Switched mode supply - Page 1
Forum section: electronics / beginners

author: abzoli
author_rank: Newbie
timestamp: March 24, 2012, 07:32:44 pm
content: Hi,I'm making my first audio amplifier. It's rather simple because I'm just using two TDA2050 op-amps in a layout showed in the datasheet. I'm studying electric engineering and I have the means to build it but I don't know what kind of supply should I use. I would use it on a pair of 4Ohm 50W speakers. I don't want to get close to the 50W, I don't want it to be loud but I want it to be as clear as possible. I was thinking about using a switched mode supply because I would like to keep as packed as possible. I think around 35V of output voltage should be good but I don't know how many amps do the amplifiers draw.I've attached the schematic and the board in case anything should be changed in it.Every suggestion is much appreciated.

author: Rerouter
author_rank: Super Contributor
timestamp: March 24, 2012, 08:41:41 pm
content: from its datasheet, it wouuld appear to have an average loading of 1A per op amp with peak demand of 5A, so at 35V you would be driving close to an average of 35W, (because 1A average) with the odd peak up to about 170W, now that will only likely be for microseconds, but its good to make sure your supply or bulk capacitance can supply this when it does peak, and that any circuitry following your op amps can handle or suppress to the level you want on these peaks,

author: ciccio
author_rank: Frequent Contributor
timestamp: March 24, 2012, 09:44:33 pm
content: Please do not attach Eagle files, but print them to PDF and post the PDF.This makes easier for other member to see what we are talking about.I cannot see your schematic, but you can make some simple math:50W RMS on a 4 ohm load > 14.14 V RSM > 3.54 A RMS x 2 channels > 7.04 A RMS. DC voltage should be +/- 22.5 V DC.When designing the PSU, you must be sure that the voltage will not exceed the amplifier's maximum rating even when mains voltage is 10% higher than nominal, so you must decrease the nominal DC voltage by at least 10%.This means the power supply should be rated at + /- 20 V dc, 7 A, that is a lot of power, in the order of 280 W.Usually audio amplifiers power supplies are underrated, sometimes by 50 %, because maximum power will last for a very short time, with music signals, so the power supply may be allowed to "sag".See this very good article:http://sound.westhost.com/power-supplies.htm#supply-requirementsor this other :http://www.tnt-audio.com/clinica/ssps1_e.htmlWhy did you choose a TDA2050?From my experience, the LM3886 is better sounding, and less prone to failure...Regards

author: abzoli
author_rank: Newbie
timestamp: March 25, 2012, 02:35:19 pm
content: The only reason I'm using the TDA2050 is because It's easier to understand and to build.How can Rerouter say 170W is enough while you say 280W? That's a big difference.Are the schematics in the link just examples and need more components for real usage or actual designs and can be used?

author: Rerouter
author_rank: Super Contributor
timestamp: March 25, 2012, 07:26:42 pm
content: i was working off the datasheet for the op amps, while ciccio was working off the loading of a 4 ohm speaker,http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1461.pdffigure 7,it shows for a 35V supply (17.5 because of single supply) your mean power will be around 35W or 1A, even if the math behind it eludes me,

author: ciccio
author_rank: Frequent Contributor
timestamp: March 26, 2012, 10:57:56 am
content: Quote from: abzoli on March 25, 2012, 02:35:19 pmI used a lot (thousands) of LM3886, without problems, so I'm a little biased toward it, and don't know well the TDA 2050 (I tested it only once, years ago).I agree with Rerouter:If you want continuous power (what is "incorrectly" called RMS power) my calculations are correct (I hope so..). The TNT audio article gives similar results.If you want "dynamic" power (what is sometimes called "music" power) your power supply may be of lower specs, and usually you end up with an amplifier that is very similar in dynamic response to the one with a bigger power supply, but that will have problems in reproducing loud low frequencies passages.Please have a look at the powered speakers that are sold for computer use: only an handful of manufacturers (only Creative, for what I remember), specifies continuous power for their products: all the other label them in terms of "PMPO" power (I cannot decipher this acronym) that says that you can have 15 +15 W "PMPO" from an amplifier whose power transformer is clearly labeled as a 8n VA unit.That's more than free energy or perpetual motion...Best regards

author: T4P
author_rank: Super Contributor
timestamp: March 26, 2012, 02:24:32 pm
content: PMPO is peak momentary power outputIt's rated at being able to last 1ns .It's all a big fat lie .Thankfully big proper companies do not put PMPO ratings neither do any of the coporations now days .Like logitech , creative , corsair and the like .