12V High Side Switch

StarMan

Does anyone know of a switch that I can put on the high side of a load (the low side is not accessible) that I can·operate with an SX?· The switch will be normally closed and needs to be opened only intermittently for a short·time (2-3 seconds).· The current could be in excess of 15 amps, 20 amps max.

I looked at Crydom and they only have one relay that looks like it will work but it's almost $30.· And besides, I would really prefer to have this switch be small and mounted on a PCB with the SX.

I tried a logic level mosfet (FDP7030BL) but it doesn't seem to work.

Any ideas?

Mike Green

Best bet is to use an power relay using a switching transistor to supply the coil current. DigiKey has a variety of these for $2-4 that'll switch 16A at up to 125VAC. Here's one example:

Post Edited (Mike Green) : 6/13/2008 6:00:13 AM GMT

LoopyByteloose

Your choices are either a Solid State relay or a traditional relay. Both will work and much depends on your wear and tear from the duty cycle. Odd as it may seem, the traditional coil relays seem to come in smaller footprint with lower costs. And the traditional relay usually fails in an OFF mode. Thus preventing a runaway ON condition.

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···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

StarMan

OK.· Thanks for the suggestions.· I'll order one and give it a try.

Chris I.

Phil Pilgrim (PhiPi)

The MOSFET you tried is an N-channel device, typically used for low-side switching. To make it switch 12V on the high side, you would have to raise the gate voltage to 12V, plus the V_GS level required to turn it "on". There are voltage-boosting MOSFET gate drivers that can do this. The LTC1154 is one example.

-Phil