Fig. 3: Circuit Diagram showing Zero Volt Drop across MOSFET in Reverse Bias
3. If the value of drain to source resistance (Rds(off)) comes out to be zero or less than that specified in its datasheet, the MOSFET is defective
3. Take an ohmmeter and check the drain to source resistance, Rds(on). This time the reading should be very low (zero or approximately zero) than the previous Rds(off) reading (as shown in figure below). This will confirm that the MOSFET is in good condition. Refer to the datasheet of the MOSFET in case to check the value of drain to source resistance in on condition, Rds(on) and compare it with the observed value. If the observed value has much variation with that specified by the datasheet, the MOSFET is faulty.
In the next tutorial, bootstrap circuit for driving the high side MOSFET will be discussed.