1 and 2 are correlated: the 2Megs. Reading indicates that there is a leakage
path from gate to ground. The charge impressed on the gate leaks through it
and causes a gradual turn off of the transistor, hence the increasing
internal resistance of the FET.
You can test a FET on a curve tracer, but you won't get a lot of information
as compared to a relatively low current sweep. On the other hand you're
going to need one hell of a power supply!
Alex 4Z5KS
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Dan Sawyer
Sent: Monday, February 23, 2009 5:59 AM
To: Amps
Subject: [Amps] testing RF power MOSFET devices
This is a general question regarding 'testing' RF power MOSFETs
1. There appears to be a difference between the MRF150 and the ST
equivalent based on the 'simple' test of placing the negative lead of an
Ohm meter on the source and the positive on the gate and then the drain.
A set of 4 MRF devices show a steady low reading while a set of 4 ST
devices discharge over a few seconds and the resistance rises. Is this
significant?
2. Another pair of ST devices show a couple of meg Ohms resistance
across drain and shorted gate-source. These devices perform well in a
curve tracer, full voltage but limited current.
3. Is there a way to test a MOSFET at near full load with a curve
tracer? (this would require temporary mounting of the device on a heat
sink.)
Thanks - Dan
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