Talk:Switched-mode power supply

Bold text== Initial discussion == Corrected rectifier section: Not all rectifiers are voltage doublers. This is clearly explained further down. Also current pulses at peaks of AC voltage cause high frequency not low frequency harmonics.

Headline text

deleted the last line stating that computer PSU's are configured as voltage doublers

Mains Frequency vs Isolation

Why does it say linear power supplies only operate at 50/60 Hz if they are isolating? Could someone please explain this statement B4 I attempt correction Light current 19:33, 8 August 2005 (UTC)[reply]

The frequency from which Linear Power supplies operate is constrained by the design of the power transformer. If you wanted to build one with a 400 Hz transformer, there is nothing to prevent it. Domestic SMPS supplies are only rated at 50/60 Hz. In practice, because the input circuit is a straight rectifier/reservior capacitor, they will operate quite happily off a much wider range of frequencies. We use standard SMPS supplies at 400 Hz. Because of the rectifier, they will also operate from DC.

If the article says that, it's wrong. Linear regulators are dc-to-dc devices and so the question of "input frequency" is moot. Linear power supplies, on the other hand, usually have an ac isolation transformer as their first stage, so they'll operate over whatever frequency range is supported by their input transformer and the bulk storage capacitors that follow the rectifier stage. Atlant 00:01, 9 August 2005 (UTC)[reply]

I have removed the ref to isolating transformers.Could Atlant and others please now look at the page to see if it makes sense to them. THanks Light current 19:59, 9 August 2005 (UTC)[reply]

Advantages of SMPS over linear

I dont think that SMPS are neccesarily more expensive to build what with the automatic placement of components used these days. In fact SMPS are probably now the cheapest supplies you can buy (watt for watt). Please comment. I would like to remove this inaccuracy. Any body object? Light current 20:06, 9 August 2005 (UTC)[reply]

I object! :-) There's nothing cheaper in the world than a three-terminal fixed linear regulator. One part, job done. (Oh, okay, some regulators expect a bypass cap or two.) With an SMPS, at a minimum, you have to overcome the cost of the inductor, so it's only above some critical power level that the SMPS becomes cheaper. (I don't know what this power level would be; it probably depends on whether your circuit board can act as an adequate heat sink for the three-terminal regulator.)

Atlant 23:48, 9 August 2005 (UTC)[reply]

No, I thought the article was comparing complete SMPS with complete linear power supplies with mains transformer, rectifier, smoothing caps and regulation circuit. Do you still say a switcher is more expensive if made in China??:-)Light current 23:54, 9 August 2005 (UTC)[reply]

If the article is describing exclusively mains-powered power supplies, then it should be expanded as I think most engineers would also consider (for example) an "eighth-brick" dc-to-dc converter as a power supply as well. But coming back to your point, I suspect there's not much price difference between minimalist Chinese-built linear power supplies (as exemplified by some high-end "power bricks" that include regulation) and SMPSs.

Atlant 00:36, 10 August 2005 (UTC)[reply]

This part of the article doesn't seems really fair to me: it considers "good" linear psu, the effects of "malfunctionning" switching PSUs... The last item is not fair either: the bad power factor of a linear PSU is not considered as a problem, whereas 0.6 for a switching PSU is unacceptable.CyrilB 11:27, 25 January 2006 (UTC)[reply]

Chopper Timing

How is this done? Oscillator + discrimnator? For variable voltage supplies I would guess a digital timer would be wise? At least for high voltage the high voltage can not be measured directly and thus not fast enough to detoriate the stabilty of a direct feedback ( 110kV transformer for a klystron). --Arnero 19:56, 31 January 2006 (UTC)[reply]

Contradiction in the article

In the beginning of the article it is said that "Switching regulators are used as replacements for the linear regulators when higher efficiency, smaller size or lighter weight are required. They are, however, more complicated and more expensive, their switching currents can cause noise problems if not carefully suppressed, and simple designs may have a poor power factor" , suggesting that SMPS may be noisier than linear, and that the noise of a SMPS must be carefully supressed. Compare this to what is later said: " Audio noise. Linear PSUs typically give off a faint, low frequency hum at mains frequency, but this is seldom audible. (The transformer is responsible.) SMPSs, with their smaller transformers, are not usually audible (unless they have a fan, in the case of most computer SMPSs). A malfunctioning SMPS may generate high-pitched sounds, since they do in fact generate acoustic noise at the oscillator frequency.". This suggests the opposite: that SMPS are usually more quiet, unless they are malfunctioning. I don't know which (the first or the second quote) is true, so I can't correct the article myself. - Jorge 09:31, 17 May 2006 (UTC)[reply]

The comparison between linear and switching PSU in this article is biased anyway (as I mention above, this compares malfunctioning SMPS with good Linear PSU...). It looks to me that this article is oriented towards audio electronics, which is a domain where "old fashion" electronics may be of higher interest than in any other electronic domain. I'll try to improve the article (if I can), but concerning your question, the first citation adresses electromagnetic noise, whereas the second is about acoustic noise. I don't see much contradiction here. -- CyrilB 15:34, 20 May 2006 (UTC)[reply]

I didn't realise that. It could be more clear. Jorge 01:02, 23 May 2006 (UTC)[reply]

This makes no sense

In early 2006 even very low power linear regulators became more expensive than SMPS when the cost of copper and iron used in the transformers increased abruptly on world markets.

