embodiment of the GTO drive circuit according to the present invention. In this embodiment, a Darlington transistor 29 is connected to the first off transistor 23 so that the GTO 21 can be turned off even in response to a large anode current _IA , thereby increasing the current drawing ability. Since the base-emitter junction of Darlington transistor 29 is equivalent to the junction of low voltage diode 27 in the previous embodiment, the low voltage diode is omitted in this embodiment.

Transistors 30 and 31 constitute a turn-on control circuit, and transistor 30 has a voltage of 5 (V).
The turn-off pulse signal is inverted and amplified and applied to the base of the transistor 31. The collector of transistor 31 is
It is connected to the N gate 21b of the GTO 21, and its emitter is connected to the ground potential line 4 to draw current from the N gate 21b and turn on the GTO 21.

In this embodiment, the GTO 21 is driven to be turned on when the turn-off pulse signal generated from the turn-off pulse signal generating circuit 26 is at a low level, and is driven to be turned off when it is at a high level.

In this embodiment as well, as in the previous embodiment, current is extracted from the P gate 21c by the first OFF transistor 23 or the second OFF transistor 24 depending on the cathode potential _VK of the GTO 21. GTO21 can be turned off.

Note that in the description of the two embodiments described above, description of the GTO and current detection resistor between the motor winding 8 and the ground potential wire 4 was omitted, but they are added as necessary, as in the conventional case.

Of course, the present invention can also be applied to things other than current control of motor windings.

〔Effect of the invention〕

As described above, the present invention selects the first off transistor connected between the turn-off gate and the ground potential line of the GTO and the second off transistor connected between the turn-off gate and the cathode depending on the cathode potential. Since the GTO is turned on automatically and draws current, the GTO can be stably turned off even if the cathode potential becomes negative with respect to the ground potential. In addition, in order to cut the reverse bias applied to the base and emitter of the second OFF transistor, we used a shot key barrier diode, which has a lower forward voltage drop than a PN junction diode and can operate at high speed. , compared to the case where a PN junction diode is used, the number of circuit elements such as low-voltage diodes connected to the first off transistor can be reduced, and the operation of the second off transistor is faster, and the gate The turn-off thyristor can be turned off at high speed.

[Brief explanation of the drawing]

Figures 1 and 4 each constitute the present invention.
GTO drive circuit diagrams FIGS. 2a and 2b and 3 are conventional GTO drive circuit diagrams. 3...Power supply, 8...Motor winding, 21...
GTO, 23...first off transistor, 2
4... Second OFF transistor, 26... Turn-off pulse signal generation circuit, 27... Low voltage diode, 28... High voltage shot key barrier diode.

Claims (1)

[Scope of Claims] 1. In a drive circuit for a gate turn-off thyristor in which an OFF transistor circuit for drawing current is connected to the turn-off gate of a gate turn-off thyristor whose cathode is connected to an inductive load, the OFF transistor circuit is connected to the turn-off gate. a first off transistor connected between the turn-off gate and the cathode, and a second off transistor connected between the turn-off gate and the cathode;
A turn-off pulse signal generation circuit and a turn-off pulse signal generated by the turn-off pulse signal generation circuit are applied to the base of the first off transistor to turn off the first off transistor when the cathode potential of the gate turn-off thyristor is high. a circuit element to be turned on; and a shot key barrier diode which applies the turn-off pulse signal to the base of the second off-transistor and turns on the second off-transistor when the cathode potential of the gate turn-off thyristor is lowered. A drive circuit for a gate turn-off thyristor, comprising: 2. The drive circuit for a gate turn-off thyristor according to claim 1, wherein the circuit element is a low voltage diode. 3. The drive circuit for a gate turn-off thyristor according to claim 1, wherein the circuit element is a Darlington transistor.