[ARC5] Receiver AC Power Supplies

[Bill Cromwell]

Hi Jim,

It seems to me that you are right about the full wave bridge having 
twice as many diodes. However, in each of those bridges only half of the 
diodes are conducting at any one time. The forward voltage drop of the 
nonconducting diodes shouldn't figure into it since there is no forward 
current, ignoring miniscule leakage currents. That does leave twice as 
much voltage drop across the full wave bridge as in the full wave center 
tapped circuit but the full wave bridge has about twice the AC voltage 
applied, too. Depending on output filter parts, loads, and arrangements 
the voltage is going to vary some from 'expectations' anyway.

Either way will work just fine for the recevers. In my power supply I 
have the 25 volt center tapped RS transformer connected to the power 
line and the output applied to the heaters. One half of that is to be 
applied to another, much smaller RS 12 volt power transformer to work in 
reverse and furnish B+ somewhere north of 100 volts DC. It is only 
intended to operate *one* receiver at any time. I'm considering 
rectifying and regulating the heater supply as well. And I will be 
adding noise/rfi filtering on the AC side. So far my weekend schedule 
hasn't eroded my hobby time too badly so I might actually 'get 'er done' 
and have those radios back on the air where they belong. Before, I had a 
small, separate B+ transformer and the primaries in parallel across the 
power line. That antique iron finally just quit.

73



On 12/12/2014 10:52 AM, Jim Wiley wrote:
>
> Wayne -
>
> Yes, that is correct.  The transformer can provide a total of 50 watts 
> (approximately).
>
> So a full-wave center-tap rectifier could produce roughly 12-volts at 
> about 4 amps, where a full-wave bridge will make roughly 24 volts at 
> about 2 amps.
>
> The nominal 12-volt output voltage using the half-wave will be a bit 
> higher, percentage wise,  than the nominal 24-volt voltage, since the 
> bridge rectifier has 2 more diodes, with their attendant voltage 
> drops,  to deal with than does the full-wave center tap 
> configuration.  Depending on diode type ( Germanium, Schottky 
> barrier,  or conventional silicon construction), each diode will drop 
> between 0.3 and 0.7 volts.   Conventional silicon diodes are most 
> common.  Schottky barrier are next, with Germanium becoming obsolete 
> and hard to find.
>
> - Jim, KL7CC
>