Ron H said:
Your zener will never conduct unless your supply goes above about 13.4V. If it does, either Q3, or the zener, or both will overheat and possibly fail.
What about my other comment?
Why do you need push-pull emitter followers? Are you using a CMOS 555? A bipolar 555 will source and sink over 200mA, IIRC.
Ron, the main problem is that my mosfets are not
turning off.
Well, the main purpose of the push-pull is to "pull down" the mosfet gate when no tension or low level is applied to Q5 base.
I think that a transistor conducting to the ground do a better job than a "pull down" resistor.
Well, the circuit is working "nice" now, look what I've done a few hours ago:
I connected the circuit in a tweeter with an ammeter, I've notice that it were flowing about 0.5A of current and Q2 (IRF740) were getting a little bit hot.
I removed it (letting Q1 only) and changed Q4 (PNP one).
The circuit worked fine, but when a spark, from the ignition coil HT terminal, leaked and hit the negative terminal...the remaining mosfet were destroyed.
Well, I have to discover what caused the Q2 to fail, with an ohmmeter I measured the resistance between all the terminals (G-S, G-D, D-S...), for my surprise it was about 50 ohms (!!!).
Q2 gate were leaking causing Q1 to conduct as well, causing malfunction in the whole circuit, and probably that was the cause of Q4 burning as well.
But I have no idea what caused Q2 to fail, maybe the it was first affected by the coil back-emf (this is my only guess).
Later I'll try to add some zener or varistor between the drains and sources to protect the mosts against back-emf.