Ok, sorry for misunderstanding the part with offline reply, that's because english is not my mother tongue :) Russell, I don't need to hide, and I already stated the problem with the power supply I want to build in another post, and I got some answers that were useful for me, but when I saw your regulator, I thought it could be used in my circuit also, reducing the costs of the power supply. The input voltage would be between 14 and 22.4V, from a 16V transformer, with a rectifier bridge and an 4700uF filter capacitor. Could the voltage be applied directly to the schematic you provided ? Is it necessary another filter capacitor ? I still need to calculate the ripple at 3A and see if I can find a capacitor with so much ripple. 80% efficiency is good, and I can bear with it, I don't need to obtain 99% out of it. The output is to be 13.8V, and I don't know exactly which resistors I would have to change for that. For 3A, I know I would have to use a FET which resists at this load, I don't know exactly the amount of power to be dissipated, and which would be the part to dissipate more heat - the FET ? Tha application is a security system, and the load of 3A maximum would be when the bell goes on - very rarely, and for a short time. The load is composed of the sensors, the bell, other devices at around 12V and a regulator at 5V for the other circuitry (not power consuming). I hope there aren't too many questions to annoy you... Thank you very much for your help. Lucian ----- Original Message ----- From: "Russell McMahon" To: "PIC List" Sent: Tuesday, December 21, 2004 11:26 AM Subject: Re: [EE] Low cost switching regulators > Got this response offlist - probably thought my offlist request re religious > stuff related to technical matters as well. > I told them I would respond on list but not identify them. They can self > identify if they wish,. > > > _____________________ > > Hello, > > I am very interested of one of those regulators, for a power supply I want > to build, where the cost is most important, and after that the efficiency. > Around which value is the efficiency though ? I guess that's more than a > linear power supply... > > I am beginner with electronics, so I have a limited capacity to understand > your circuit. I want to build a 13.8V power supply, that would be capable of > giving at maximum 3A of current. Could you indicate me the key parts that > need to be changed for that job ? And in the schematic, there is the > complete circuit ? Or just a part of it ? > > Thank you for answering ! > > _______________________________________________ > > That is more or less the whole circuit - although there are always bits and > pieces that need adding on in a real circuit. > A filter capacitor on Vin is a very good idea. Depending on what the load > is it MAY be a good idea to add a small output resistor in series with the > output with a larger filter capacitor to ground after it. > > You don't say whether 13.8v is input or output. > What are your desired input and output voltages? > What is the circuit to be used for? > The more you can tell about your application the easier it is to give good > answers. > > Why is the cost important? - are you wanting to build many or just a few or > one? If a few or one then you MAY find that a commercial circuit or an IC is > still an OK solution. > > The efficiency can probably reach 80%+ depending on many factors. I suspect > it would never get to 90%+. My friend who is using it to give 12v from 20v > to 35v in is getting 70%+. > > For a 3A design using a FET may be a good idea. A P channel FET is needed - > which one depends on the required Vin . > > NOTE - while this circuit COULD be used from rectified mains to 13.8 volts > DC I would not recommend doing so! The output is not isolated and the > circuit is "unusual" enough that you would want to have lots of confidence > that the design worked under all conditions. Mains can be very tricky. > > Tell us more and see how it goes. If you don't want the list to know who you > are you can ask me offlist and I'll answer on list. For technical things > like this it's a very good idea to ask onlist so all can share with you. > > What I said at the start about answering me offlist only applied to anything > applying to how God related to the design - some people get extremely > annoyed when such things are discussed onlist. > > > > Russell McMahon > > > > > > -- > No virus found in this outgoing message. > Checked by AVG Anti-Virus. > Version: 7.0.296 / Virus Database: 265.6.2 - Release Date: 20/12/2004 > > _______________________________________________ > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > _______________________________________________ http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist