Electronics > Beginners

Issue in low side mosfet based switch

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abhishekkumar1902:
I have designed this opticaly isolated low side switch (schematic attached in the post) for driving the HORN of my car through some arduino electronics. It works flawlessley except when I turn OFF the power supply to this circuit. When I shut off the power suppy to this circuit, I notice the load (horn) switches ON for a very very short time say 100ms. Why is this happening?

EEEnthusiast:
How do you cut off the power to the unit?

abhishekkumar1902:
Arduino circuit and and this circuit both are connected to the vehicle's battery through the ignition switch. The horn rings for very short time say 100ms when I turn off the ignition key, even when the arduino didn't  turned ON the MOSFET previously. The only difference is arduino side has an additional 4700uF capacitor in the EMI filter design.

exe:
Can it be Arduino is sending a signal just before switch off? It's easy to verify, disconnect signal lines and see if the problem still persists.

Vovk_Z:

--- Quote from: exe on February 12, 2020, 10:24:50 am ---Can it be Arduino is sending a signal just before switch off? It's easy to verify, disconnect signal lines and see if the problem still persists.

--- End quote ---
+1 to previous questions. Because it is strange - if there is no power - nothing can turn horn on.

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