[AMPS] Bridge vs. Doubler

[Peter Chadwick]

Rich said:

>The trouble with half-wave is that DC flows in the transformer's 
>secondary winding."

And in the primary. Which is why the IEC specs limit the amount of DC
component that can be drawn from the AC supply. Admittedly, they're shutting
the stable door after the horse has bolted..............

In the mid 50's, 60's and 70's, most TV sets over here used a live chassis,
no power transformer, and a half wave rectifier. Until the 50's, many houses
had reversible (non polarised) 2 pin mains sockets, but in the 50's 3 pin
sockets (live, neutral, earth) became the standard. Thus, although there was
a good chance originally of TV sets being plugged into the mains either way
round, this disappeared - the DC component was all the same way round. The
resultant major DC load on the supply mains at popular TV viewing times led
to a spate of electricity substation transformer fires, because the DC
saturated the transformer core. At best, it blew the fuses before the
transformer went up.............

Which is why there are limits on how much DC you can put down the mains
these days.

I believe that in the US, power transformers were used in the majority of
TVs, with full wave bi phase rectification, but whether or not this was the
reason, I don't know.

But half wave sure puts DC on the secondary - which is why the transformer
utilisation factor is so low.

As far as the doubler v. full wave bridge argument is concerned, I don't
think it's clear cut, but  is case dependent.

73

Peter G3RZP



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