Re: DC relay latching voltage

john larkin <jlarkin_highland_tech> wrote:

On Sat, 24 Aug 2024 11:11:19 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
 

Pimpom <Pimpom@invalid.invalid> wrote:
[...]

Normal power supply decay will not release the relay quickly enough. So
I've added a section that turns the 12V relay off when the decaying PS
drops below 7.5V. Works fine in simulation.
 
However, due to interaction with other sections, the gate voltage of the
transistor driving the relay rises again briefly to about 2.5V before
the shutdown process is complete. But by this time, the 12V supply has
dropped to less than 3V.

 
Add a few diode drops in the supply to the Base of the transistor and a
pull-down resistor from Base to Earth.  You could even use a 7.5v Zener
so the transistor switched directly off the PS and no other active
components were needed.

 
A 2-resistor voltage divider can reduce mosfet gate swing.
 
Or an R-C in his case of a transient gate drive spike.
 
Or both.
 
 

If the C is gate to drain (or base to collector) then the miller effect
slows rate of flux collapse enough to remove need for any additional
components across the coil.


--
piglet