[WIP] 17mm DD+single-7135 driver / single sided / Dual-PWM

[comfychair]

@fixed it

@comfychair

Or, forget all that nonsense and use a single 7135 controlled by a second PWM output for the low modes. Has anybody tried that yet? (/snark)

I think I read something about that a few months ago in some obscure GB thread But for what it’s worth, I’ve done some experimenting recently and found it’s possible to get beautiful, PWM-free low modes from the FET by giving the gate a small charge from the pull-up resistor (about 150-250 cycles @ 4.8MHz on the attiny13a). It can then be left floating for a while. The nice thing is that it makes a nice linear looking ramp, probably because the FET has exponential response to gate voltage. It will also go as low as you want it too, with the led barely visible in a dark room. The ugly part is that the charge time needed changes significantly with voltage and probably also from part to part and with temperature. So this will be difficult to use without some sort of feedback loop but I’ve not given up on it yet.

Read this piece of ancient history. Feel free to laugh.

It does work, I've built the circuit with a 10K pot (higher would be better, since it's wired direct between B+ and B-) as texaspyro describes there. The FET does get uncomfortably hot in the upper half of the range, like between 70-98%. At WOT it stays cool.