JPH0318374B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an off-gate pulse amplification circuit suitable for a gate turn-off thyristor.

[Technical background of the invention and its problems] An off-gate pulse as shown in FIG. 1 is used to turn off a gate turn-off thyristor.

Conventionally, as an example of an off-gate pulse amplification circuit that generates such pulses, the circuit shown in FIG. 2 is often used. In Figure 2, 1 is a DC power supply, 2 is a capacitor, 3 is a resistor, 4 is a pulse transformer, 5 is the primary winding of the pulse transformer 4, 6 is the secondary winding, 7 is a transistor, and 8 is a pulse A gate turn-off thyristor (hereinafter simply referred to as a GTO) is supplied with an off-gate pulse via a transformer 4.
) gate circuit (hereinafter simply referred to as load),
9 is a Zener diode, and 10 is a diode.

When the transistor 7 is turned on, the voltage E of the DC power supply 1 is applied to the primary winding 5 of the pulse transformer 4 via the capacitor 2. capacitor 2
is not charged at first, so there is a voltage E in the primary winding 5.
is applied, and a voltage of E/n is generated in the secondary winding 6 (n is the number of primary windings/the number of secondary windings). As capacitor 2 is charged, the voltage applied across primary winding 5 gradually decreases. The steady-state value is E·R2/R1+R2, where R1 is the resistance value of the resistor 3, and R2 is the primary winding equivalent resistance value of the load resistor. Furthermore, as the excitation current of the primary winding 5 of the pulse transformer 4 increases, the voltage drop across the resistor 3 increases, and 1
The voltage applied to the secondary winding 5 decreases.

Next, when the transistor 7 is turned off, the excitation current flowing through the primary winding 5 cannot immediately become zero, so the pulse transformer 4 is excited by the closed circuit of the primary winding 5 → Zener diode 9 → diode 10. The circulating current continues to flow until the energy stored in the inductance becomes zero. The electric charge charged in the capacitor 2 is consumed in the closed circuit of the capacitor 2 and the resistor 3, and becomes zero.

Therefore, the output voltage waveform of the circuit shown in FIG. 2 (load 8
The voltage across the load) is as shown in Fig. 3 (Here, the Zener voltage of the Zener diode 9 is taken as E _D. ) Note that there is no need to consider the voltage in the negative direction because it is cut off by the diode inside the load.

As described above, the off-gate pulse amplification circuit shown in FIG. 2 can produce a waveform almost similar to that shown in FIG. 1, but it has the following drawbacks.

(a) The energy stored in the excitation inductance of the pulse transformer, the energy charged in the capacitor, and the energy consumed in the resistor 3 all become losses.

(b) It is necessary to add a circuit (9 and 10 in Figure 2) that consumes the energy stored in the excitation inductance (if transistor 7 is turned on before the stored energy reaches zero, the stored energy in the pulse transformer will be accumulated). , the core of the pulse transformer becomes saturated and no energy is transferred to the load).

(c) As shown in Figure 3, when the voltage applied to the load is reversed from positive to negative, dv/dt is high, so the load 8
Current may flow in the opposite direction due to the reverse recovery charge of the diode inside. This means that if we apply the circuit shown in Figure 2 to the GTO's off-gate circuit, after turning off the GTO with a peak off-gate current of 200A, if in the opposite direction there is only a 1/1000
Even if a current of 0.2A flows, it is a GTO
turns on, requiring measures such as using a high-speed diode with a very small reverse recovery charge and further strengthening the negative bias (not shown).

In order to solve the above-mentioned drawbacks, Japanese Patent Application Laid-Open No. 136023/1983 proposed an off-gate pulse amplifier circuit which was designed to be smaller and more reliable by reducing losses and reducing the number of components.

FIG. 4 merely shows an example thereof.

In FIG. 4, 11 is a DC power supply, 12 is a diode, 13 is a capacitor, 14 is a pulse transformer, 15 ¹ and 15 ² are primary windings, 16 is a secondary winding,
17 is a transistor, and 18 is a load similar to the load shown in FIG. The operating principle of this circuit is omitted here.

