help from NE555 experts

Attached is schematic of single push on/off involving a 555 ic to act as a switch for a set of LED day running light. I think the schematic is complete because it was taken from a pcb layout of the actual switch.
As it stand , the light are not coming ON at ignition ON , I need to press the SW for this, so I bridged the SW and the LED are coming on on power up of the circuit.
But for some reason the DRL are tuning off after 30 to 40 min.
Is it because I bridged the SW , is there a better solution to modify the circuit to switch the DRL on at power up ?

Thanks

If you wish for the FET to come on, on power up, then a simple solution woud be to invert the output of the 555. Can be done with a transistor (bipolar) or logic inverters.

Pin 7 is an open collector output which is 'low' when the output is low. You could add a PNP transistor to that, with a base resistor and pull up, and simply connect that 10Mohm resistor to that. Its not ideal as you're adding 4 extra parts, but it'll work.

If you don't want the switch function at all, and jsut want it to 'come on permenantly' when you appliy power, just disconnect the 10M resistors to the FET's gate, and connect it to the V+ line (pin 8, or 4 of the 555). Pretty much makes the entire circuit pointless though.

I've editted out other idea's because I jsut thought of something simple. Add a capacitor, say 10n, to 100nF across R2. From ground to Pin 2/6. The rationale for this is that, upon power up, the only things connected to the trigger/threshold pins are two resistors, setting the voltage at VCC/2. The 555 probably defaults to 'output low' when neither its internal SR flipflops set/reset inputs are triggered. However, with a small capacitor across R2, on power up, this cap brings the treshold voltage below VCC/2, triggering the 555, and turning it on.

As for its effect on 'normal' operation, I'm fairly sure, as long as the caps value is small (<47nF say) it shouldn't adversly affect the switches operation, and only server to trigger the output on powerup. Good luck!

So you want the LED on (ergo, the FET on) as soon as power is applied? - assuming it is powered by the ignition line, andnot the battery directly). But do you still want to use the switch function? Both the ideas in my previous post will work depending on what you want. Either tie the 10k (R3) resistor to V+ for permenantly on, or a capacitor across R2 (100k resistor btw). As R2 is 100k, and not 53K as previously stated, you *may* have issues using the switch (night take longer for the state to change, so you'll have to hold down the switch for a second), but it would always 'turn on' on power up.

All the best.

I Blueteeth,

No , I do not want to use the SW ,I will go for the option of connecting R3 direct to V+ powered by the ignition line.
Thanks for your help