Guru
Joined: 09/08/2007
Location: AustraliaPosts: 4406
| Posted: 10:53am 04 Nov 2017 |
I just placed a short across R27, the C30 capacitor I suspect, is just there to block any high frequency noise. Its not critical, and could be removed.
With R27 bridged, the Ifb now instantly turns off the IR driver chip, and when Ifb falls below the threshold the PWM soft starts via software, its not C30 providing the soft start action.
It soft starts very gently just as it normally does at initial power up.
With R27 removed, Ifb only works on the enable pin of the IR driver chip, and its a very sudden and violent all or nothing on/off action. I have no idea why R27 was removed.
The way I have done it, is to use the SCR latching circuit others here are using that turns off the PWM pretty fast. Then wire a normally open push button directly across the SCR as an over current reset button. When reset is pushed, the system soft starts, but only if R27 is bridged.
Pushing this reset button at any time instantly shuts down the PWM, and it soft starts back up again.
Many ways to skin the Ifb cat...
Cheers, Tony.