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How to judge the quality of thyristor ?
As one of the most frequently used basic components in circuit design, the quality of thyristor is directly related to the operation safety of the whole system. Therefore, engineers are required to judge the performance and quality of thyristor before design.
To judge whether a controllable silicon component is in good condition, engineers need to check it from four aspects.
First, it is judged that the three PN junctions of the element should be in good condition.
Secondly, when the voltage between the cathode and the anode is inversely connected, it can block the non-conduction.
Thirdly, when the control pole is open, the voltage between the anode and the cathode is not conductive when the voltage between the anode and the cathode is forward connected.
Fourthly, when the positive current is added to the control pole and the positive voltage is applied to the cathode and anode, the thyristor should be turned on, and the current of the control pole should be removed and still in the on state. Thyristor elements satisfying the above four conditions can meet the requirements of design and use.
It is very simple to see whether a thyristor element meets the above requirements. The first three aspects can be judged by measuring the interelectrode resistance of thyristor with the ohmic shield of a multimeter. The specific operation method is to measure the positive and negative resistances between the cathode and the anode by using R *1k or R *10k blockade (the control pole is not connected to the voltage). These two resistances should be very large. The larger the resistance value is, the smaller the forward and reverse leakage current is. If the measured resistance value is very low or nearly infinite, it indicates that thyristor has broken through short circuit or opened circuit, and this thyristor can not be used.
Next, we need to check whether the PN junction between the control pole and the cathode is damaged. We can measure the resistance between the anode and the control pole with R * 1K or R * 10K block of the multimeter. The forward and reverse resistance values should be more than several hundred kiloohms. If the resistance value is very small, it indicates that the thyristor breaks down the short circuit. The positive and reverse resistance of PN junction between control pole and cathode is measured at R *1k or R *100 block. If the positive resistance is close to zero or infinite, it indicates that the PN junction between control pole and cathode has been damaged. The reverse resistance should be large, but not infinite. Normally, the reverse resistance is obviously larger than the forward resistance.
If you want to judge whether thyristor has been damaged by breakdown, engineers can use multimeter to select resistance R * 1 block, then connect black pen to anode, and red pen to cathode. At this time, the multimeter pointer should not move. The red-meter pen is connected to the cathode and the black-meter pen is connected to the control pole instantaneously with the tip of the pen while the anode is not removed. At this time, the multimeter resistance indicator should be deflected to the right, and the resistance reading is about 10 ohms. If the anode is connected with the black pen and the cathode is connected with the red pen, the pointer of the multimeter deflects, which indicates that the one-way thyristor has been broken down and damaged.