lingling wrote on May 30th, 2017, 12:27am:
I have built many timer circuits like the following picture shows but the only problem Iíve ran across is the supply voltage/current,3 to 18 volts,if current exceeds 1.5 amps it will smoke the 555 timer,it has happened to me several times and i havenít solved this problem.
The 555 delivers the base current for the 2n3055.
Given the base resistor, the possible base current times 12V times a
duty of 50%, should be more than enough to thermally overload
the IC. Add an emitter follower or something?
Another problem could be the primary of the transformer -- there
will be a large leakage inductance and subsequently a nasty spike
when the 2n3055 attempts to turn off. Maybe this spike reaches
the IC pins and drives them below ground?