Should be clarified more.... not all linear regulators use a transformer

                  RAJ SOROUT

smps is a device mainly convert AC to DC —Preceding unsigned comment added by 203.115.104.44 (talk) 07:25, 14 September 2007 (UTC)[reply]

New (improved?) intro

I thought the intro was redundant, so I changed it to remove excess information and simplified it. Please edit or revert if you think these changes do not improve the article. SparhawkWiki 15:10, 17 September 2007 (UTC)[reply]

Topologies

What is the difference between "Full-Bridge Topology" and "Push-Pull Topology" that are listed in article? I think they are same.

See: http://schmidt-walter.fbe.fh-darmstadt.de/smps_e/smps_e.html —Preceding unsigned comment added by 130.230.1.90 (talk) 18:31, 28 September 2007 (UTC)[reply]

Comparison section is in some parts confusing.

Some sections in the comparison section makes little sense. It needs some clarification. —Preceding unsigned comment added by Ginbot86 (talk • contribs) 22:44, 14 April 2008 (UTC)[reply]

Losses?

This is probably a stupid question, but I have a 200W ATX power supply at home, and it claims to need 5A at 120V, which is 600W, which equates to about 33.33333333 (etc.) percent efficiency. I thought SMPS's were supposed to be more efficient than that. Aren't linear power supplies more efficient than 33% (in which case something about this inefficiency should be included in the article) or am I just doing the math wrong? Ilikefood (talk) 13:53, 10 July 2008 (UTC)[reply]

Five amps is almost certainly the maximum rated power consumption, which occurs for a split second at turn on. Do you feel a 400 watt heat blast coming out of the supply? Monitor it with a wattmeter to find out what it actually draws. It varies in proportion to the load, but probably is over 70% efficient. In my experience, the article's efficiency numbers are pessimistic. Monitoring mine through the UPS interface suggests its efficiency is around 90%, but it's hard to measure all the output currents. —EncMstr (talk) 15:58, 10 July 2008 (UTC)[reply]

incorrect efficiencies listed in the table

The efficiencies noted in the table are too listed to low; 69% for full bridge? 75% for buck? In fact, these converters when properly designed, perform typically better than 90%, including EMI filters.

TBH the whole Typical Efficiency column should be removed, its completely bogus to say 1 topology will typically be X efficiency. In theory using todays parts you could easily make 90% efficiency or better from each of the topology's. The typical voltage in is just as bad, voltage in capabilities are determined by parts at hand and design requirements of the power supply. Some will do better at lower or higher voltages than others, but arbitrary numbers are bogus. Ile review the talk page and then remove/edit this.Eadthem (talk) 21:06, 18 June 2009 (UTC)[reply]

capacitors bridging the primary and secondary sides

This article briefly mentions "capacitors bridging the primary and secondary sides of the power supply."

At first I thought this was a misunderstanding -- perhaps someone saw such a capacitor in a SPICE circuit diagram, representing stray parasitic capacitance, and incorrectly thought it represented a real physical component.

However, I see that figure 35 of AN920: "Theory and Applications of ... Switching Regulator Circuits (Alberkrack 2006) does show one such capacitor. That capacitor connects one pin from the 115 VAC power plug to the (otherwise isolated) output "return" terminal (midway between the output +12 and output -12 terminal).

Why would a designer would carefully isolate the primary from the secondary side, and then link them back together again with one or more capacitors?

What would happen if some manufacturer simply left out this linking capacitor?

What purpose does this capacitor have? --68.0.124.33 (talk) 04:06, 3 August 2008 (UTC)[reply]

I think it's to sink RF harmonics and to provide a RF ground —Preceding unsigned comment added by 124.177.184.228 (talk) 06:30, 18 August 2008 (UTC)[reply]

These capacitors are to do with RF filtering. They do give the strange behaviour that the output from these supplies floats at about half the mains input voltage if there is no earth path (It can be measured with a standard meter). The charge on the capacitors also gives a small spark if the output connector is engaged with something that is earthed (US: Grounded). 20.133.0.13 (talk) 14:04, 28 October 2008 (UTC)[reply]

Efficiency figures

I think these are potentially misleading, particularly with regard to the efficiency of the split-pi converter relative to the other types. These figures need to be qualified with respect to:

Voltage/power range
Devices used
Passive or synchronous rectification
EMI considerations - is this for converters contained in shielded boxes with expensive input/output filters or otherwise?
Resonant/non-resonant?

As far as I can tell there is no inherent reason for the split-pi converter to be significantly more efficient than synchronous buck/boost converters using similar power devices. If anything slightly worse efficiency would be expected since the upper device on the output side is always conducting, contributing I²R losses over a synchronous buck or boost converter operating under the same conditions, using the same devices.

agreed, the split-pi seems to only have listed applications in one area, and one cherry-picked case is used. really, the table is fairly lacking. if you want to include more obscure topologies or combinations, you'd have quite a few more. 2-transistor flyback isn't unheard of. there are some isolated boost converters and autoformer based converters that could be added. likewise things like the push-pull being used for 100W+ isn't really accurate, as there are examples of its usefulness in sub-watt applications. —Preceding unsigned comment added by 174.18.145.83 (talk) 01:39, 2 June 2009 (UTC)[reply]

Switch mode power supply reliability versus Linear

Many computer power supplies fail. More parts equal more areas for failure.

History

I was hoping to see something about the history of switched mode power supply development, but there's no mention of it.Sadg4000 (talk) 09:49, 27 May 2009 (UTC)[reply]