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Depletion mode achieved!

A project log for enhancement to depletion

DIY method to lower gate threshold voltage of regular MOSFETs, ultimately reversing it.

DeepSOICDeepSOIC 10/18/2016 at 21:240 Comments

In previous project log, I promised to crank up the torture voltage to see, what happens. Sorry for delay, I was too busy repairing active stylus of my notebook, because I needed it fixed desperately.

I planned to raise the voltage to about -45 volts. So I raised it slowly, till at about 43 volts I noticed significant current was leaking through gate. I lowered the voltage to -42.5 volts, and noticed that the mosfet is already in depletion mode! It happened very quickly. The gate threshold voltage was about -0.46 V. AWESOME!!!!

But drain current at zero gate voltage was still quite low. So I decided to push it into depletion even further. I applied -42.5V again, and in about 20 seconds I was measuring gate threshold voltage of about -1.8 V. Now, I get 1.3 A through that test LED when shorting gate to source. Now that's something!

As the transistor was changing so fast, I didn't have time to gather the data for plotting. Sorry, no graph this time, oops =)

I hope to make a video with another DeepSPICE setup demonstrating the transistor in action, as a torch brightness regulator. Stay tuned.

I also want to measure the transfer characteristic of the MOSFET. From the current at 0V vs negative Vgt, it is obvious the transistor's amplification (transconductance) has dramatically dropped. I want to see how much.

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