[Sussex] Outcome Re: OT: another hardware question

[Antony]

Desmond Armstrong wrote:
> > The circuits you found got me wondering: could a simple triac controller
> > like [3] be run in DC mode as in [4] circuit 1c, and fitted with an RC
> > on the gate so as to ramp up when power is applied?  It's beyond my
> > skills though - any offers?
> 
> No.
> 
<snip>
> 
> The triac is an on-off avalanche device <...snip...>
> Philips did take up this proposal and make triacs 
> with only the 3 quadrants of usability. The benefit is vastly improved 
> dv/dt capabilities.
> 
> It would be interesting to do more motor speed control work using this 
> new generation of triacs. But that would require much time.

Do you mean this high dv/dt device would be essential for use on
rectified AC, but be hard to design for properly?

I hoped that DC mode would make it easier to provide a ramping (fixed at
2 seconds) gate voltage, leading to a simple DIY circuit adequate for
amateur use.  If the current never drops sufficiently for a triac or SCR
to turn off, how about controlling AC using two SCRs back to back with
RC circuits on their gates?

Anthony