Capacitance Multiplier on SMPS

jkeny · 29th May 2008, 08:25 AM

I posted this in the Class-D area but no replies - it's probably more suited to this forum!

Has anybody tried this to reduce HF noise on SMPS. AFAIK cap mult acts as an inductor & so HF is attenuated more. Would this be a good way of removing the HF spikes on these PS?

I'm thinking of improving my CD/DVD players as well as a digital amp that use SMPS

The idea and some oscilloscope shots are here as part of an interesting discussion on how to improve 3 pin voltage regulators: http://www.acoustica.org.uk/t/3pin_reg_notes2.html

EWorkshop1708 · 29th May 2008, 01:48 PM

Why not? On certain audio circuits like preamps or opamps in general, it's good to have a lot of filtering. IMO you can never have too much filtering.

jkeny · 29th May 2008, 02:08 PM

Yea, my simplistic thinking on this was that most, if not all, of the noise on the supply of a SMPS tends to be well outside the audio band up around the switching freq & this is where a gyrator or cap multiplier has it's biggest attenuation.

I just wanted to check out with some of the SMPS experts here if there is any gotchas before I try it out on real equipment!

megajocke · 31st May 2008, 11:49 PM

I wouldn't expect a capacitance multiplier to have very good attenuation at the >1MHz frequencies of interest. It should have the same problem as the 3 terminal regulators tested in that link.

And why would you need it? The cap values required are small. An RC or LC filter will work much better.

Tolik · 10th June 2008, 09:03 PM

Else check AVX multilayer ceramic caps 20..50..60uf, specially designed for noise attenuation in SMPS. These can be found at Digy Key.

cerrem · 11th June 2008, 08:36 AM

Quote:

Originally posted by jkeny
I posted this in the Class-D area but no replies - it's probably more suited to this forum!

Has anybody tried this to reduce HF noise on SMPS. AFAIK cap mult acts as an inductor & so HF is attenuated more. Would this be a good way of removing the HF spikes on these PS?

I'm thinking of improving my CD/DVD players as well as a digital amp that use SMPS

The idea and some oscilloscope shots are here as part of an interesting discussion on how to improve 3 pin voltage regulators: http://www.acoustica.org.uk/t/3pin_reg_notes2.html

EMC radiated emissions is a royal pain to tackle with SMPS...
I have designed PWM chips with dither in the clock to spread spectrum the noise, thus lowering the amplitudes of the noise...
The other option is to use quasi resonant circuit...

cerrem

cerrem · 11th June 2008, 08:41 AM

Quote:

Originally posted by jkeny
I posted this in the Class-D area but no replies - it's probably more suited to this forum!

Has anybody tried this to reduce HF noise on SMPS. AFAIK cap mult acts as an inductor & so HF is attenuated more. Would this be a good way of removing the HF spikes on these PS?

I'm thinking of improving my CD/DVD players as well as a digital amp that use SMPS

The idea and some oscilloscope shots are here as part of an interesting discussion on how to improve 3 pin voltage regulators: http://www.acoustica.org.uk/t/3pin_reg_notes2.html

EMC radiated emissions is a royal pain to tackle with SMPS...
I have designed PWM chips with dither in the clock to spread spectrum the noise, thus lowering the amplitudes of the noise...
The other option is to use quasi resonant circuit...

cerrem

star882 · 11th June 2008, 01:22 PM

Quote:

Originally posted by cerrem

EMC radiated emissions is a royal pain to tackle with SMPS...
I have designed PWM chips with dither in the clock to spread spectrum the noise, thus lowering the amplitudes of the noise...
The other option is to use quasi resonant circuit...

cerrem

Isn't the simplest solution just enclosing the power supply in a metal box?

Eva · 11th June 2008, 02:59 PM

EMI is mostly radiated by external wiring so metal enclosures are not of great help.

The most useful filtering is common-mode and its purpose is to keep input and output grounds at the same RF potential. Then differential-mode filtering attenuates the remaining RF components before they reach the wiring.

A capacitance multiplier is mostly useless in comparison with a LC filter.

29th May 2008, 08:25 AM	#1
jkeny Banned Join Date: Feb 2007 Location: Dublin	Capacitance Multiplier on SMPS I posted this in the Class-D area but no replies - it's probably more suited to this forum! Has anybody tried this to reduce HF noise on SMPS. AFAIK cap mult acts as an inductor & so HF is attenuated more. Would this be a good way of removing the HF spikes on these PS? I'm thinking of improving my CD/DVD players as well as a digital amp that use SMPS The idea and some oscilloscope shots are here as part of an interesting discussion on how to improve 3 pin voltage regulators: http://www.acoustica.org.uk/t/3pin_reg_notes2.html

10th June 2008, 09:03 PM	#5
Tolik diyAudio Member Join Date: Mar 2007	Else check AVX multilayer ceramic caps 20..50..60uf, specially designed for noise attenuation in SMPS. These can be found at Digy Key. __________________ Êòî óìååò äåëàòü - äåëàåò. Êòî íå óìååò - ó÷èò. Õ.Ë. Ìåíêåí. Those who can, do. Those who can't, teach. Those who can't teach, do research. H.L. Mencken

11th June 2008, 02:59 PM	#9
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	EMI is mostly radiated by external wiring so metal enclosures are not of great help. The most useful filtering is common-mode and its purpose is to keep input and output grounds at the same RF potential. Then differential-mode filtering attenuates the remaining RF components before they reach the wiring. A capacitance multiplier is mostly useless in comparison with a LC filter. __________________ I use to feel like the small child in The Emperor's New Clothes tale

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Capacitance Multiplier PSU	Ted205	Chip Amps	3	2nd March 2009 01:27 PM
Capacitance Multiplier on SMPS	jkeny	Class D	3	29th May 2008 07:15 PM
Capacitance Multiplier	Kinnja	Solid State	2	13th January 2008 08:12 PM
Capacitance Multiplier for A5?	siouxiebuff	Pass Labs	3	21st January 2006 04:27 PM


	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

29th May 2008, 01:48 PM	#2
EWorkshop1708 diyAudio Member Join Date: Nov 2004 Location: Florida	Why not? On certain audio circuits like preamps or opamps in general, it's good to have a lot of filtering. IMO you can never have too much filtering.

29th May 2008, 02:08 PM	#3
jkeny Banned Join Date: Feb 2007 Location: Dublin	Yea, my simplistic thinking on this was that most, if not all, of the noise on the supply of a SMPS tends to be well outside the audio band up around the switching freq & this is where a gyrator or cap multiplier has it's biggest attenuation. I just wanted to check out with some of the SMPS experts here if there is any gotchas before I try it out on real equipment!

31st May 2008, 11:49 PM	#4
megajocke diyAudio Member Join Date: Jan 2003 Location: Solna	I wouldn't expect a capacitance multiplier to have very good attenuation at the >1MHz frequencies of interest. It should have the same problem as the 3 terminal regulators tested in that link. And why would you need it? The cap values required are small. An RC or LC filter will work much better.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read