Hi,
I'm building a solid-state flasher relay for my bike as the standard one is load dependant - ie if a bulb is out it flashes at twice the rate. I don't want this as I'm using LED's. I've used a 555 in astable mode.
I've got the cct built up on veroboard at the mo, and am playing with a few transistors. Basically the emitter will be the 'flash' wire so this will be wired to a flylead to connect to the wiring loom. +ve 12V is supplied to the cct upon left or right indication.
My problem is this. If I connect pin 3 to the base of the transistor via a 1K resistor (like I was taught) then it will flash a bunch of leds, but not a 21W bulb.
If I directly connect pin 3 to to base (shorting the resistor) then the bulb WILL flash, but the transistor gets scarily hot very quick.
If I connect pin 3 to the coil of a relay (with protective diode) it will pick and drop it fine, so as a last resort I can use a relay. I would really like to use a transistor though.
I've tried a BFY51 and a high power NPN transistor (who's part no I have forgotten at the mo!) which I robbed out of a PC PSU. The datasheet for this states Ic to be 6A or more, so that should suffice.
The maximum load will be around 15W in thoery. Practice should be much lower. I'd like it to be able to handle similar to the original 47W (21W+21W+5W).
Anything I'm missing?
Cheers.