JPH0646230Y2 - Current limit circuit - Google Patents

Description

[Detailed Description of the Device] A. Field of Industrial Application This device relates to a current limiting circuit at turn-off of a GTO thyristor.

B. Overview of the device This device is a current limit circuit at turn-off provided in the gate circuit of a GTO thyristor, which uses a resistor to determine the peak value of the off-gate current that flows in the overdrive capacitor provided in the gate circuit of the GTO thyristor. By limiting the size, the overdrive capacitor can be downsized.

C. Conventional Technology FIG. 3 is a circuit diagram showing a gate circuit of a conventional GTO thyristor, 1 is a GTO thyristor, and a cathode electrode 2 of this GTO thyristor 1 is connected in series with a turn-on power source 3 and a turn-off power source 4. Is connected to the common connection point 5. The positive electrode of the turn-on power supply 3 is connected to one end of an overdrive capacitor 7 via a first electronic switch 6 composed of a transistor or FET. The other end of this capacitor 7 is connected to the gate electrode 8 of the GTO thyristor 1. A diode 9 having the illustrated polarity and a resistor 10 are connected to both ends of the capacitor 7. The negative electrode of the turn-off power source 4 is connected to the first electronic switch 6 and the capacitor 7 via the second electronic switch 11.
Is connected to a common connection point 12 with. Reference numeral 13 is a capacitor connected between the positive and negative electrodes of the turn-off power supply 4.

Next, to explain the operation of FIG. 3, in order to turn on and off the GTO thyristor 1, it is necessary to flow a gate current having the waveform shown in FIG. 4 in the GTO thyristor 1. Here, FIG. 4 will be described. In FIG. 4, the gate current waveform in the ON period of the GTO thyristor 1 starts to flow when the time t ₁ is reached, and becomes a pulsed current with a fast rising peak value at the time t _2. Become. A constant value of current flows through the GTO thyristor even during the on period after the GTO thyristor is turned on. Further, in order to turn off the GTO thyristor 1 in the ON state, it is necessary to flow a reverse current through the gate. According to the gate current waveform shown in FIG. 4, a reverse current starts to flow at time t ₃ and the GTO thyristor 1 is turned off by the steeply rising pulse current reaching the peak value at time t ₄ .

The gate current shown in FIG. 4 is supplied from the turn-on power supply 3 and the turn-off power supply 4 to the GTO thyristor 1. First, in order to turn on the GTO thyristor 1, the first electronic switch 6 is turned on. As a result, the gate-on current flows through the power supply 3 → first electronic switch 6 → capacitor 7 or resistor 10 → gate electrode 8 → cathode electrode 2. Normally, the capacitor 7 is discharged at the start of turn-on of the GTO thyristor 1, and most of the gate current at the time of turn-on flows through the capacitor 7, resulting in a pulse-shaped current waveform as shown in FIG. After that, when the capacitor 6 is charged, the gate current will flow through the resistor 10.

Next, in order to turn off the GTO thyristor 1, an off gate current is passed as follows. That is, the off-gate current flows through the capacitor 13, the cathode current 2, the gate current 8, the capacitor 7 or the resistor 10, and the second electronic switch 11. However, at the start of turn-off, the capacitor 7 is charged as shown in the figure, so that the off-gate current flows through the capacitor 7. After that, when the capacitor 7 is completely discharged, the off-gate current is changed to the diode 9
To flow through.

D. Problems to be solved by the device As described above, a large gate current flows through the capacitor 7 at the start of turn-on and turn-off. Where the third
The peak value of the off-gate current in the conventional example shown in the figure will be obtained and viewed. The rise of the off-gate current shown in FIG.
Assuming that the capacity of the capacitor 7 is C (Farad), the off-gate current is 1/2 ▲ kt ₀ ² ▼ = C (V
_It flows through the capacitor 7 until the time t ₀ shown in FIG. 5, which is determined by ₁ + V ₂ ). Note that V ₁ is a forward voltage drop voltage of the diode 9, and V ₂ is a voltage obtained by subtracting the voltage drop (on-time) voltage of the first electronic switch 6 and the GTO thyristor 1 from the voltage of the turn-on power supply 3. The peak value of the current i ₂ flowing through the capacitor 7 is given by the following equation.

In addition to V ₁ = 0.5 V, V ₂ = 5 V in the above formula (1), C
= 10 μF, k = 150 A / μS, the peak value of the current
The i ₂ can reach almost 130 amps. Therefore, there is a problem that the capacitor 7 becomes large in size in order to withstand the large current flow.

