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On by default switch

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kuon:
I have a power supply which has an inhibit pin that must either be left floating for the power supply to be on, or pulled down for the power supply to be off.

I want the power supply to be off by default when power is applied and be turned on when a control line is pulled high.

So basically, when the control line is low, the circuit must conduct, and when the control line is high it must be open circuit and let it float.

I would usually use a transistor with a pull up resistor, but the documentation of my power supply clearly state that the inhibit pin must not be pulled up.

Do you have recommendation on how to implement this?

oPossum:
Normally closed (Form B) optocoupler

For example... https://www.mouser.com/datasheet/2/240/CPC1106N-1548424.pdf

kuon:
Thanks, didn't think of the optocoupler approach. Will do perfectly.

NiHaoMike:

--- Quote from: kuon on August 29, 2019, 07:39:48 am ---So basically, when the control line is low, the circuit must conduct, and when the control line is high it must be open circuit and let it float.

I would usually use a transistor with a pull up resistor, but the documentation of my power supply clearly state that the inhibit pin must not be pulled up.

--- End quote ---
Transistor without a pullup resistor.

David Hess:
A p-channel JFET or p-channel depletion mode MOSFET if you can find one will do that.

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