/diy/ - Do It Yourself

>>1462120
I have a shitty circuit I made by accident. I was trying to do a PWM with a 555, but I accidentally mixed up the schematic with the VCO. I created this broken ass circuit which changes frequency, and requires tying a relatively low resistor between control voltage and ground, but between 0 and Vcc, you can get a PWM signal for a logic-level mosfet, which works between 400Hz near max percent and towards 1000+ Hz at low percent. It's near linear for brightness and I don't know why it works, but it does.
The CV problem is that the CV is internally biased, but with a high input impedance. If your CV source has a good source but bad sink, off is biased on 50% or 2/3rds Vcc. The lower the input impedance on your source the better the circuit works. At about 1k bleed for off, you get 10% min brightness 1000 kHz. At 5V 100hm input with bleed resistor, you get >90% on. This circuit was tuned more for a pot (1-2k pot) but if you used an op-amp real-zero buffer, you wouldn't need the bleed resistor as long as you can supply/sink around 20mA. I tested with a 250 ohm impedance and no bleed resistor on CV, and you get near 0 and near 100%.

I don't remember if I considered the input buffer or not, since many digital boards only source a few mA on their analog pins. I also focused on 5V Vcc, 0-5V input, and logic-level mosfet output.