Dual rail from trafo with no CT?????

madtecchy · 12th January 2011, 07:43 AM

Hello all
Will this psu have high ripple compared to the usual dual rail ct psu.
Im guessing there may be other problems too.
I have built it out of salvaged parts and the voltages you see are what i tested with my dvm no load applied.
Kind Regards
Mark

DF96 · 12th January 2011, 11:05 AM

Yes, it will have higher ripple as it is essentially two half-wave supplies connected in series. Alternatively it could be viewed as a voltage doubler. You will need more smoothing, but nothing fundamentally wrong with this supply.

Andy5112405 · 12th January 2011, 11:38 AM

How much current are you after ?

madtecchy · 12th January 2011, 11:58 AM

Hi andy it is just a product of my thought . i like to salvage parts from old discarded electronic equipment and this would be a way to use single winding transformers to power dual rail amplifiers. im guessing the current would be shared between the rails so maybe less than half the current per rail.
And DF96 do you think it would have approx double the ripple ????. i will dig out my old scope later and have a look at this circuit when it has a load attached.
Regards Mark

Andy5112405 · 12:27 PM

Personally I would build a Buck Regulator to generate a -ve supply from the +ve.

If space allowed I would also consider using the LT to drive an SMPS with the required split secondary.

If you only want low current - ie Op-Amp level, then you could employ two resistors in series across the supply and use the junction as 0V but this is only good at low current.

You could also employ two regulators, one on top of the other, the junction forming a psuedo 0V.

madtecchy · 12th January 2011, 12:18 PM

Hi Andy
Thankyou for the alternatives i should of said i like the idea and topology of keep it simple stupid.

Andy5112405 · 12th January 2011, 12:42 PM

Realistically though, WEO the SMPS approach you are not going to get any appreciable current out of a pseudo 0V approach.

hotiron · 12th January 2011, 01:17 PM

This is how Cirrus Logic does it on their evaluation boards.
If its good enough for them I reckon its good enough.
See page 17.

http://www.cirrus.com/en/pubs/rdData...cs4392eb-1.pdf

grenert · 12th January 2011, 02:31 PM

Quote:

Originally Posted by hotiron

This is how Cirrus Logic does it on their evaluation boards.
If its good enough for them I reckon its good enough.
See page 17.

http://www.cirrus.com/en/pubs/rdData...cs4392eb-1.pdf

That's not a rectifier circuit (those are zeners in the Cirrus Logic circuit).

madtecchy · 12th January 2011, 03:02 PM

Andy are you a fan of smpsu's.
I dont think this circuit will have too many problems
supplying current. however im sure it will need lots of smoothing.
I had a look at the cirrus link yes they are zener's and yes it is not a rectifier.
regards

12th January 2011, 12:09 PM	#5
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	Personally I would build a Buck Regulator to generate a -ve supply from the +ve. If space allowed I would also consider using the LT to drive an SMPS with the required split secondary. If you only want low current - ie Op-Amp level, then you could employ two resistors in series across the supply and use the junction as 0V but this is only good at low current. You could also employ two regulators, one on top of the other, the junction forming a psuedo 0V. Last edited by Andy5112405; 12th January 2011 at 12:27 PM.

12th January 2011, 01:17 PM	#8
hotiron diyAudio Member Join Date: Feb 2007 Location: Aberdeen Scotland	Cirrus Logic This is how Cirrus Logic does it on their evaluation boards. If its good enough for them I reckon its good enough. See page 17. http://www.cirrus.com/en/pubs/rdData...cs4392eb-1.pdf __________________ If you give up easily Dont start!!

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12th January 2011, 11:05 AM	#2
DF96 diyAudio Member Join Date: May 2007	Yes, it will have higher ripple as it is essentially two half-wave supplies connected in series. Alternatively it could be viewed as a voltage doubler. You will need more smoothing, but nothing fundamentally wrong with this supply.

12th January 2011, 11:38 AM	#3
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	How much current are you after ?

12th January 2011, 11:58 AM	#4
madtecchy diyAudio Member Join Date: Dec 2010 Location: wigan	Hi andy it is just a product of my thought . i like to salvage parts from old discarded electronic equipment and this would be a way to use single winding transformers to power dual rail amplifiers. im guessing the current would be shared between the rails so maybe less than half the current per rail. And DF96 do you think it would have approx double the ripple ????. i will dig out my old scope later and have a look at this circuit when it has a load attached. Regards Mark

12th January 2011, 12:18 PM	#6
madtecchy diyAudio Member Join Date: Dec 2010 Location: wigan	Hi Andy Thankyou for the alternatives i should of said i like the idea and topology of keep it simple stupid.

12th January 2011, 12:42 PM	#7
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	Realistically though, WEO the SMPS approach you are not going to get any appreciable current out of a pseudo 0V approach.

12th January 2011, 03:02 PM	#10
madtecchy diyAudio Member Join Date: Dec 2010 Location: wigan	Andy are you a fan of smpsu's. I dont think this circuit will have too many problems supplying current. however im sure it will need lots of smoothing. I had a look at the cirrus link yes they are zener's and yes it is not a rectifier. regards