[Amps] step start /triacs/Line Side Regulator

[TexasRF at aol.com]

Hi David, I am working on a power supply project with a similar  
application. My project will be used with a twt and I would also like to keep  the 
voltage from soaring during standby.
 
I found that a resistor of the proper value wired in one leg of the supply  
voltage will do just that. In my case, 160 ohms did the trick. There is a 
relay  that shorts the resistor out during transmit to restore full voltage. 
There is  some heat loss around 15 watts so the resistor size is important.
 
A side benefit is the same resistor makes an excellent turn on surge  
limiter. It takes about 30 seconds to fully charge the capacitor filter but in  
my case there is a 3 minute filament delay so no problem
 
I have not tried the QST article approach but I know the author well and he 
 would not publish rubbish.
 
73,
Gerald K5GW
 
 
 
In a message dated 2/12/2010 6:11:01 A.M. Central Standard Time,  
dhallam at rapidsys.com writes:

In the  October 1987 QST there was a construction article for line side  
proportional control regulator for a high voltage power supply.  Its  
purpose is to prevent the HV from soaring under idling conditions when  
the tube was not drawing current.  The circuit uses a comparator to  
sample the HV and turn a triac in the primary of the transformer either  
off or on depending up the relationship of the sample to a reference  
voltage.

I don't think I have ever seen this circuit implemented in  any designs 
or any discussion about it.  I am building a new amp and  was thinking 
about using it.  Is it a good idea or are the draw backs  to it?

David
KW4DH

Jim Thomson wrote:

> Yep. Emtron  have been doing it for many years and it is superb.
> 
>  Alek,
> VK6APK
> 
> 
> ### ramping up over how long a  period of time,  5 x secs,  10 x secs
> 1x sec,  or what  I suspect is  from a zero cross point, up to the top
> of the  cycle.. [IE:  4.17 msecs]   ???? 
> 
> ##   will the triac  handle the huge pulses every 8.3 msecs?? 
>  
> ##  My problem with the SSR's is... they need a BIG  heatsink
> They should also be supplemented  with a breaker or  fuses.
> There is too much leakage current through them imo.  If  you
> are  working on an amp that has them,un-plug  from  the
> 240v line  1st.  
> 
> ##  IF you  decide on using SSR's... get one that has a 
> zero cross voltage turn  on.... and a zero cross CURRENT
> turn OFF. 
> 
> Later...  Jim VE7RF  
> 
> 
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