Thyristor bridge for current control?

Question

HelloI am in the process of trying to cobble up a method for creating a DC supply with a variable output current. The plan (on a basic level) is to use a current-limited (variable shunt) AC transformer (from an AC welder), then a thyristor bridge, followed by a smoothing choke.If I control the thyristor gates in such a manner as to delay the forward conduction of current (by a number of degrees delay per half cycle), will this have the effect of providing me with a variable current supply on the other end of the smoothing choke?This is my first time playing with thyristors, and I would greatly appreciate any insight/correction as to my line of thought so far with this.Thanks,Jon

Jan Panteltje · Accepted Answer

On a sunny day (Wed, 30 Apr 2008 14:43:49 -0700) it happened "Jon Danniken" wrote in :

Yes current limit will work. It is slow though, due to energy stored in the magnetics, and also you cannot switch of anytime, just at the zero crossing. So if you short something like that, you still get a current overshoot.

Jon Danniken · Answer

Hi Jan,Thanks for the encouragement; I'm glad to know I'm on the right track.  A concern I had was if I needed to "chop" the incoming AC wave more frequently than once per half-cycle, but it would certainly be more simple to just do it once per half-cycle.The application for this will be a form of welding (tungsten/gas), so there very well may be the occasional short circuit.  Mainly I am needing a way to vary the current at the beginning and at the end of a work cycle.Thanks again,Jon

cbarn24050 · Answer

lyas.You need to make sure you allways keep the transformer balanced.

Jon Danniken · Answer

Hello, cbarn, thanks for the reply.  I am a bit confused as to what you mean by "transformer balance'; would you be able to specify the phenomenon you are referring to?Jon

cbarn24050 · Answer

ent you meanI mean use both half cyles the same.

Thyristor bridge for current control?

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