The resistance of a MOSFET is so high that this reading should be in megaohms. You should obtain a reading indicating an extremely high resistance. Put the multimeter on resistance mode to initiate the test. You can also use an ohmmeter instead of a multimeter to check the drain to source resistance.The polarity of the connection is therefore inconsequential on the outcome of the test. A well-functioning MOSFET should indicate a high drain to source resistance irrespective of the connection of the ohmmeter probes.The following are some of the fundamental steps of conducting the resistance test: This test is also easy and requires only an ohmmeter to perform. The resistance test takes advantage of this property to test if the MOSFET is faulty. When there is no triggering pulse at the MOSFET’s gate terminal, its drain to source resistance is high. If the multimeter indicates any reading different from zero, the device is faulty. The multimeter should not give any reading in this mode since the diode is now in reverse bias. Reverse the probe connections to create an open circuit.If the multimeter shows a reading of zero or no reading, this MOSFET is faulty. While in this mode, the multimeter should indicate a reading between 0.4 V to 0.9 V. In this connection, the body diode is in forwarding bias mode. For the NMOS testing, connect the multimeter’s red probe to the MOSFET source and the black probe to the drain.First, ensure that the multimeter is in diode mode.The following are some of the critical steps of testing the conductivity of a MOSFET via the diode test: A diode that also reads zero on the multimeter is also faulty.įigure 6: A multimeter showing a zero reading A diode that does not read within this range is probably defective. When an NMOS is in reverse bias, the diode operates as a circuit. For most of the MOSFETs, the forward drop is approximately between 0.4V to 0.9V. When the MOSFET is in forwarding bias, the drop experienced across the diode is less in varying degrees. The value that you will obtain depends on the type of diode. In this case, the anode is at the source while the cathode is at the drain. Therefore, in an NMOS, the body diode is usually from the source to the drain. This method requires the assembly of a test circuit to test whether the MOSFET is functioning appropriately.įigure 4: An electric circuit board Method 3:Testing a MOSFET–Using a measuring meterįigure 5: A Measuring Meter Testing a MOSFET–Diode TestĬonducting this test is straightforward as one only needs a multimeter with diode mode. Method 2: Testing a MOSFET–Using electronic components
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