Is it possible to get these regulated voltages from a 18V AC transformer operating without any problems ? Need it for a preamp and i have an external transformer i would like to use if possible (center tapped, 2 * 18V AC, 1.4A).
Don't know how much current i need yet but at least a lot less than 50% of that.
Don't know how much current i need yet but at least a lot less than 50% of that.
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Yes this is possible. The VRDN dual regulated power supply board here on the Forums, shows one way how. This type of circuit can accept either a single secondary transformer (like an AC wall wart) with two secondary wires, or a dual secondary transformer with four secondary wires. But not a "center tapped" transformer with three secondary wires. VRDN's voltage outputs are adjustable from ±11V to ±20V , max current is 1 ampere per side. LINK .
full wave voltage doubler gets you +-25vdc unloaded, so depending on your transformer, it is possible to get +-22vdc..
I know that there is enough voltage before the regulators, more thinking about possible stability/performance/load problems when using regulated DC voltages higher than the transformer AC out voltages.
without telling us your loads and your transformer specs, it will be hard to tell, a transformer weighing in at 1kg will underperform one with 5kg weight...more likely with same terminal voltages and unloaded...
I wrote that in the first post, i might have missed something
Transformer out: center tapped, 2 * 18V AC, 2 * 1.4A
Requested DC out: +- 20v DC or +- 22V DC.
Load less than: 600 mA per DC output. + and -.
Transformer out: center tapped, 2 * 18V AC, 2 * 1.4A
Requested DC out: +- 20v DC or +- 22V DC.
Load less than: 600 mA per DC output. + and -.
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It is possible, yes. Is there a pre-made printed circuit board that you can buy, which implements one of the possible solutions? I personally don't know of one, but it is certainly possible that one or more might exist. OR you can just engineer your own and then offer it for sale {or free !!} to others.
The problem is that center tapped transformer circuits are, more often than not, "wasteful". The cost savings versus dual secondary transformer circuits are negligibly small, but CT circuits generally create twice the output ripple (noise). So for the same money you get half the performance. Ick.
The problem is that center tapped transformer circuits are, more often than not, "wasteful". The cost savings versus dual secondary transformer circuits are negligibly small, but CT circuits generally create twice the output ripple (noise). So for the same money you get half the performance. Ick.
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ok, 18-0-18 in FWB gives you 50vdc unloaded, split that and you get + - 25vdc your regulator must be low dropout type as you only have 3 volts to work with...switching dc to dc regulator will work best for you unless you are willing to go + -15 volts dc..
Thanks for the info so far everyone. I will do my own PCB for this that will make things a little easier than trying to find one to buy.
So if i chose +-20V DC i can base it on LM317/LM317 and it will be ok ?
And if i chose +-22V i need better regulators with lower droput to avoid possible "problems" ? Any suggestions what to use ?
So if i chose +-20V DC i can base it on LM317/LM317 and it will be ok ?
And if i chose +-22V i need better regulators with lower droput to avoid possible "problems" ? Any suggestions what to use ?
How about a 9V transformer to boost the incoming AC voltage, so you can use LM317/337?
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@chrisng
I never used this approach in a PSU before, so i don't know if there is any "problems" with it. I have the space for it is so if this works ok it might be an option. Do you know any example of it and what type of transformer to use. I can use higher than +-22V DC out so higher voltage is not a problem.
I never used this approach in a PSU before, so i don't know if there is any "problems" with it. I have the space for it is so if this works ok it might be an option. Do you know any example of it and what type of transformer to use. I can use higher than +-22V DC out so higher voltage is not a problem.
Since the load draw less than 50% of your transformer rated current, increase 9VAC to the primary winding shouldn't be a problem. However, it only boost the secondary voltage from 18V to 19.35V.
Bucking (And Boosting) Transformers
Bucking (And Boosting) Transformers
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