I am making a car tach calibrating device so you can accurately re-install the needles to there correct location. But the Tach uses probably close to 1 amp to run. The typical 555 doesnt support this amount of current output. I tried a TIP31 and it did not work. I have a few NPNs and Mosfets laying around, but before I just start to throw them in to test, I thought I would ask if anyone has a simpler solution. This circuit is a square wave design, The amplitude is the cars voltage, approx 13v. The frequency change is what is realtive to the rpms. I have written in the below schematic the referances to this. I also added a simple NPN with a 1K to base resistor. But testing gives no output. I have read that some Darlington arrays may work. I have also read the appropriate term for this NPN is called "COMPLEMENTARY SILICON POWER TRANSISTORS". But before I go out and buy something on a hunch, maybe I can get the right answer here.
Stu
Stu