I was a silent reader for a long time and could solve all the problems on my own, but this problem is really freaking me out. I was messing around until 3 AM today with this "feature" and still don't know what is going on...
There is a LED strip, that is blinking with 1.5 Hz (50% on time) and +12 V. I have to create a circuit, that can be placed between voltage source and the LED strip that delays the blinking by a few hundred milliseconds. It does not have to stop blinking these hundred milliseconds later, delaying the on time is enough. Interrupting the ground connection is no option, because there are a few more more LED stripts that share the same ground potential.
My current circuit
Due to the fact that my LED strip is connected to ground and I have to delay the incoming +VCC signal, I think (am I right!?) the easiest way is to use a P channel MOSFET as high side switch. I know that I could use a N channel MOSFET with a bootstrap driver, but i read a lot of articles that say using a P channel MOSFET is just fine, if you don't care about the higher Rdson (I am switching ~200 mA, so i don't really care about Rdson). In addition my PCB space is limited and a DIP8 driver would not fit well (Whole pcb should be designed as through hole).
The gate signal for the MOSFET is coming from the output pin of a NE555, which threshold and trigger pin is connected between a resistor and a capacitor.
I have really strange things going on with my circuit. For test purposes, I connect a single LED with a resistor to VCC, to test the functionality, but I just cant get the expected result. First, my circuit was working a little bit, the led blinking was delayed for the expected time, but went on for a few milliseconds when +VCC was applied to the circuit. I think the reason for this is, that the MOSFET is conductive by default, and my NE555 needs a little time to turning the mosfet off.
The other, much stranger problem is that after a few blinking cycles the LED is on the whole time!? First, it is glowing just a bit but then starts flickering/changing its brightness...
I have attached my current circuit. I would be so happy if somone could tell me what I messed up with this circuit design.
Or if there are much better solutions (maybe attiny13 as gate control!?) I would appreciate every recomendation.
Thank you in advance!! And sorry for my bad english :X