Power supply transformer ratings

[deskmate88]

I have two 530VA 2X40V toroid lying around, can I use this for the gainclone project.

1. IMHO the output voltage is too high, is there any way to reduce the output voltage (like using a half wave rectifier)?

2. Also is the VA rating too much?

3. why no one use EI transformers for this application?

many thanks

DM

[elizard]

voltage is way too high

there's no such thing as too high VA rating

some people do use EI for their gc

[deskmate88]

Thanks.

Could someone also kindly help me to understand the DC output voltage of the attached configuration (220V version)?


As I understand, it is a full wave rectifier with a capacitive load (also take into account the 1000uF caps, shall I?), some the DC voltage should be:

Vdc = 0.71 x Vac

and the Vac is 96V (48V x 2) in this case ... how can it be? way too high?

Where did I made a mistake?

[deskmate88]

Anyone?


BTW, if this configuation is used, what VA rating of the transformer shall I use? is 100VA good enough, or 160VA better?

does this also mean I need 4 x 100VA (or 160VA) per channel?

Many thanks.

[theChris]

out of curiosity, what are the caps and diodes between primaries for? some kind of low-level DC removal? and 1uF is pretty small for a filter cap.

and why not just draw it as 4 diodes in a row down in parallel with 4 in a row up?


also, the unloaded Vdc will be about 1/0.707 or 1.414 Vac, this is because the caps will chrage to the peak voltage, and without any load they will never discharge. adding a load will create a ripple voltage which is pretty high with 1000uF. an approximation is
I = C dv/dt = C Vrip 2 pi f
so
Vrip = I/ (2 pi C f)

where f is either 50 or 60 for half-wave, or 100 or 120 for full-wave.

i assume your looking for voltage rails of about 24-33V per rail, +-24 to +-33V ?