Capacitance Multiplier question - diyAudio
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 17th May 2012, 08:01 PM   #1
diyAudio Member
 
tom42107's Avatar
 
Join Date: Feb 2010
Default Capacitance Multiplier question

I breadborded the capacitance multiplier posted below. I used a transformer with a 36v secondary but I need 24v out of the multiplier. I changed the top 430R resistor to different values until I got ~24v. The value ended up being 10K. The voltage drop across each 10K resistor is ~25V and about .22mA. Forget to mention, I only used the top half because I only needed a mono-polar power supply. I did use a full wave bridge rectifier. That is as far as I got. I guess my question, what are the pros and cons of what I did. I only have a DMM to measure voltage out. Is it efficient or wasteful? Still learning power supplies. Everything else on the schematic stayed the same except the 430R.

Tom
Attached Images
File Type: gif jlhcapmultfig3.gif (6.0 KB, 359 views)
  Reply With Quote
Old 17th May 2012, 08:28 PM   #2
diyAudio Member
 
Join Date: Mar 2003
Location: Haarlem, the Netherlands
The time constant of the two resistors with the 1000 uF capacitor will be as large as 5 seconds. That is good for ripple rejection, but it also means that your supply will need dozens of seconds to settle.

Regarding efficiency: a bit more than half the power will be converted into heat in the pass transistor, as it would in a normal series regulator with 50 V input and 24 V output voltage. If you don't want that, you need a lower secondary voltage of the transformer.
  Reply With Quote
Old 17th May 2012, 09:23 PM   #3
diyAudio Member
 
Join Date: Nov 2008
Location: Oakmont PA
Is there a reason why you aren't using a zener diode?
  Reply With Quote
Old 18th May 2012, 02:21 AM   #4
kp93300 is offline kp93300  Malaysia
diyAudio Member
 
Join Date: Mar 2007
Hi
Is this circuit suitable for small ampere requirement such as a preamp and +/_ 12 V dc ?
kp93300
  Reply With Quote
Old 18th May 2012, 03:01 AM   #5
diyAudio Member
 
tom42107's Avatar
 
Join Date: Feb 2010
Quote:
Originally Posted by simon7000 View Post
Is there a reason why you aren't using a zener diode?
No, no reason. To be really honest, I'm not sure where the zener would go or the reason for it. Could you help me with it.

Quote:
Originally Posted by kp93300 View Post
Hi
Is this circuit suitable for small ampere requirement such as a preamp and +/_ 12 V dc ?
kp93300
kp93300, this is the simple capacitance multiplier described in the Class A website, The Class-A Amplifier Site - The Capacitance Multiplier, for the JLH amp.

Tom

Last edited by tom42107; 18th May 2012 at 03:05 AM.
  Reply With Quote
Old 18th May 2012, 11:30 PM   #6
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
Adding a zener diode (or two, as here) helps extend the voltage regulation down to true DC; and above that they would force a fixed DC voltage output, because zeners form convenient voltage references.

The zeners would go in the place of R3 and R4. Since you want 24v dc out, you need a zener of 24+ the Vbe of the pass transistor (0.7v). Funnily enough, that means a nominal 24v zener diode will work fine in both places - because the actual voltage on each will rise a touch when you force some current through them, they are not perfect and do have a small amount of dynamic impedance.

So - with zeners in place - you should size R2 and R3 to pass 5-10mA through each zener. For example, 35vAC secondary probably means you have about +/-45VDC under load appearing on the input. So R2 and R3 each wants to be about (45-24)= 20v/5mA = 4kohms. 3K9 or 4K7 are standard values and close enough.

Each zener will then dissipate about 10mA * 24v = 240mw. Use 1W rated parts, minimum, for reliability (1.3w are next common standard size - ideal)

Do leave C2/ C3 in place.

If you want even more filtering you can then introduce a small resistance between the R2/zener junction and C2- base junction (and same for the other side) of say 22-100R. With C2/ C3 as given that will put a brutal filter on the already-negligible noise contributed by the zeners (f = 1/ 2*pi*R*C, so just 22R / 1000uF means about 7Hz low pass!)

You should get a very quiet supply for very little effort or cost
  Reply With Quote
Old 19th May 2012, 12:53 AM   #7
kp93300 is offline kp93300  Malaysia
diyAudio Member
 
Join Date: Mar 2007
Hi Martin
thanks for your input that i am interested to implement but i am a bit confused. I would be very happy if you can provide a schematic of your suggestions.
I do not want to impose on you

thanks
kp93300
  Reply With Quote
Old 19th May 2012, 01:20 AM   #8
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
No need for a diagram, really: it would be exactly the same as the diagram in the very first post in this thread , but with a 12v or 13.2v zener in the place of each of R3 and R4. Either value will work (and in any case, relying on an exact DC supply voltage is lousy practise for whatever follows. )


- So, both zeners to have the anode towards the+ve rail ( ie the 'upper' one to have anode to the junction of R1/C3; and the -ve zener to have its anode to 0v, and cathode to the junction of C4/R2)

Just have a go
  Reply With Quote
Old 19th May 2012, 04:43 AM   #9
diyAudio Member
 
tom42107's Avatar
 
Join Date: Feb 2010
Martin, thanks for such a helpful post. I'm off to buy some zener's.

Tom
  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
2SC5200 for Capacitance Multiplier shaan Solid State 6 6th May 2010 12:41 PM
Capacitance multiplier question philpoole Power Supplies 25 20th February 2008 09:02 PM
Capacitance Multiplier Kinnja Solid State 2 13th January 2008 08:12 PM
Capacitance multiplier problem Kari Solid State 7 5th February 2005 06:24 PM


New To Site? Need Help?

All times are GMT. The time now is 09:12 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