Thyristor also involves the problem of triode, so many designers can not accurately identify the middle pole of thyristor at the initial stage. In fact, this problem can be solved smoothly as long as the multimeter is used. In this paper, we will introduce the method of using multimeter to quickly distinguish the three poles of thyristor.
1: Discrimination of single and bidirectional thyristors
Measure any two poles first, if both the positive and negative measuring pointers do not move (R × Gear 1), which may be a, K or G, a pole (for unidirectional thyristor) or T2, T1 or T2, G pole (for bidirectional thyristor). If one measurement indicates tens to hundreds of ohms, it must be unidirectional thyristor. The red pen is connected to pole K, the black pen is connected to pole g, and the rest is pole a. If both the forward and reverse test instructions are tens to hundreds of ohms, it must be a bidirectional thyristor. Then turn the knob to R × 1 or R × For the retest of gear 10, there must be a slightly larger resistance value, then the slightly larger red pen is connected to pole g, the black pen is connected to pole T1, and the rest is pole T2.
The method to quickly identify the three poles of thyristor, that is, the pins, is very simple. According to the principle of p-n junction, just use a multimeter to measure the resistance value between the three poles. The forward and reverse resistance between anode and cathode is more than several hundred kiloohms, and the forward and reverse resistance between anode and control electrode is more than several hundred kiloohms (there are two p-n junctions between them, and the directions are opposite, so the forward and reverse of anode and control electrode are not connected).
There is a p-n junction between the control electrode and the cathode, so its forward resistance is about several to hundreds of ohms, and the reverse resistance is larger than the forward resistance. However, the characteristics of the control electrode diode are not ideal. The reverse is not completely blocked, and a relatively large current can pass through. Therefore, sometimes the measured reverse resistance of the control electrode is relatively small, which does not mean that the characteristics of the control electrode are not good. In addition, when measuring the positive and negative resistance of the control pole, the multimeter should be placed in gear r*10 or r*1 to prevent the reverse breakdown of the control pole with high voltage.
If the positive and negative polarity of the measured element is short circuited, or the anode and control electrode are short circuited, or the control electrode and cathode are short circuited in reverse, or the control electrode and cathode are open circuited, the element is damaged.
Thyristors are divided into unidirectional thyristors and bidirectional thyristors, both of which have three electrodes. Unidirectional thyristor has cathode (k), anode (a) and control electrode (g). Bidirectional thyristor is equivalent to two single thyristors in reverse parallel. That is, one unidirectional silicon anode is connected with the other cathode, and its lead out end is called T2 pole. One unidirectional silicon cathode is connected with the other anode, and its lead out end is called T2 pole. The rest is the control pole (g).