场效应管和电源IC好坏的判断（Field effect tube and power IC are good or bad judgment）.doc

场效应管和电源IC好坏的判断（Field effect tube and power IC are good or bad judgment） FET and power IC good or bad judgment, from left to right is generally G, D, S, generally only 3 feet. The middle foot D is not an empty foot, and is connected with its heat dissipation. The G is used as the trigger pin. When the power is controlled, the D is used as the power input pin, and the S is the output. How simple it is measured by numbers table block diode red pen is connected to G, the black pen is connected with the D release, with a red pen is connected with the D, a black pen is connected to S, then to measure D, S has a certain guide with resistance, conduction, probably a few to a few hundred ohm. Mechanical watch X1 block is more obvious. Then contact the 3 feet of the field tube with your finger, then D, S, (red pen, D, black pen, S), the end of infinity, the reverse is very small resistance. As mentioned above, the NPN type VMOS field tube. Power IC to measure whether it has control pulse output (using oscilloscope testing), power supply, working conditions are normal, and so on. The substitution method is best. I. main parameters of field effect transistors (1) DC parameter The saturation drain current IDSS may be defined as the corresponding drain current when the voltage between the gate and source is equal to zero and the voltage between the drain and source is greater than the clamping voltage. Pinch off voltage UP, which can be defined as the UGS required to reduce the ID to a small current when the UDS is constant Switch on voltage UT, which can be defined as the UGS required to make ID reach a certain value when the UDS is constant (2) AC parameter Low frequency transconductance GM, which describes the gate and source voltage control over drain current. The capacitance between three electrodes of a MOSFET, the smaller the value, the better the performance of the tube. (3) limit parameter Drain and source breakdown voltage. When the drain current rises sharply, the aval