During the operation of the thyristor T, the anode A and the cathode K are connected to the power supply and the load, and the main circuit of the thyristor is formed. The gate pole G of the thyristor and the cathode K are connected to the control thyristor, and the control circuit of the thyristor is formed.
The operating conditions of the thyristor:
1. When the thyristor is subjected to the positive anode voltage, the thyristor will only turn on only when the gate voltage is positive. The thyristor is in a positive conduction state, which is the thyristor thyristor characteristics, called controllability.
2. In the case of a thyristor, if there is a certain positive anode voltage, no matter how the gate voltage is, the thyristor is kept on, that is, after the thyristor is connected, the gate will lose its function. The gate only is the triggers.
3. When thyristor is turned on, when the main circuit voltage (or current) is reduced to zero, the thyristor is turned off.
4. When the thyristor is subjected to reverse anode voltage, the thyristor is in a reverse blocking state, no matter what voltage the gate electrode takes.
In the intermediate frequency furnace, the closing time of the rectifier side is less than KP-60 microsecond, and the KK-30 side of the inverter side is closed for a short time. This is the main difference between the KP tube and the KK tube. During the operation of the thyristor T, the anode A and the cathode K are connected to the power supply and the load, and the main circuit of the thyristor is formed. The gate pole G of the thyristor and the cathode K are connected to the control thyristor, and the control circuit of the thyristor is formed.
From the internal analysis process of thyristor, the thyristor is a four layer and three terminal device, which has three PN junctions of J1, J2 and J3. Figure 1, the NP in the middle can be divided into two parts, forming a PNP transistor and a NPN transistor. Fig. 2, when the thyristor is subjected to the positive anode voltage, the thyristor copper guide must be blocked from the negative voltage PN junction J2. The collector current of each transistor at the same time is the base current of the other transistor.
Therefore, two composite transistor circuits, when a sufficient gate current Ig inflows, will form a strong positive feedback, which leads to the saturation conduction of the two transistors and the transistor saturation conduction. It is assumed that the collector current of the PNP tube and the NPN tube is corresponding to Ic1 and Ic2; the emitter current is Ia and Ik; the current amplification coefficient is a1=Ic1/Ia and a2=Ic2/Ik, assuming that the reverse leakage current of the flow over the J2 junction is Ic0, the anode current of the thyristor is equal to the sum of the collector current and the total leakage current of the two tubes: Ia=Ic1 Ic2 If the gate current of Ik Ic0 is Ig and the cathode current of the thyristor is Ik=Ia Ig, it can be found that the anode current of the thyristor is: I= (Ic0 Iga2) / (1- (A1 A2)) (1 - 1) (1- (A1 A2)) and the corresponding current amplification coefficient of silicon PNP tubes and silicon tubes and the changes in the emitter current of the thyristor, as shown in Figure 3.
When the thyristor is subjected to positive anode voltage, and the gate is not subjected to the voltage, the Ig=0 (A1 A2) is very small in the type (1 - 1), so the anode current of the thyristor is in the forward blocking state of the Ia Ic0 thyristor. At the positive anode voltage, the thyristor flows from the gate G to the current Ig. As the large enough Ig flows through the emission junction of the NPN tube, the starting current amplification coefficient A2 is increased, and the large electrode current Ic2 flows through the emission junction of the PNP tube, and the current amplification coefficient A1 of the PNP tube is increased, and the larger electrode current Ic1 flows through the NPN tube. The emitter junction. Such a strong positive feedback process is carried out quickly.
When the A1 and A2 are increased with the emitter current and (A1 A2) 1, the denominator 1- (A1 A2) 0 in the type (1 - 1), thus the anode current of the thyristor is improved, and the current of the thyristor is completely determined by the voltage and circuit resistance of the main circuit. The thyristor is in the forward state. In the type (1 - 1), after the thyristor is opened, 1- (A1 A2) 0, even if the gate current is Ig=0, the thyristor can still keep the original anode current Ia and continue to pass.
When the thyristor is connected, the gate has lost its function. When the thyristor is turned on, if the voltage of the power supply is continuously reduced or the circuit resistance is increased, the anode current Ia is reduced to the maintenance current of less than IH, as A1 and A1 decrease rapidly, when 1- (A1 A2) is 0, the thyristor will recover the blocking state.
