Proper way to adjust output voltage

bvtrinh

Member
2014-09-06 1:59 am
Hello, I would like to build a LCLC-PSU and was wondering what the proper way of adjusting the output voltage? I was initially thinking of using a trimpot but I know the excess voltage needs to be disappated somehow, which is usually in the form of heat. Any help or articles would be greatly appreciated.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
LCLC PSU

Capture.GIF
 

bvtrinh

Member
2014-09-06 1:59 am
Yes

I assume he meant a choke input PSU with choke smoothing too. I can't attach any other meaning to LCLC PSU.

Yes, this is what I mean. I have attached a diagram as well as something I built. Without a load, I can easily and accurately adjust the output voltage with a trimpot. Once I attach it to a load, I will monitor the voltage and temperature.
 

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wg_ski

Member
2007-10-10 5:21 pm
Yes, this is what I mean. I have attached a diagram as well as something I built. Without a load, I can easily and accurately adjust the output voltage with a trimpot. Once I attach it to a load, I will monitor the voltage and temperature.

I don't see a way to adjust that with a trimpot. That "LCLC" is just a 2-section choke input filter.

With that level of filtering you might be able to use SCRs for D1 and D2 and adjust the phase angle. Old-school HP bench supplies did this, but they usually had a post-regulator to clean it up. I'm assuming you are using Two LC sections to get the hum and noise down to microvolt levels without resorting to nasty "IC's" - which would make any sort of adjustable circuit self-defeating.
 

bvtrinh

Member
2014-09-06 1:59 am
I don't see a way to adjust that with a trimpot. That "LCLC" is just a 2-section choke input filter.

With that level of filtering you might be able to use SCRs for D1 and D2 and adjust the phase angle. Old-school HP bench supplies did this, but they usually had a post-regulator to clean it up. I'm assuming you are using Two LC sections to get the hum and noise down to microvolt levels without resorting to nasty "IC's" - which would make any sort of adjustable circuit self-defeating.

Thank you for your response. I have to admit that my knowledge in circuits is very basic. I am exploring this power supply because it seems simple enough and from what i've read, works well. It is silent when I test it without a load. I do not have an oscilloscope to test it to that degree.
 

rayma

Member
2011-04-29 8:37 pm
No, I'm planning on using it to supply 12v to an ATX control board for a dedicated
computer based music server. I also will be using a similar LCLC setup for the 5v and 3.3v.

Then this would substitute for a standard computer power supply, in hopes of having lower noise?
The control boards likely require tighter voltage regulation than possible with a passive circuit like this.
How about standard linear regulated voltage supplies instead? Those are readily available, as kits or built.
With power transformers, three of these boards, 12v, 5V, and 3.3V would work. Depending on the required
currents, you may need separate power transformers with different secondary voltages for each, to reduce
power loss in the regulators. You could even keep the LC filtering on each of the voltage outputs, if desired.
An example: http://www.ebay.com/itm/AC-DC-12V-2...352740?hash=item1a0ca5f624:g:ApMAAOSwqYBWoMib
 
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bvtrinh

Member
2014-09-06 1:59 am
Another option

Then this would substitute for a standard computer power supply, in hopes of having lower noise?
The control boards likely require tighter voltage regulation than possible with a passive circuit like this.
How about standard linear regulated voltage supplies instead? Those are readily available, as kits or built.
With power transformers, three of these boards, 12v, 5V, and 3.3V would work. Depending on the required
currents, you may need separate power transformers with different secondary voltages for each, to reduce
power loss in the regulators. You could even keep the LC filtering on each of the voltage outputs, if desired.
An example: AC DC 12V 24V LT1083CP HiFi Linear Regulator Voltage Adjustable Power Supply Kit | eBay

That is definitely another option. Thank you for that!
 

rayma

Member
2011-04-29 8:37 pm
That is definitely another option. Thank you for that!

Remember that each regulator's input voltage must be carefully chosen to prevent dropping out,
and also to limit excessive power dissipation in the regulator. There may be a single commercial
line operated supply available with all 3 voltages and adequate current if you look.
 
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