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 small smps with uc3844
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 26th November 2005, 09:30 PM #1 Banned   Join Date: Jan 2005 small smps with uc3844 Hello! Is it possible to make a little bipolar 35v smps capable of delivering about 2.5A, that runs on 12vdc with a UC3844, four paralelled 2SC2625 transistors and some other components required around the transformer ? The transformer i'll wind myself, is the winding ratio the same for a flyback type smps as for a pushpull one ? How big does the core need to be to make a 100-150w smps ? I have this idea to use it with the 1982 elektor amp.
 26th November 2005, 11:21 PM #2 Banned   Join Date: Jan 2005 TL494 EDIT: UC3844 needed 16v to start so lets go with TL494 instead. Is this possible ? How thick wire do i need to use to get 35v 2.5A out ?
 28th November 2005, 06:19 AM #3 diyAudio Member   Join Date: Jun 2005 Location: IASI
 28th November 2005, 09:43 AM #4 Banned   Join Date: Jan 2005 Nice page But it only calculates one output winding, i need two as a amp needs bipolar power supply.
 28th November 2005, 12:56 PM #5 diyAudio Member   Join Date: Jun 2005 Location: IASI You can take into account the total output power and efficiency. For example if you want +35V/2.5A and -35V/2.5A, then your output power is Pout = 175W. In order to use the program, you can set, for example, the output voltage equal to 35V and for output current use Iout = Pout/(Vout*efficiency) With this settings, program will return a value for the primary current which is close to reality. The value for primary wire diameter could be used. For secondary windings, you have to set Iout = 2.5A and the program will do the rest. The specified value for secondary wire diameter is a good choice. Have fun !
 28th November 2005, 03:43 PM #6 Banned   Join Date: Jan 2005 Something like this ?
 28th November 2005, 04:38 PM #7 diyAudio Member     Join Date: Dec 2003 Location: Nottingham UK Use a 3843 for 12V boost operation. It has a lower startup/shutdown threshold.
 28th November 2005, 04:42 PM #8 diyAudio Member     Join Date: Dec 2003 Location: Nottingham UK At the sort of output power you're asking for, you'll probably need to run your flyback supply in continuous-conduction mode, so make sure your feedback stabilisation is happy with operation in both discontinuous and continuous mode. (The app notes for a TL3843, UC3843 etc will explain this). Don't use a TL494, horrible old things! TL3843s cost pennies.
 28th November 2005, 05:39 PM #9 diyAudio Member   Join Date: Jul 2005 Location: 65N 25E 2SC2625 is mediocre when switching 20amps at 12v. Try some mosfets.
 28th November 2005, 09:44 PM #10 Banned   Join Date: Jan 2005 First prototype running Now i have built a first prototype around a UC3844, two IRFI640 and a transformer made with a emi filter toroid. The thing gives out around 20.2 volts and can actually drive the elektor amp, tho the voltage is alittle too low but i have tried to turn the bass up with no prob, i took it quite loud and voltage only drivved to 19v, pretty impressive for a first prototype built around a emi filter toroid. Heres some pics: A little video: smps and amp running

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