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In this Video we try to explain with this video an easy way to verify if they are good or broken.
We think to do this tutorial because the LDMOS are Efficient, Robust but Complex Devices and even the simplest of operations like testing a good mosfet from a bad one is never an easy task especially for the beginners in the field.
Typically the LDMOS, very robust from the part of the Drain are more weak on the Gate side.
A fast way to know is it is defective is measuring the ohmic resistance between: Source and Gate and between: Source and Drain.
The resistive value must be high, very high (several MOhm or infinite) . On the other side, when the LDMOS is broken this value change really significantly e becomes of few KOm or even few Ohm.
Because the LDMOS are paired inside, it's always possible to compare both sides of it.
Many times, one half of them is broken while the other half is good.
The best way to do this meassure is to unmount the LDMOS, but good results can be achieved measuring it with the complete RF Amplifier.
In this case, the values are highly affected by the components on the circuit but, if one half of the LDMOS is really in short circuit it's easy to find the difference with the half good one.