I recently purchased a MOSFET Power Switch Module to react to a +/- 12/24V DC supply to a Garage Door Opener Motor that’s supplied from an H Bridge. (I have installed a locking device which worked on the previous Opener’s normal, 24V DC,) When fed to a normal Relay the H Bridge no longer worked, however the MOSFET at 12V Gate Supply worked perfectly - not so when voltage increased to 24. What size Zener Diode do I need to apply to my (about to be ordered) new MOSFET Power Switch Module?
Hey @Anthony176129,
Looking at the datasheet for the MOSFET present on the Power Switch Module:
The maximum Gate-Source voltage is 20V, hence why your 24V at the gate is not working.
Additionally,
Minimum to activate the FET is just under 3V
Realistically, a Zener Clamp circuit with a voltage ranging anywhere from 3V-20V will work. I would personally stray from the edges of that range slightly. Technically, in a simple zener clamp, a higher-clamped voltage will mean a smaller voltage drop across the resistor, causing decreased power consumption. Something to keep in mind, but a simple resistor value should be fine.
Hi Anthony
About a 12V Zener should be fine. You will need a resistor in series to limit zener current. About 1kΩ up to about 2k2Ω should be OK. You can’t go too high here as you will slow down switching time with the risk of overheating the Mosfet if large currents are drawn.
Be aware that at 1kΩ the zener current will be 10mA which will be there at all times the Mosfet is on.
At 1kΩ the resistor power dissipation will be 100mW and the zener 120mW so 1/4W devices should handle this OK.
Cheers Bob
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Thanks to you both I’ve just now Bench-Tested the new configuration with 100% success. In Situ Test tomorrow but all the Dummy Load/Voltages I used replicated reality. Big upgrade to my very basic knowledge and I’m mightily impressed by your well presented and useful replies. Again, much appreciated. ATB, Tony
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Glad to hear that you got it sorted!
