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Voltage Dbl'r/Triplers and Specs


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12/29/2004 6:56 PM
Glenn
Voltage Dbl'r/Triplers and Specs
Hey guys!  
 
Is there a cookbook method to determine the parameters involved in selecting a tranny that you KNOW you're going to have to use a Voltage Doubler/Tripler scheme to get it in the proper range?  
 
Basically, I'm interested in doing a preamp build using a Hammond Toroid PT, but the highest B+ I can get w/ traditional PS schemes would be around 330Vdc (unloaded). I need some more B+ than that (so I think, anyway).  
 
When you double the voltage output, you half the current capacity (when you triple the V, do you take 1/3 of current capacity or is it more/less). Which secondary/tap voltages should one use in their calculations for this approach. I'm fairly certain I can get the current rating correct from what I 'know' thus far...LOL I'm sure many other folks may benefit from this one! LOL TIA!  
Glenn
 
12/29/2004 7:29 PM
Don Symes

If the toroid's secondary has a CT, and your calculations so far assume a grounded CT, have you considered letting the CT float and grounding one of the 'outside' legs? That should get you to a 2X AC voltage at the full current.  
 
An ideal transformer - and an ideal PSU - are constant-power devices, so tricks like voltage doubling/tripling have to take that into account.  
 
... Now that I seem to have contradicted myself, let's hope one of the smart guys jumps in.
 
12/30/2004 10:49 AM
Wild Bill

Get ahold of any old copy of the ARRL Radio Amateur's Handbook.  
 
They will have a whole chapter on power supplies, including voltage multiplier circuits and formulae.  
 
This is such a great reference book that every amphead should have one! The best of course are from the days of tubes - ham flea markets usually turn up a copy or two.  
 
You'll find lots of construction info like resistor/cap colour codes, wiring colours for transformers both power and audio, tube pinouts and data specs, and as much theory as you care to swallow!  
 
To answer your basic question, take the voltage and current rating of the winding and multiply it to find the VA (Volt-Amp) rating of the winding. As you already thought this is your constant. If you up the voltage you have to derate the current to get the same VA. So a voltage tripler can deliver only a third of the current, or actually slightly less due to circuit component losses.  
 
---Wild Bill
 
1/1/2005 12:29 PM
Andy

I have a copy from 1950 here on my shelf... I find it to be a very valuable reference at times.
 

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