I'm currently encountering difficulties in testing my MOSFETs.

I am in the process of designing a snubber for an IRF840 operating at 20kHz.

Upon attempting to test (drive) the MOSFET, at <= 50% duty, in its basic state without any additional circuitry, I observed a 4V voltage drop from the 12V drain voltage and a current draw of approximately 150mA, resulting in significant heat generation.

This situation is perplexing to me because I did not anticipate any current to be drawn, especially not at such a high level.

I conducted the same test with another MOSFET from the same batch, and the results were consistent.

Could someone please assist me in comprehending this phenomenon?

 

You need to supply an accurate Schematic of your testing-setup,
including accurate labeling of all components.
.
.
.

 

You need to supply an accurate Schematic of your testing-setup,
including accurate labeling of all components.
.
.
.

Thanks for your time.

I've included a quick sketch as an image below. I've also tried adding a 10k resistor between the gate and source but it still acts the same.

 

You are shorting the power supply with the MOSFET - huge currents flow.

 

Hi,
You must have a Load resistor in the Drain, you are shorting out your power supply.

E

Sensa, beat me too it.

 

You are shorting the power supply with the MOSFET - huge currents flow.

It acts same way even when the driver output is low (without being driven)

 

Hi,
You must have a Load resistor in the Drain, you are shorting out your power supply.

E

Sensa, beat me too it.

Thanks.

I'll try that!

 

It acts same way even when the driver output is low (without being driven)

Aha! Not driven is not low! The gate is a capacitor and will maintain whatever charge is on it when it is not driven high or low. You need either a push-pull driver (recommended) or a resistor from gate to source (good at lower frequencies.)

 

What is the <<Basic state>>?? If with Gate disconnecting then Mosfet acts laike it must do by definition, ie burn down.

 

You need to supply an accurate Schematic of your testing-setup,
including accurate labeling of all components.
.
.
.