BS170 Transistor

[Markkim]

Utilizing a microprocessor to regulate the gate, I'm using a BS170 Transistor to turn on/off a sequence of LEDs. My transistor appears to have stopped working because it never turns off. Is this a sign that the transistor has blown?

[dyarker]

Yes, or what ever drives the gate never goes low.
A schematic with values is needed to help more.

From the little you've said, you could have melted to transistor to a lump (internally) of always conductive silicon. We have no way of knowing.

The "magic" in electronics is in the numbers and a bit of algebra.

Cheers,

[haklesup]

Probably shorted the Drain to Source. If so then there is probably current leakage into the gate since that often damages the gate oxide. you could have blown the gate by ESD zap or damaged the channel from overcurrent, its only rated to 500mA continuous and LED in strings can often need more than that. There should be plenty of higher current substitutions if you want to try, use the parameter search on Digikey for example

To test this, its easier if removed from the circuit but the gate should look like an open circuit in both positive and negative directions so if current flows, its definitely bad. It is an enhancement mode FET so with the gate connected to the source, the FET should be off and you should get no current flowing from Drain to Source.

Many FET can be bench tested by measuring resistance from Drain to Source (ID) and tapping the gate to either the red or black probe momentarily can put enough charge onto the gate to turn it on or off.

If you have access to a curve tracer, even an oscilloscope based one, you can test it directly but not many people have a curve tracer available.