EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: connectTek on May 03, 2020, 12:31:18 pm
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I need to switch a 24vdc LED strip at 1amp.
The switch is a Reed switch, I can only find a Reed that is off when no magnet is near, therefore I have the MosFet on when magnet is away,( door open).
Would any problems arise from this CCT?.
I have tested it on work bench and very rarely the MosFet is left very slightly on, drawing approx 50ma, this happens very rarely, if some one can help me understand why it would be much appreciated.
Cheers
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Yes, that circuit should work.
The only things I can think of which would cause the MOSFET to be slightly on, when the switch is closed, are:
- A loose connection to the switch.
- The contacts not making due to oxide deposits on the contacts, not being broken due to the low current.
Check the connections to the switch, if they're good, then it's #2. Some switches require a certain wetting current to work. Try adding a 100nF capacitor in parallel with R1, to provide a current spike to the switch contacts. I do think it's more likely to be #1 because most reed relays are hermetically sealed and filled with an inert gas, so oxidation shouldn't be a problem.
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Cheers and thanks for reply