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 30th December 2006, 03:20 AM   #1
diyAudio Member
 
Join Date: Feb 2002
Location: Canada
Default Brief Description of Linear vs. SMPS

Taken from Audio Asylum and posted here for the benefit of novices like myself!

Quote:
First, a review of a "linear" power supply. A linear supply or regulator produces an output voltage which is less than the input voltage. This is done by dropping the difference voltage across a pass transistor, and generating heat. A linear regulator with a 5 volt 1 amp output, and a 12 volt input dissipates 7 volts (12 minus 5) times 1 amp or 7 watts, in addition to power used to drive the internal circuitry. In this example, the efficiency upper limit is 5/12 or 0.417 (41.7%). When the input voltage is the AC mains, 115 or 230 volts RMS, 50 or 60 Hz, a transformer is needed to provide electrical isolation, per safety agency requirements (UL, CSA, VDE, etc.). Since the transformer core flux has a frequency of 50 or 60 Hz, the core must be quite large (and heavy) in order to prevent magnetic saturation. After the transformer, there is a full wave rectifier and a bank of filter capacitors, followed by the linear regulator circuit. The linear regulator must have an input greater than the output. At minimum line, 85, 90, or maybe 100 volts RMS, the rectified and filtered voltage at the regulators input must be above the desired output voltage. At nominal line of 117 volts, the voltage at the input of the regulator is quite a bit above the minimum needed. This extra voltage multiplied by the current is equal to the additional power that must be dissipated. At high line, 127 or 132 volts RMS, more heat is generated.
A switch mode power supply, herein called SMPS, regulates by switching the transistor between saturation (fully on), and cutoff (fully off). When the transistor turns on, energy is delivered to an inductor, and in some cases to the output capacitor and load. When the transistor turns off, the inductor's stored energy is delivered to the output filter cap and load. The transistor is operating either at full current and minimum voltage, or full voltage and minimum current, which results in low amounts of wasted power. Efficiencies of SMPS's nowadays are 80 to 95% and even higher in some cases.Typical switching frequencies are anywhere from 25 kHz to over 1 MHz, with 50 kHz to 250 kHz the range I usually use when designing an SMPS. In an offline SMPS (ac mains), the transformer needed for isolation is operating with a core flux in the frequency range mentioned above, much, much higher than 50 or 60 Hz. This results in a core much smaller and lighter. Also, since much less heat is generated due to high efficiency, smaller parts and smaller heat sinks (sometimes the pc board alone can act as a sufficient heat sink) can be used.
Another advantage to an SMPS is that the input voltage does not have to be above the output. While a linear regulator can only step down, a switcher can step up or down. Some circuits (buck-boost, SEPIC, isolated flyback) can do both, delivering a steady output voltage from an input less than or greater. A common boost circuit can be found in a photoflash unit which converts a 3 or 6 volt input (2 or 4 1.5 volt "AA" cells) to 400-500 volts to power the flash tube. A linear regulator cannot boost.
The down side to an SMPS is that it is very noisy compared to linear. Also, the cost is generally higher, but the cost differential for an SMPS vs. linear is not as large as it used to be. Substantially more parts are needed for an SMPS.
This is only a brief overview, not an exhaustive analysis, but I hope it helps. Best regards.

Claude
Regards,
Dan
  Reply With Quote
Old 30th December 2006, 01:49 PM   #2
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
A 50/60Hz transformer whose secondary windings are rectified and filtered with capacitors *MUST* be considered a switching mode power supply too. It's a low frequency SMPS but it has all the parasitistic elements present in any high frequency SMPS and the same ability to radiate and output "noise" and to disturb other circuits. The only difference is the speed and the rate at which things happen.

Go to the chip-amp or the solid state forums and you will see many threads dealing with buzz and humm problems caused by 50/60Hz transformer, diode and capacitor arrangements. That's plain low-frequency SMPS noise
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 30th December 2006, 02:31 PM   #3
diyAudio Member
 
Join Date: Feb 2002
Location: Canada
That's why we use these high quality voltage regulators (i.e. ALWSR, Audiocom, Tent Labs) on these linear supplies. It helps eliminate such noise. Unfortunately I have a SMPS I'm trying to upgrade and it has a some unique challenges in the pursuit of eliminating this 'noise'.

Regards,
Dan
  Reply With Quote
Old 30th December 2006, 03:24 PM   #4
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
I can assure that SMPS can be made really really quiet, but it's something tricky to achieve, it's like reducing humm and buzz below the noise floor in an amplifier or pre-amplifier with a conventional power supply...
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 30th December 2006, 06:48 PM   #5
diyAudio Member
 
Join Date: Feb 2002
Location: Canada
I'm familiar with the principles involded in reducing noise in a linear power supply. But not so for SMPS. If you have any hints I'm all ears.

Regards,
Dan
  Reply With Quote
Old 9th January 2007, 07:46 PM   #6
diyAudio Member
 
N-Channel's Avatar
 
Join Date: Mar 2003
Location: Sol System
Send a message via AIM to N-Channel
Dan,

Check out almost any thread in the Power Supplies forum that EVA has posted to. She is extremely knowledgeable, and a better approach would be look them over. LOTS of good, useful stuff. Also, there are a number of other talented folks in this Forum.

Hope this helps,

Steve,
  Reply With Quote
Old 10th January 2007, 08:45 PM   #7
diyAudio Member
 
Join Date: Dec 2006
Quote:
Originally posted by Eva
A 50/60Hz transformer whose secondary windings are rectified and filtered with capacitors *MUST* be considered a switching mode power supply too. It's a low frequency SMPS but it has all the parasitistic elements present in any high frequency SMPS and the same ability to radiate and output "noise" and to disturb other circuits. The only difference is the speed and the rate at which things happen.
Where is the switching in a linear power supply? The AC is generated in the power plant by induction, there's no switching (in the sense that switches are turned on and of). I thought that this was essentially the difference between linear and switch mode, not parasitic elements, radiation or noise...
Also, even for a novice (like I still consider myself), I don't think the article posted by dantwomey is very clarifying. It is more about regulation efficiency.
Am I right?

Sambal
  Reply With Quote
Old 10th January 2007, 08:59 PM   #8
diyAudio Member
 
Join Date: Dec 2006
Quote:
Originally posted by Sambal Oelek

...there's no switching (in the sense that switches are turned on and of). I thought that this was essentially the difference between linear and switch mode
In addition: an SMPS is always a DC-DC converter (or contains a DC-DC converting circuit). In a linear supply there is no DC-DC conversion
  Reply With Quote
Old 11th January 2007, 08:40 AM   #9
diyAudio Member
 
megajocke's Avatar
 
Join Date: Jan 2003
Quote:
Originally posted by Sambal Oelek


Where is the switching in a linear power supply? The AC is generated in ...

Sambal

The diodes in the rectifier switch.
  Reply With Quote
Old 11th January 2007, 12:14 PM   #10
diyAudio Member
 
Join Date: Feb 2002
Location: Canada
I'm looking at replacement diodes. See my new post, "Upgrading My SMPS For Audio Use"

Regards,
Dan
  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
System Pictures & Description Serow Multi-Way 2528 Today 03:54 AM
SMPS inverter complete design and description drwaseerwp Power Supplies 0 19th May 2008 07:49 PM
More situation description jlg4104 Tubes / Valves 1 2nd December 2002 02:13 PM


New To Site? Need Help?

All times are GMT. The time now is 03:44 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