Symmetrical supply rails with a 2 wire transformer, is it possible?

[Bricolo]

I've got a transformer with only 2 wires on it's secondary (and only one secondary)

is there any method to obtain -,0,+ ?

 

[grataku]

A DC-DC converter? I would guess that's only for low power stuff...

 

[mermoz]

try this:

 

[Sch3mat1c]

I suppose that'll work...but you can do better with a true full-wave voltage doubler. You can even use a bridge rect. here, though half the diodes act in parallel (IIRC), so it's less effective. (This strategy is used in dual-voltage switching supplies, where a switch or jumper changes it from FWB to FWD mode. Yep, the primary circuits have 340VDC on them!)
Anywho - it's basically two half-wave rectifiers pointing in opposite directions. One end of the transformer feeds a 'CT' between the two main filter caps, the other end feeds diodes which pump the caps alternately. This is known as a full-wave doubler because the ripple output is 120Hz, due to the stacked nature of the circuit.

I'll grab a circuit in a second...

Tim

 

[Rudy]

This is also a pssebillity, little bit easy'r

some minor points
- buffer elco's must be 2X bigger then normally
- diodes must be able to handle a lot of current

note, total output voltage is double then normally

Greetz Rudy ( dahm dots )

 

[Sch3mat1c]

Yep, that's the full-wave I was referring to.

Here are some circuits to mull over. The CT between caps (on the FWD) can be used as a half-voltage (wrt. negative) or ground point.

Tim

 

[e96mlo]

mermoz, if the earth symbols are supporsed to be the same node in your schematic, then there is no longer galvanic isolation.

/Marcus

 

[Bricolo]

wich one to choose?

 

[grataku]

Bricolo,
no one has asked what do you intend to do with this...
Clearly voltage doublers are not the optimal solution if you care about ripple, otherwise why bother with the two secondaries, right?

 

[jackinnj]

voltage doublers and ripple

if you increase the capacitance the ripple can be dealt with-- or at least you can calculate the % ripple at a given load -- the problem is that capacitors quickly become more expensive than transformers.

 

[Bricolo]

Bricolo,
no one has asked what do you intend to do with this...
Clearly voltage doublers are not the optimal solution if you care about ripple, otherwise why bother with the two secondaries, right?

It's too hard to wait for the transformer I ordered
I want to test my gainclone with the spare parts I've got

 

[Circlotron]

try this:

Definitely won't work. Transformer is s/c by upper bridge top left diode in series with lower bridge bottom right diode. Sorry to be a party pooper.

 

[mermoz]

Bricolo, Circlotron

Definitely won't work. Transformer is s/c by upper bridge top left diode in series with lower bridge bottom right diode. Sorry to be a party pooper.

I apologise for this hasting post ! sorry Bricolo !
I will learn to use sim tools a bit (a lot of bits !) better and will improve my electrical understanding skill, before replying to other similar posts

 

[analog_sa]

Quad derive +-0 from a single secondary in most of their power amps (beats me why). Have a look at the 306 per example. I think they use a simple circuit to equalise the current through the supply caps.

cheers

peter

 

[moamps]

It's too hard to wait for the transformer I ordered
I want to test my gainclone with the spare parts I've got

Hi,

Rudys schematic is OK. This is half wave rectifier. I use them. Caps must be bigger, 4700uF or 10000uF for little ripple. Note; ground (0V) is connected to connection between caps (upper - and lower +)

Regards
zzeenn