Re: External Mosfet boards actually quite good!
June 06, 2020 12:21PM
Worth bearing in mind John, but maybe simple transistor circuit to just raise the 3.3v to 5v? Or a boost converter?


Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions
Re: External Mosfet boards actually quite good!
June 06, 2020 02:38PM
Quote
DjDemonD
So I was using a mechanical relay for my 24v heated bed on my corexy which has a second power supply.

So I bought one of these external mosfet boards and wired it up.
...

I like these (your first one) as well. The only issue I had with them is the signal goes through a wull-wave bridge then into an opto-isolator, but the current limit resistor in the path to the opto's LED is high enough in value (560 ohms) that a 3.3v signal from a 32-bit board, not going through one of the board's existing mosfets) won't let enough current through to fully turn on the opto's output phototransistor. A simple component swap for a 300 ohm resistor (remember, there's two diode drops going through that bridge rect) makes it usable with 3.3V logic, as long as that pin can deliver 15mA when driven low.

Edited 2 time(s). Last edit at 06/06/2020 02:47PM by wallaceowen.
Re: External Mosfet boards actually quite good!
June 06, 2020 02:51PM
Quote
DaveOB
Thank You DjDemonD

Only just ordered the module so will take a while to arrive.

Thanks for the guidance and the ideas.

I suppose if the module does not work with a 5V signal, we could always beef up the signal with a transistor, or something like a 4N25 opto, controlled by 5V from the output pin, and connect the 12V PSU to the Mosfet Module Input.

Just change the opto isolator's current limit resistor. You should see a surface mount component betwwn the signal pins and the inputs to the opto isolator. Drop it's value down and 3.3V will drive it fine. Drop it so the opto LED gets 15mA so the opto's output turns the power MOSFET on full.
Re: External Mosfet boards actually quite good!
June 06, 2020 03:20PM
DUPLICATE

Edited 2 time(s). Last edit at 06/06/2020 03:21PM by DjDemonD.


Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions
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