As the capacity of GTO increases (e.g. 2000A class), the off-gate current becomes steeper (e.g. 30~40A/
μsec) rise with a high peak value (e.g.
300A~400A) current is required. To increase the current value, lower the intermediate tap of the primary winding and reduce the number of turns of the primary winding ¹⁵² to increase the voltage appearing in the secondary winding in Figure 4. However, in this case, not only the peak value but also the value of the entire waveform becomes large, and a voltage higher than the Zener voltage (for example, 20 V) between the cathode and gate of the GTO is constantly applied. This results in
If the gate loss not only increases but also exceeds the allowable value due to DC power supply fluctuations, etc.
There is also a risk of destroying the GTO gate, which could damage the reliability of the GTO.

[Object of the Invention] The present invention has been made in view of the above-mentioned points, and provides an off-gate pulse amplification circuit that obtains a higher peak current and higher di/dt as an off-gate current of a GTO, and does not increase gate loss. The purpose is to provide.

[Summary of the Invention] In order to achieve this object, the present invention provides a third winding and a switching element on the primary side of a pulse transformer.

[Embodiment of the Invention] FIG. 5 shows an embodiment of the present invention. In FIG. 5, parts that are the same as those in FIG. 4 and shown with the same symbols have the same functions. That is, FIG. 5 shows the DC power supply 11, the diode 12, the capacitor 13, the pulse transformer 14, and the primary side of the pulse transformer 14.
winding 15 ¹ , second winding 15 ² , third winding 15
³ , the secondary winding 16, and the first transistor 17
and a load 18, a second transistor 19, and diodes 20 ¹ and 20 ² connected in series to transistors 17 and 19, respectively.

Now, the voltage of DC power supply 11 is E, and the voltage of capacitor 13 is
Assuming that the voltage of is E _c , in steady state E _c
>E. Suppose that the number of turns (N1, N2) of the first winding 15 ¹ and the second winding 15 ² are both equal, and the ratio of the number of turns M of the secondary winding 16 is (N1/M) and (N2/M ) is n1, and the number of turns of the third winding 15 ³ is less than the number of turns of the second winding 15 ² (N3), and the ratio (N3/M) to the number of turns M of the secondary winding 16 is n2 ( n2<
n1). When the transistor 19 is turned on now, the voltage between both ends B and D of the primary winding ¹⁵³ is
E _c is applied, and the potential at point A is E _c (1+N1/
N3). Therefore, the diode 12 is reverse biased and there is no inflow from the DC power supply 11. At this time 2
A voltage of E _c /n2 appears in the next winding 16. load 1
Assuming that the resistance value of the capacitor 8 is R ³ and the capacitance of the capacitor 13 is C, the capacitor C starts discharging at a time constant τ1=C·R ³ ·(n2) ² . When the capacitor C is discharging at time t=t1, the transistor 19 is turned off and the transistor 17 is turned on, and at that point the discharge time constant of the capacitor C is switched to C.R.(n1) ² .
Eventually, when the discharge of the capacitor 13 is completed, the voltage across it becomes E/2 (assuming N1=N2), the potential at point A becomes E, and the diode 1
2 is forward biased and conducts.

In this way, the primary winding 15 of the pulse transformer 14
Voltage E is applied to the series circuit of ¹ and 15 ² , and N1
= N2, so the voltage of the secondary winding is E/
It is reduced to 2n1 and becomes a steady value. Diode 20 ¹ and 20
² is provided to prevent reverse pressure from being applied to the other transistor when the transistor is turned on. Figure 6 shows the above process.
This shows the voltage waveform of the next winding.

Next, when the transistor 17 is turned off, an equivalent circuit as shown in FIG. 7 is formed, and the capacitor 13 is recharged. That is, since the primary windings 15 ¹ and 15 ² of the pulse transformer 14 are tightly coupled to each other, the excitation current im flowing through both windings becomes the excitation current 15 ² as the transistor 17 turns off. becomes zero immediately, but the excitation current of ¹⁵¹ becomes 2im and charges the capacitor 13. Determining E _c from Fig. 7, almost all of the excitation energy of the pulse transformer 14 is stored in the capacitor 13, and E _c = 2E
become. At this time, the reverse voltage appearing in the secondary winding 16 of the pulse transformer 14 changes slowly as shown in Figure 6, so the reverse recovery current of the diode in the load 18 is almost zero and only in the forward direction A large current can flow (only in the direction that turns off the GTO).

In the explanation of FIG. 5, it is assumed that the number of turns of the first winding 15 ¹ and the second winding 15 ² are equal, but by changing the turns ratio, the waveform of FIG. 6 applied to the load becomes flat. The voltage E/2n1 of the section can be changed, and the peak value can also be changed independently by changing the turns ratio n2. That is, the peak value and plateau voltage can be changed independently.

