How to use a multimeter to detect the quality of field effect tubes?
Due to the presence of a damping diode between the D-S poles of commonly used MOSFETs, the performance of MOSFETs can be determined by using the diode level of a digital multimeter to detect the diode voltage drop between the D-S poles. The detailed detection method is as follows.
Turn the gear switch of the digital multimeter to the diode mode, connect the red probe to the S pole and the black probe to the D pole. At this time, the screen of the multimeter will display the voltage drop value of the diode between the D-S poles. The voltage drop value of high-power field-effect transistors is usually between 0.4 and 0.8V (mostly around 0.6V); There should be no voltage drop between the black probe connected to the S pole, the red probe connected to the D pole, and the G pole and other pins (for example, in an N-channel field-effect transistor, a P-channel field-effect transistor should have a voltage drop value when the red probe is connected to the D pole and the black probe is connected to the S pole). On the contrary, it indicates that the field-effect transistor has been damaged.
Field effect transistors are usually damaged by breakdown, and in this case, the pins are usually in a short-circuit state. Therefore, the voltage drop value between the pins should also be OV. After each measurement of MOS field-effect transistor, a small amount of charge will be charged on the G-S junction capacitor, establishing a voltage UGS. When measuring again, the probe may not move (if using a digital multimeter, the measurement error will be large). At this time, short circuit the G-S terminals briefly.
The damage of field-effect transistors is usually caused by breakdown and short circuit. At this time, measuring with a multimeter, the pins are usually interconnected. After the field-effect transistor is damaged, there is generally no obvious appearance damage. For severely overcurrent damaged field-effect transistors, it may explode.
