Topologies like push-pull, half-bridge and full bridge don't
require dead time to reset the transformer core. Though
that doesn't mean the switch's conduction times can overlap
which causes shoot-though current.

I think what kills the push-pull in this case is overlapping
conduction times not core saturation.


For amplifier power supplies it would simplify things to
do the regulation at a lower voltage and keep the HV parts
at a minimum. Phase controlled 60Hz switching is ok but
this might be a better way.

There's a use for push-pull or half-bridge or full-bridge
where the switches duty cycles are not modulated and the
frequency is fixed. The switches run as close to 50% duty
cycle as possible without overlap. It's called a "DC
Transformer." It's one of the building blocks of compound
converter topologies. Handy because it offers isolation
and a fixed ratio of step-up or step-down with a DC input
and output.

Since there's minimal dead-time and no output inductor is
required. The efficiency can be very high. The control
circuit is an oscillator running at 2F (Like a 555,) followed
by a flip-flop and a couple of gates to insure there is never
overlap. When using MOSFETs an RCD network on their gates
will work, though I favor using logic gates.

So if you built one of these with a 10:1 ratio you could
put 200VDC in and get 2000VDC out. Any regulation or
protection would be done to the 200VDC input. This might
not be a bad idea... your 2KV output stage now consists
of only rectifiers and a capacitor.

Doesn't have to be 200V, pick the voltage that makes it easy.

Just a thought.



raypsi wrote in news:f60045d7-f5a2-4dbe-a850-
:

Well I remember repairing Sony TV push pull SMPS I made a living from
replacing many a blown PP pair. Sony then went to PP pair in a single
package. That reduced the business for me but I had much experience
repairing them already. Trick with the Sony push pull was 2% timing
components. The PP had to be within 2% of 50% duty cycle. They used a
self starting multi vibrator design. After replacing the blown parts
I'd power the input up at 20vac and use a 12vdc supply for the start
up circuit, Then check the waveform on a scope to make sure it was
with 2% fo 50% duty cycle. There was no dead time in the Sony's. They
just varied the frequency to regulate the voltage.

73

n8zu