[AMPS] Bridge vs. Doubler

[Rich Measures]

>
>Regarding the question of the preferred HV P/s design, a full wave bridge
>vs. a doubler, I think the nod goes to the brdige for several reasons.
>
>First, I think the G3RZP comment about higher peak currents refutes AG6K's
>comment about wire size. If the currents were equal, Rich would be correct
>- however the transformer currents are not equal for a given output load
>current.  

€    What I am essentially saying is that for equal DC output voltages 
and currents using similar cores, a FWB winding has More than four times 
as much resistance as a FWD winding. 

> Conservation of energy applies, so if the rectifier circuitry
>raises the output voltage, the input current must increase.  The analogy is
>somewhat equivalent to an impedance matching transformer.
>
>Second, the voltage doubler circuits typical to ham amplifiers are in
>reality two half-wave circuits with the outputs stacked.  The percent
>voltage regulation for a full wave bridge is significantly superior to a
>half-wave circuit.  

€  depends on the losses in the transformer, the electric-mains' 
resistance, and on how much C is used in the filter.  

> Two half-wave rectifiers are not going to be superior
>to a full wave bridge if regulation is the criteria.
>
€  During positive and negative cycles in a FWD, filter capacitor 
charging is taking place.    

>IMHO, either circuit will work fine with the appropriate transformer. 
>There may be other factors too - for example, if your filter cap is a
>single oil-filled unit, I don't see how you can use a doubler without
>buying another, identical cap.  On the other hand, the rectifiers in a
>doubler only carry half the current so this might allow some flexibility in
>component sizing.

€  did you mean to say 'in a bridge', Dave?
>
>Hmmm...with regards to my posting a week ago about 2A diodes to run two
>amps off one supply, has anyone tried running two rectifiers off one
>transformer to power two amps?  My engineering intuition tells me that
>there might be a problem with a FWB, because if you look real close certain
>diodes will wind up in parallel.  However, if the two rectifiers were half
>wave this would not occur.  The idea of using half-wave vs. full wave might
>sound like heresy, but if it works OK in doublers why would it not be
>suitable in a single rectifier?  

€  because a doubler is full-wave -- i.e., current flows on both half 
cycles.  The trouble with half-wave is that DC flows in the transformer's 
secondary winding.   

-  later, Dave


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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