Hi,
Lets do it a different way...
In an old magazine i found this schematic...
I changed it a little and made a test circuit with a LT1083.
Q3 measures the diverence between the input and the output of a regulator, here a LT1083.
When the difference is large enough, then Q3 will give a pulse to the gate of the thyristor.
Now T1 stops the charging of the buffer capacitor C1.
It differs from a "normal" thyristor circuit is, that the charging is stopped, when sufficient energie is present in C1.
Charging will start again at each zero crossing and is switched off again when sufficient energie is in C1.
A typical thyristor circuit turns "random" on, this would create interference pulses, there are large coils necessary to suppress current spikes.
R4 and C3 controles the switching off, adjusti these values for minimum noise from the transformer.
If you make C3 to large, the noise( al little, much better than a normal Thyristor controler) is gone, but the dissipation in the IRF5210 wil be Higher.
Dutch site were i explane how its works, use google translate
http://www.circuitsonline.net/forum/view/110029/11And then this, do NOT use a normal bridge circuit if you want a high efficiency powersupply, use a
LT4320 electronic Bridge controler.
http://www.bramcam.nl/NA/NA-01-PSU/LT4320On the same website/topic you can see some testing i have done with a LT4320, its a beautiful IC!
It is very difficult to build a low-noise power supply with a switching pre-regulator (30Hkz - 2Mhz)
The switcher is like a lighthouse in a darkroom
Just 2 cent's
Kind regarts,
Blackdog