[Sussex] Outcome Re: OT: another hardware question

[Desmond Armstrong]

Antony wrote:
> Desmond Armstrong wrote:
>   
>> Antony wrote:
>>     
>>> 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?
>>>       
>> No, you can't do that either, as the thyristor is simply 1/4 of a triac 
>> (or 1/3 of a modern triac).
>>     
>
> Not 1/2?  I guess this wouldn't do the trick then?
> AC live - diode - R - (to diac) - R - {R || C} - AC neutral
>
>   
In brief the triac consists of 4 parts (quadrants) namely:-

1/ gate positive anode positive
2/ gate positive anode negative
3/ gate negative anode positive
4/ gate negative anode negative

The really troublesome quadrant is number 2.
The presence of this very troublesome quadrant causes reduced dv/dt.
This quadrant is the least sensitive for triggering.
So removable of this quadrant means that the dv/dt can be very much 
improved without any disadvantages.

If one uses the diac then you are using quadrants 1 and 4
If you are using an electronic circuit then you would use quadrants 3 and 4

I was involved in the recommendations to remove quadrant 2 from the 
triac, and at the time other electronic engineers always used quadrants 
1 and 2. They did take some convincing that we must rethink our designs. 
The problem was that with a knowledge of physics I was able to optimize 
the interfacing of the triac and the drive circuitry.

Remember also that a thyristor is simply one quadrant of the triac, and 
is quadrant 1 only.

>> I can see that I will have to talk to you on the elements of phase 
>> control of these devices. And a bit about controlling AC as well.
>>     
>
> Thanks I'm looking forward to that, be gentle!  ;-)
>   

My role these days is sharing what knowledge I have and I do not expect 
that everybody knows everything.
The main reason for doing what I am doing is the constant challenge and 
constant learning of new things.

Now that I have the 'opensolaris bible' which I won in the raffle for 
the 4th anniversary of opensolaris I do have a lot of homework to do 
before the next opensolaris meeting.