Author Topic: Issue in low side mosfet based switch  (Read 891 times)

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Offline abhishekkumar1902Topic starter

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Issue in low side mosfet based switch
« on: February 12, 2020, 09:46:51 am »
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?
 

Offline EEEnthusiast

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Re: Issue in low side mosfet based switch
« Reply #1 on: February 12, 2020, 10:01:05 am »
How do you cut off the power to the unit?
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https://www.zscircuits.in/
 

Offline abhishekkumar1902Topic starter

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Re: Issue in low side mosfet based switch
« Reply #2 on: February 12, 2020, 10:08:47 am »
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.
 

Offline exe

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Re: Issue in low side mosfet based switch
« Reply #3 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.
 

Offline Vovk_Z

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Re: Issue in low side mosfet based switch
« Reply #4 on: February 12, 2020, 01:13:26 pm »
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.
+1 to previous questions. Because it is strange - if there is no power - nothing can turn horn on.
 

Offline DBecker

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Re: Issue in low side mosfet based switch
« Reply #5 on: February 12, 2020, 01:28:22 pm »
That seems a very complex circuit to control a horn.

What is special about the signal input level that it needs to be isolated?  Is there anything special about the horn?

Why not use a standard automotive low-side or high-side clamping driver, with much less complexity?  Why did you an extra stage rather than having the optocoupler to directly pull up the gate?
 

Offline Wimberleytech

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Re: Issue in low side mosfet based switch
« Reply #6 on: February 12, 2020, 03:31:07 pm »
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.

In order to troubleshoot this strange behavior, you must draw the COMPLETE circuit to understand sneak paths.  What you have drawn is only part of the circuit and what you have additionally described is, at best, slightly helpful.

Please show everything.
 
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Offline EEEnthusiast

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Re: Issue in low side mosfet based switch
« Reply #7 on: February 12, 2020, 06:25:17 pm »
Just use a relay, as is done in automotive world.
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