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@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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>
>
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