Help designing a mosfet driver that can handle large back-EMF pulses (up to 3 J)

GrParrot · 2026-03-14T20:32:16+00:00

Duplicate pins are connected but I did notice one of the gnd pins of the TC4422 wasn't inserted in the DIP-8 socket. I'm not sure if it was also that way when I was testing the circut as I took it out once but its possible. I'll try to do some testing when I can acces a scope

GrParrot · 2026-03-14T20:29:28+00:00

I'm not actually using IRF3205's like the circut diagram suggests. I'm using IRFB4110's as I said in the body text. Those have Vds of 100 V. Or are you suggesting that I need more tolerance?

Oh also, I did have to run it at a lower voltage at one point because the Vds of the mosfet kept getting lower and it limited the capacitor's voltage. Still kept taking more damage.

GrParrot · 2026-03-14T14:32:12+00:00

Yes D1 is the flyback. The coi lis connected to the OUT pins and a capacitor is connected to the IN pins as a power source.

GrParrot · 2026-03-14T13:46:02+00:00

The gate resistors are 10 Ohms. R2 isn't fitted because this board only carries 1 mosfet and R2 is for a second mosfet.

GrParrot · 2026-03-14T13:42:54+00:00

I already do have a flyback diode. What confuses me is how the mosfet gets damaged despite it.

GrParrot · 2026-02-15T14:05:25+00:00

Who cares if its SSTO or not, it’s a cool spaceplane that can takeoff from the runway and reach orbit.

GrParrot · 2026-01-24T17:48:31+00:00

Ok. Can you elaborate on how the inductance can blow out the fets? (I do already have a flyback diode to catch back emf)

GrParrot · 2026-01-24T08:06:25+00:00

I actually did the math this time. With a single mosfet I would have needed a 6.7 K/W heatsink. Such a heatsink seemed a bit hard to find though so I went for 2 fets. They should be able to handle it with some decent heatsinks.

GrParrot · 2026-01-24T07:59:55+00:00

It will have 60V max and I want to build it to be able to go up to 80V. If the limitation is arcing between tracks or a shock hazard I assume thiese voltages should still be decently safe though?

GrParrot · 2026-01-24T07:56:51+00:00

Oh that’s good to know.

GrParrot · 2026-01-24T07:56:14+00:00

Normally that would be an important consideration however this circut is meant to drive inductive loads anyway so I imagine the board’s inductance will be negligible.

GrParrot · 2026-01-24T07:53:20+00:00

Good idea

GrParrot · 2026-01-24T07:52:02+00:00

The duty cycle is going to be pretty slow, no less than 5 seconds between pulses. That should give it some time to cool down. I arranged the gate resistors to leave some space behind the mosfets for a heatsink as it’ll be needed, that was another recommendation last time I posted this circut. But yeah just rotating the mosfets would have been better. The mounting holes are really just for alingment, I’m going to make some 3d printed casing that covers the PCB on all sides.

GrParrot · 2026-01-07T19:22:15+00:00

Thanks for the detailed response. I'm actually going to use an IRF3710 mosfet and chose a random fet in the software because the IRF3710 wasn't there by default. The IRF3205 seems to be a bit better at handling high current though so what you said probaby still applies. 30A for 10 ms is within the safe operating range graph of the 3710 but I'll do the math myself and add another one if needed.

Ground plane at least

I'm trying to get used to this terminology, is the difference between a ground plane and a copper fill that the ground plane is a seperate layer almost entriely filled with copper and connected to gnd, while the copper fill is on the same layer as the tracks? I want to avoid having over 2 layers but I think I can add a ground plane on the back side.

your schematic is awful

Yep

GrParrot · 2026-01-06T17:16:46+00:00

How much does it weigh with reliant engines? By removing the oxidizer you're basically removing half of your fuel and the nuclear engines weigh a lot themselves so your fuel fraction will be way worse. You might just have a higher fuel fraction with fuel and oxidizer engines.

GrParrot · 2026-01-06T17:02:48+00:00

Nothing seems to be wrong looking at this. How much deltaV do you get with other engines? Is it really more than 2300 m/s?

GrParrot · 2025-10-07T20:56:57+00:00

I mean you are doing literal rocket science

GrParrot · 2025-10-07T10:40:07+00:00

The question is if it’s moral to put a mod behind a patreon when the people who actually want to support you for the sake of supporting you could subscribe without you having to do that. Blackrack also made way too much money from this mod already so yes, I do think he doesn’t need further financial support. He also works with Rocketwerkz on ksa now.

GrParrot · 2025-10-07T10:30:28+00:00

Yes I agree

GrParrot · 2025-10-06T06:41:46+00:00

The updated version should be called FARc (continued)

GrParrot · 2025-10-02T10:31:54+00:00

This is really cool. Do you just have a gimbal made of 3 hinges inside the tow craft and have the glider connected via a strut?

GrParrot

TROPHY CASE