I've just finished building a DIY spotwelder using mosfets and driver chips. You can find the build info here: https://github.com/KaeptnBalu/Arduino_Spot_Welder

(The creator is up to Version 3 but I'm building Version 1)

But I couldn't use some of the components he listed so I swapped out, mainly the mosfets from IRF3704 to IRF1405 - And the driver chips from MCP14E10 to MIC4424 (sorry didn't have enough rep points to post the links)

You can find the schematic here

The drivers are driven by an Arduino, everything is wired correctly as far as I've tested.

What I've found is the driver chips have an output of just under 1v when in the off state, this, of course, saturates the transistors.

I've found that if I put a 10k resistor from pin 5 & 7 from the mosfet controller ground to act as a pull-down resistor the circuit works correctly.

I'm just a little perplexed as to why there would be any output whatsoever, have I missed something in the MIC4424 data sheet that states that it needs a pull-down?

Any thoughts welcome. Thanks.


1 Answer 1


When driving MOSFETS with Micros. It is important (but not often mentioned) to use a pull-down resistor on a NPN type MOSFET (or Pull-up on a PNP type mosfet). To prevent your Gate from floating!

Note that the Gate acts as a small capacitor and stores some charge causing the MOSFET to 'float'. You use the 10K resistor from Gate to Ground as an anchor to ensure the Gate drains to 0v when not being driven.


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