Squeezing 24v out of a 12v tranny, plus a ground Q.

[Sammas]

I've got a 12v 25va toroidal that i was hoping to use temporarily while a bigger 50va 24v tranny is on its way (still two weeks til it arrives).

If i wire the two secondary windings in series i'll get 24v (wiring 12v on one secondary to 0 on the other secondary), correct? Wiring the two secondary windings in parallel will double the current... I'm pretty certian i've got it the right way around, yeah? :? It doubles the number of windings used together.

So the tranny no longer has a centre-tap? Do i just run 0 reference from the PSU board straight to ground to meet with the Star ground i have (where chassis, audio and IEC meet)?

This is part of an external PSU which is connected to the preamp enclosure via 5-core + 5pin socket. I've wired the 5-core with V+, V-, 48+ and ground... Inside the preamp enclosure, I've connected the audio, chassis and power grounds together at the Ground pin of the 5-pin socket. Inside the PSU enclosure i've taken the ground pin to meet at the star ground with the chassis, and psu (?) ground as well as ground pin of the IEC socket...

Is this a viable method? I do have a spare pin on the 5pin socket, should i maybe keep the preamp power ground seperate until the star ground in the PSU enclosure?

Wow... i hope that made some sense.

This is for a 312 type preamp that is running off 16v and draws about 100mA.

 

[Samuel Groner]

I don't understand exactly what type of PSU you want - +/- 16 V?

If this is your goal, you need two secondaries, or you will not end up with a dual supply. I guess for a temporary solution, the 12 V could be OK for a +/- 16 V supply if your mains are not low and you use big enough filter caps.

Samuel

 

[Svart]

it is unclear if you want a differential supply or a single supply.

if you want 24v, then wire the two secondaries in series but don't reference the centertap to ground. you will double the current in this config. rectify and reference the - of the bridge to ground.

if you want a differential supply, the 12v secondaries rectified should give you around +-16v. you could easily feed this to 15v vregs as the 25va trafo shouldn't sag with only 100ma on it. Do reference the center tap to ground in this situation.


:thumb:

 

[SSLtech]

[quote author="Svart"]12v secondaries rectified should give you around +-16v. you could easily feed this to 15v vregs...[/quote]

You can feed it to them, but they won't regulate happily at a margin of a volt or less.

12V peaks out at about 16.9V, minus the (approx) 1.2V "rectifier tax" would leave you with a little over 15.5V, plus whatever the trasformer feels like giving you fer being a gentle user...

I reckon a typical 7815/7915 might complain very bitterly about that...

Keith

 

[Svart]

yeah that is on the very margin of working. most regulators need to see 3v over their output to work to their potential but as long as you can keep the current levels steady, it could work long enough for him to get his new trafo.


or use some super duper schottky diodes and only get .3v taxation..

i wonder if the IRS just needs new diodes.. ??