DC biasing point, power MOSFET ? - UK Vintage Radio Repair and Restoration Discussion Forum

Al (astral highway) · 3rd Feb 2017, 10:33 am

Confusion; I've seen a circuit from a reputable source which shows an IRF840 with a DC bias voltage of 0.8V set by a voltage divider/ zener diode and potentiometer. This is below the threshold voltage (min 2V to 4V). I had thought that the correct bias for linear operation was the midpoint between the drain voltage and the threshold voltage ...the circuit describes a drain current of 100mA on standby.

So, mystery. The device I am using is an IXFH16N50P, which has similar characteristics. I want it to be a linear amplifier at RF, around 1.5MHz, as part of a home brew bit of kit to accurately test the attributes of a physically very large inductor - if you're interested!! The drain voltage will be low, 30V. I don't need advice around the configuration of the amplifier except for the DC bias point, please.

Many thanks !!!

3rd Feb 2017, 10:33 am	#1
Al (astral highway) Dekatron Join Date: Nov 2006 Location: London, UK. Posts: 3,496	DC biasing point, power MOSFET ? Confusion; I've seen a circuit from a reputable source which shows an IRF840 with a DC bias voltage of 0.8V set by a voltage divider/ zener diode and potentiometer. This is below the threshold voltage (min 2V to 4V). I had thought that the correct bias for linear operation was the midpoint between the drain voltage and the threshold voltage ...the circuit describes a drain current of 100mA on standby. So, mystery. The device I am using is an IXFH16N50P, which has similar characteristics. I want it to be a linear amplifier at RF, around 1.5MHz, as part of a home brew bit of kit to accurately test the attributes of a physically very large inductor - if you're interested!! The drain voltage will be low, 30V. I don't need advice around the configuration of the amplifier except for the DC bias point, please. Many thanks !!! __________________ Al Last edited by Al (astral highway); 3rd Feb 2017 at 10:46 am.