I assembled a two transistor LED driver buck converter for dropping the 12V input down to the 3.2 volts needed for the LED. My problem seems to be that the circuit wants to act like a simple 22.2 mA current limiter, as if I took out the inductor and capacitor (the D1 is reverse biased and does nothing). Then when I try to get it oscillating, the LED current goes higher than 22 mA, My expected behavior was that the circuit would take in a higher voltage at low current and convert it to a lower voltage at higher current. I was hoping for 9V at 9 to 11 mA would give the LED a full 20mA. Instead, the circuit is taking more than double that current and I´m guessing that a good part of that is wasted as heat and the LED is being overdriven – too much current.
Feb 5 – I have changed most of the parts to values from one extreme to another. I have not found an optimum point where the circuit did a better job of bucking the voltage. All of the values gave an oscillating circuit that really behaved the same as a simple 2 transistor current limiter. This current limiter can be visualized by removing the capacitor and replacing the choke with a short wire.
ehmm… where is the schema? 🙂
Yeah, I would like to know that, too. I uploaded a picture, and it finished the upload, but all I see on the screen is the broken picture icon like there is nothing there.
Finally found out why it wouldn´t allow the pics to upload.