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3842 problem low volt

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What do you suppose your VIN-(ICC*150K) leaves for the
C2 voltage maximum? Datasheet says 1mA max / 0.5 typ
so if you want your 10V UVLO minimum, your VIN had
better be more than 85V on a good day, 160V on a bad
day.
 

Audioguru said:
Why do you think it will work without the Mosfet?
Does your car drive fast without its engine?
Click to expand...

thank you but the 3842 must work first to drive the mosfet

What do you suppose your VIN-(ICC*150K) leaves for the
C2 voltage maximum? Datasheet says 1mA max / 0.5 typ
so if you want your 10V UVLO minimum, your VIN had
better be more than 85V on a good day, 160V on a bad
day.
Click to expand...

but i think it need more than 1mA .with 150k it give me 2.8 only
now the mosfet is useless because 3842 not work with 2.8v
 
Last edited:

You didn't yet tell which input voltage has been used in your test. The suggested startup resistor value in 3842 datasheet is 56K for 115 VAC.

If you provide sufficient startup current > 1 mA but Vcc doesn't raise up to the 16V UVLO threshold, it should be easy to determine where the current flows. Either a defective 3842 or a different circuit problem.
 

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