Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th April 2009, 05:52 AM   #1
diyAudio Member
 
Join Date: Apr 2008
Default Need help with voltage doubler

Alright, I'm working on a class A SE mosfet amplifier. The psu transformer i have is center tapped, and capable of 8 amps at 24v ac. The amplifier is going to use a dual supply, with each channel drawing around 1.75A each constant. What would be a suitable configuration to boost my rails? I'm shooting for about 20~30v per rail. Could I use a conventional doubler with just the center point of my caps as ground? For smoothing I was going to use a capacitance multiplier if that makes a difference.
  Reply With Quote
Old 19th April 2009, 12:23 PM   #2
diyAudio Member
 
Join Date: May 2006
Do you mean this circuit?

Click the image to open in full size.

That would be the easiest option in your case, it gives ~33V peak.

You need plenty of capacity for filtering however, since in effect you have two half-wave rectifiers. See attached screenshot - with 47000uF (47mF), the ripple is about 2V p-p.

Your capacitance multiplier can regulate that down to ~30V nicely.
Attached Images
File Type: png r1_sim.png (18.5 KB, 140 views)
__________________
--WD
  Reply With Quote
Old 19th April 2009, 06:23 PM   #3
diyAudio Member
 
Join Date: Apr 2008
Alright! Thank you for the reply. So That's what I think I'll do then. Since my transformer is center tapped, do I just leave that tap alone?
  Reply With Quote
Old 19th April 2009, 09:05 PM   #4
diyAudio Member
 
Join Date: May 2006
Yes, no use for the center tap.
__________________
--WD
  Reply With Quote
Old 20th April 2009, 09:32 AM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Default Re: Need help with voltage doubler

Quote:
Originally posted by Lingwendil
... a class A SE mosfet amplifier............... The amplifier is going to use a dual supply, with each channel drawing around 1.75A each constant...................... Could I use a conventional doubler with just the center point of my caps as ground?
your SE mosfet amplifier is very unlikely to draw constant current from it's dual polarity supply rails. Almost all topologies of ClassA modulate the current in the supply rails to follow the output current.

High currents do not suit voltage doublers. A voltage doubler is ideally suited to the tiny currents required to power the voltage amplifier stage of a power amp or for pre-amps, not the high current demands of power amps. The ripple on the supply after the doubler will be as bad as a half wave rectified PSU and the voltage droop as load current increases will be worse than a half wave rectified supply.
__________________
regards Andrew T.
  Reply With Quote
Old 21st April 2009, 11:02 AM   #6
diyAudio Member
 
Join Date: May 2006
Default Re: Re: Need help with voltage doubler

Quote:
Originally posted by AndrewT
High currents do not suit voltage doublers. A voltage doubler is ideally suited to [...] tiny currents
Since his Class-A amp will draw <2A, we are not talking about *high* currents here. The dual half-wave "doubler" is definitely not only for "tiny" currents - you have one of these in the input of every PC power supply that has a 115/230V switch, whether it handles 250 or 600 Watts (5.2A @ 115V!)

Of course, switchers work much better with the high ripple than linears. No question, two transformers would be better, but with enough capacity and a regulator, a half wave rectifier can also do the job. You just need to calculate the effects and decide whether the result is acceptable.
__________________
--WD
  Reply With Quote
Old 22nd April 2009, 12:15 AM   #7
diyAudio Member
 
Join Date: Apr 2008
Well, since I have the parts on hand I figure I may as well give it a try. This is for a junk-box/ found parts project anyway, so if it has small flaws I don't mind too much. I just would like to get a bigger swing from my amp, and figure'd it'd be worth a try.


The circuit is basically a beefed up oversized Szekeres buffer. No gain, no problem, as I have a nice tube preamp. As is, the psu is unregulated or filtered, just a pair of 33000uF across my rails. Hum is just barely audible. my rails sit at 14.65v each under load, with or without signal. As of this writing, idle current is 1.25A per channel via a LM317 CCS. Would using the doubler give me al least 24v rails under these conditions, all else remaining equal?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
All tube voltage doubler Steven-H Tubes / Valves 16 8th July 2011 12:02 PM
Voltage Doubler jwatts Tubes / Valves 3 2nd January 2009 12:13 AM
Voltage doubler question Ryssen Tubes / Valves 25 14th October 2006 06:22 PM
Voltage doubler Baard Solid State 28 17th January 2005 04:46 AM
Voltage Doubler Problem runeight Tubes / Valves 10 7th April 2004 04:16 AM


New To Site? Need Help?

All times are GMT. The time now is 12:11 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2