The above GTO thyristor 1 is not so large in capacity, but GTO
When the thyristor 1 has a large capacity, in order to shorten the turn-off time, the voltage of the turn-off power supply 4 is increased (about 10 times that of the turn-on power supply 3) to increase the rise of the off-gate current. However, if the voltage of the turn-off power supply 4 is increased in this way, the peak value and the effective value of the current flowing through the capacitor 7 at the time of turn-off also increase. For this reason, there is a problem that the shape of the capacitor 7 becomes large similarly to the above.

E. Means for Solving Problems This invention is a GTO thyristor off-gate current supply circuit G
A resistor is inserted in the current path between the gate of the TO thyristor and the electronic switch to limit the current flowing through the overdrive capacitor.

F. Action The peak value and effective value of the current that flows in the overdrive capacitor when the GTO thyristor is turned off is reduced by the resistance inserted in the off-gate current path.

G. Embodiment An embodiment of the present invention will be described below with reference to the drawings, in which the same parts as those in FIG. 3 are denoted by the same reference numerals.

In FIG. 1, reference numeral 14 is a resistor, and this resistor 14 is inserted in an electric line 15 connecting a common connection point 12 of the first electronic switch 6 and the capacitor 7 and the second electronic switch 11. The cathode of the diode 9 is connected to the electric line 15. The diode 9
The anode of is connected to the gate electrode 8.

When the resistor 14 is provided as described above, the off-gate current when turning off the GTO thyristor 1 is capacitor 13 → cathode electrode 2 → gate electrode 8 → capacitor 7 → resistor 14 →
It flows through the path of the second electronic switch 11. Therefore, the off-gate current is limited by the resistor 14, and the peak value and effective value of the current flowing into the capacitor 7 can be reduced. After the capacitor 7 is discharged, a current flows through the diode 9.

The peak value of the current when the resistor 14 is provided in the off-gate current path as described above is given by the following equation.

i ₁ = (V ₂ + V ₁ ) / R (2) Note that R is the value (ohm) of the resistor 14, and V ₁ and V ₂ are the same voltages as described above.

In the above formula (2), for example, R = 0.5 ohm, V ₁ = 0.5 volt,
Substituting V ₂ = 5 volts, i ₁ = 5.5 / 0.5 = 11 amps. This current peak value i ₁ is about 1/10 of that of the conventional example.
Therefore, the capacitor 7 can be sufficiently configured with a small shape.

The value of the resistor 14 has a condition that the electric charge of the capacitor 7 must be sufficiently discharged while the GTO thyristor 1 is off. That is, _assuming that the minimum off period of the GTO thyristor 1 is τ _s , the value R of the resistor 14 is set so as to satisfy the following equation.

R << τ _s / C (3) FIG. 2 is a circuit diagram showing another embodiment of the present invention, in which a capacitor 7 and a resistor 14 are connected in series, and a diode 9 and a resistor 10 are connected in this series circuit. They are connected in parallel.

In each of the above embodiments, when the GTO thyristor 1 has a large capacity, the peak value and the effective value of the current flowing in the capacitor 7 can be suppressed even when the voltage of the turn-off power supply 4 is increased. Can be miniaturized.

H. Effect of the Invention As described above, according to this invention, since the resistor is inserted in the off-gate current path, it is possible to reduce the peak value and effective value of the current flowing through the overdrive capacitor, which has a large rise in the off-gate current. As a result, the size of the capacitor can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, FIG. 3 is a circuit diagram showing a conventional example, and FIG. 4 is a gate of a GTO thyristor. A current waveform diagram and FIG. 5 are explanatory diagrams showing an off-gate current. 1 ... GTO thyristor, 3 ... turn-on power supply, 4 ...
… Turn-off power supply, 6,11 …… First and second electronic switches,
7 ... Capacitor for overdrive, 9 ... Diode, 10,14 ... Resistance, 13 ... Capacitor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-112873 (JP, A) Actually opened 58-95191 (JP, U) Actually opened 57-127586 (JP, U)

Claims (1)

[Scope of utility model registration request] 1. A turn-on power supply and a turn-off power supply are connected in series, a common connection point thereof is connected to a cathode of a GTO thyristor, and a positive electrode of the turn-on power supply is connected to a series circuit of a first electronic switch and an overdrive capacitor. Through
It is connected to the gate of a GTO thyristor, and a resistor for conducting a gate current after completion of capacitor charging and a diode for conducting an off-gate current after completion of capacitor discharging are connected in parallel at both ends of the capacitor, and the first electronic switch and In a gate circuit of a GTO thyristor in which a second electronic switch is inserted in a circuit between a common connection point of a series circuit with a capacitor and a negative electrode of a power supply for turn-off, a common connection point of a series circuit of the first electronic switch and a capacitor A resistor for limiting an off-gate current is provided between the cathodes of the diodes, the off-gate current is caused to flow through the second electronic switch, and the off-gate current after completion of capacitor discharge is caused to flow through the diode to the second electronic switch. Current limiting circuit.