FIG. 8 shows an example in which the capacitor is divided into two parts so that the capacitances of the capacitors differ, and the same characteristics as in FIG. 5 can be obtained. Also, the 9th
In the figure, one end of the capacitor 13 is connected to the pulse transformer 1.
4, and the other end is connected to the (+) side of the DC power supply 11. In the example shown in FIG. 10, a diode is connected between the first winding and the second winding of the pulse transformer 14. This is an example in which 12 is inserted. Furthermore, Figure 11
This is an example when a PNP transistor is used.
In addition to transistors, the switching element may be replaced with, for example, an FET, GTO, SCR, and a commutation circuit. Various other design changes are possible without changing the gist of the present invention.

[Effects of the Invention] As described above, according to the present invention, for example, a large-capacity GTO
In order to obtain a current with a steeper rise and higher peak value, such as is required for the off-gate current of the By using a stepped configuration, the peak value and the flat part value of the off-gate pulse can be adjusted independently, so that a steeper large current can be supplied. Furthermore, since the voltage that exceeds the Zener voltage between the cathode and gate of the GTO is for a short period of time, the gate loss will not increase or exceed the allowable gate loss, and the loss of the amplifier circuit will be low. can be provided.

[Brief explanation of drawings]

Fig. 1 is a diagram of the off-gate pulse waveform to be applied to the gate turn-off thyristor, and Fig. 2 is a diagram of a conventional off-gate pulse amplification circuit that obtains the waveform of Fig. 1.
Fig. 3 is an output waveform diagram for explaining the operation of Fig. 2, Fig. 4 is a diagram of an improved pulse amplification circuit that obtains the waveform of Fig. 1, and Fig. 5 is a pulse amplification diagram showing an embodiment of the present invention. The circuit diagram, FIG. 6 is an output waveform diagram for explaining the operation of FIG. 5, FIG. 7 is an equivalent circuit diagram for explaining the operation of FIG. 5, and FIGS. 8 to 11 are each of the present invention. FIG. 7 is a circuit diagram showing another different embodiment. 1, 11...DC power supply, 2, 13, 13 ¹ , 13 ²
... Capacitor, 3... Resistor, 4, 14... Pulse transformer, 5, 15 ¹ , 15 ² , 15 ³ ... Primary winding,
6, 16... Secondary winding, 7, 17, 19... Transistor, 8, 18... Load, 9... Zener diode, 10, 12, 20, 21... Diode.

Claims (1)

[Claims] 1. Three primary windings in which the number of turns of the first winding is N1, the number of turns of the second winding is N2, and the number of turns of the third winding is N3; It has M number of secondary windings, and [(N1+N2)/M]>[N3/M], and N2>
A pulse transformer with the condition N3, a series circuit of the first winding of this pulse transformer and a diode, and a series circuit of the second winding and the first switching element are connected in series and connected to a DC power supply. And the third
A series circuit of the winding and a second switching element is connected in parallel to the series circuit of the second winding and the first switching element, and a series circuit of the first winding and the diode is connected in parallel to the series circuit of the second winding and the first switching element. A capacitor is connected between the connection point between the winding of the pulse transformer and the series circuit of the first switching element and either pole of the DC power supply, and a unidirectional semiconductor element is connected to the secondary winding of the pulse transformer. An off-gate pulse amplification circuit characterized in that it is connected to a gate circuit of a gate turn-off thyristor through a gate to supply an off-gate current. 2 Three primary windings in which the number of turns of the first winding is N1, the number of turns of the second winding is N2, and the number of turns of the third winding is N3, and a secondary winding with the number of turns M. has a line, and [(N1+N2)/M]>[N3/M], and N2>
A pulse transformer with the condition N3, a series circuit of the first winding and the first diode of this pulse transformer, and a series circuit of the second winding, the first switching element, and the second diode are connected in series. A series circuit of the third winding, the second switching element and the third diode is connected to the second winding, the first switching element and the second diode.
A first capacitor is connected in parallel to a series circuit of diodes, a first capacitor is connected in such a way that a discharge path is formed through at least the second winding and the first switching element, and at least the third winding A second capacitor is connected so that a discharge path is formed through a second switching element, and a secondary winding of the pulse transformer is connected to a gate circuit of a gate turn-off thyristor through a unidirectional semiconductor element. An off-gate pulse amplification circuit characterized in that it supplies an off-gate current.