HELP! Toroidal Power Transformer

OK, I bought two wrong toroidal power transformers.

I need 18V-0-18V output, but obviously my brain wasn't working when I picked mine from the manufacturer product list.
I should have bought "Output Series 36V", instead of "Output Series 18V".

I can't return it, and probably can't sell it because no one wants to buy it.

So, l wanna use it. Can someone tell me how to hook it up with any of the 15V/18V dual regulated power supply projects here, please? I reckon the downside of it is that I will get a half wave instead of a full wave, correct?

Thanks a lot folks!

You sure you can't use it. Does it have two 9vac secondaries?

check this : -
http://www.manaservice.com/img/ma/fig/transformer_connections.gif

You can probably make a virtual CT with a couple of 100ohm resistors.

A 9-0-9 center tapped secondary can be used as a  18-9-0 winding by grounding one end instead of the center-tap. Now you will only get half wave rectification so more ripple voltage and may require larger reservoir capacitance.

JR

Yea, I have 9V-0-9V AC instead of 18V-0-18V AC. 18V AC is ONLY without a center tap.

The power transformer is VPT18-1390 made by Triad Magnetics.

My power supply circuit uses LM317 and LM337, and the only possible solution I have currently:

I set my LM317 and LM337 to accept 9V AC, and generates output of +8V and -8V DC respectively.
then into DC voltage doubler circuit, which will get me the needed +16V DC and -16V DC supply.

Problem is, I haven't found a DC voltage doubler circuit that can handle 700 mA current (full load)

You have 18VAC only not both polarities at the same time.

Look up what half wave rectification means.

You charge the +18V supply on the positive swing and the -18V on the negative swing.

JR

PS: A voltage doubler could work, but will be more complicated and parts intensive than half wave rectification

JR, while searching, I came across a pirate blog about a DC voltage doubler which uses TI LM2586 step up 3A flyback regulator.

Looking at the datasheet, there's a reference schematic for a 12V DC voltage doubler from a 6V DC input, which should be able to 7.5V DC to 8V DC input with a little modification. The number of components are quite minimal.

metalb00b00 said:

JR, while searching, I came across a pirate blog about a DC voltage doubler which uses TI LM2586 step up 3A flyback regulator.

Looking at the datasheet, there's a reference schematic for a 12V DC voltage doubler from a 6V DC input, which should be able to 7.5V DC to 8V DC input with a little modification. The number of components are quite minimal.

Click to expand...

Compared to half wave rectification which uses less parts than even full wave rectification?

If you choose to not listen, I choose to stop offering advice.

See ya.


JR

Oh sorry. It's not that I don't listen to your advice. I'm a little intrigued with that DC voltage doubler circuit that's all, hehe.

metalb00b00 said:

Yea, I have 9V-0-9V AC instead of 18V-0-18V AC. 18V AC is ONLY without a center tap.

The power transformer is VPT18-1390 made by Triad Magnetics.

My power supply circuit uses LM317 and LM337, and the only possible solution I have currently:

I set my LM317 and LM337 to accept 9V AC, and generates output of +8V and -8V DC respectively.
then into DC voltage doubler circuit, which will get me the needed +16V DC and -16V DC supply.

Problem is, I haven't found a DC voltage doubler circuit that can handle 700 mA current (full load)

Click to expand...

As John already told you, just combine your transformer secondaries in series, one winding end to one of the psu-AC inputs, other winding end to psu-center-tap connection for 0V reference voltage, leave the other psu-AC input unconnected. Done.

I have learned some very valuable life lessons today.

Quit while you still can, leave when you're not welcomed anymore, and not to let your mind wander off when someone has suggested something important to you.

Sorry I screwed up. Thanks for putting up with my stupid questions. Wish you all the best.

Farewell.