Experimenting with MOSFETS: Total Gate Charge

RE: Experimenting with MOSFETS: Total Gate Charge

maxjack123 — Tue, 15 Oct 2024 09:36:52 GMT

Hi, jc2048 , Very interesting experiment on your page. I have a few queries, I understand that you are using the MOSFET on the high side to limit the current. My queries are (a) will there be a chance of a short circuit if the pulse width of the DUT is too high? (b) If I change the DUT from IRF730 to super junction mosfet or SiC, will this circuit still work for measuring the charge?

Thanking you

Best regards

Manish

RE: Experimenting with MOSFETS: Total Gate Charge

ellen86119 — Mon, 27 Nov 2023 10:05:48 GMT

I used the same method as you for the current source, but my current source was a little slow to respond.

It takes 20us to reach the 5mA I set.

JFET(LSK170B)

RE: Experimenting with MOSFETS: Total Gate Charge

genebren — Fri, 02 Aug 2019 14:51:23 GMT

Very cool experiment/demonstration. It is nice when thing go well, as seen in this setup.

RE: Experimenting with MOSFETS: Total Gate Charge

dougw — Fri, 02 Aug 2019 14:02:02 GMT

Very nicely done...cool experiment.

When I saw the title, I though oh ya they do have some weird characteristic. I don't normally think too much about such things, but I find them interesting. I'm glad Jon explores them.

RE: Experimenting with MOSFETS: Total Gate Charge

jc2048 — Fri, 02 Aug 2019 13:59:17 GMT

Although I didn't mention it in the blog above, when I first tried the experiment I got something wrong. Without

thinking too much about what I was doing, I added a gate resistor of 100 ohms in series with the gate of the

constant-current MOSFET. Here's the effect it had. The blue trace is Vgs of the DUT and the yellow trace is the current

probe (the scale is 1V per amp). The probe is measuring the drain current of the constant-current MOSFET between

the drain and the decoupling on the pcb. With the gate resistor, the current leaps up to 8A before the constant-

current MOSFET finally gets it under control when the drain voltage of the DUT stops moving.

[View:/resized-image/__size/480x234/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-cd1c4b2d-7063-4966-80b3-30aebf1801ab/contentimage_5F00_207763.png:480:234]

Without the gate resistor, the current increases nicely to 2A and just sits there [the current probe only has a bandwidth of

5MHz, so the ramp up may be as much to do with the probe risetime as the way the MOSFETs turn on].

[View:/resized-image/__size/480x234/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-cd1c4b2d-7063-4966-80b3-30aebf1801ab/contentimage_5F00_207764.png:480:234]

RE: Experimenting with MOSFETS: Total Gate Charge

colporteur — Fri, 02 Aug 2019 12:27:26 GMT

Nice work.

Sean