What value resistor, and how do I use it to test the gate?
Do you know what DC volts I can use to check if the FET's gate is working or not? I don't want to damage the FET
Hello,
Well since the FET has a high input impedance you should easily get it to work with a 100k or even 1 meg resistor on the gate in a static test.
As others have indicated, depending on what kind of device you are testing the test results could be quite different. That's because the FET's and MOSFET's have a wide variety of specifications that you need to review before testing the device so you know what to look for.
For example, for a normal FET you might see 500 ohms across drain to source when it is turned on, but for a power MOSFET you could see much less than 1 ohm like 0.050 ohms even, but then other MOSFET's might show 10 ohms but they are still good because they have different specifications.
In general regular FET's would be tested at lower current levels than power MOSFET's.
To find out the min and max gate voltage, you really do have to look at the data sheet for that particular device part number. There's no other way because here we see a wide variation too from maybe 5v up to 20v or something like that, and if you apply 20v to a 5v part it might blow out, and if you apply 5v to a 20v device it might not turn on fully. So you have to know what you are dealing with before you begin any tests.
Also as audioguru pointed out, you need to test the device out of circuit for best results. If you intend to test in circuit then you need a schematic of the entire circuit so you know what to look for during the test.
When you use a DC power supply to test you dont need an ohm meter. You can use a resistor on the output as load and test that way. It will usually be much better that way.
Because there are so many variations here your best bet is to review the data sheet first and if you still cant come up with something then you'll just have to ask here for more help for each device. If you only have a few devices you want to test that wont be too hard.