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you need something in between to translate from 5v to 12v.
You mean, in the circuit i draw, i need something more so the P-channel mosfet can do its job ?
No your FET circuit works, the voltage translation is the reason that 2 FETs are needed to make the high-side switch, which was your original question.
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it worked fine many times. Once it didnt ...
What do you mean ?
Once it ignited before it was supposed to - YouTube
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your overall system better have an independent fail-safe that meets integrity required for your hazard level.
... Are you talking about security..... Do you think about something different to protect the system ?
No, talking about unintended function of software in safety critical systems. Read the story of Therac 25 Therac-25 - Wikipedia Do not depend on software alone, no matter what encryption.
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You could save a FET by just putting the igniter in place of the second 10K resistor,I simply don't understand how the igniter could be fire at this place .
because when N FET turns on the drain goes to ground, the top end of resistor or igniter is at +12V.
We are worried that your diagram does not show any independent mechanical interlock as a safety backup for software.