audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Ante,
My PWM oscillator is at 3.9KHz so when it is fully dimmed, the off pulse width is 256us and the on pulse width is probably only 245ns! A totem pole (push-pull?) output would probably speed the turning off somewhat and help dim the LED, but maybe it wouldn't be enough.
The dimming occurs on my 'scope trace too and before it completed dims away the pulse looks like an extremly narrow triangle wave, it slowly slews down then doesn't even reach very low before it slowly slews back up (when I say slowly I am talking about tens of ns). The cap I added from base to emitter of the LED driver transistor reduces the narrow pulse pretty well.
My PWM oscillator is at 3.9KHz so when it is fully dimmed, the off pulse width is 256us and the on pulse width is probably only 245ns! A totem pole (push-pull?) output would probably speed the turning off somewhat and help dim the LED, but maybe it wouldn't be enough.
The dimming occurs on my 'scope trace too and before it completed dims away the pulse looks like an extremly narrow triangle wave, it slowly slews down then doesn't even reach very low before it slowly slews back up (when I say slowly I am talking about tens of ns). The cap I added from base to emitter of the LED driver transistor reduces the narrow pulse pretty well.
