Getting started with Switcher design
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From: C Egernet on 3 Aug 2010 11:23 I've seen switching power supplies mentioned occasionally here. I'd like to learn about designing such power supplies: choice of controller chips, MOSFETs and inductors. I know about the principle of buck and boost but that is about it. Where should I start? There must be a good app note to get going. (I realize that not all app notes are created equal, thus the question.) A first project could be a 12V (a couple of amps) power supply for a communications receiver I've put together. Is a flyback topology feasible? Chris
From: Michael Black on 3 Aug 2010 13:23 On Tue, 3 Aug 2010, C Egernet wrote: > I've seen switching power supplies mentioned occasionally here. > > I'd like to learn about designing such power supplies: choice of > controller chips, MOSFETs and inductors. I know about the principle of > buck and boost but that is about it. > > Where should I start? There must be a good app note to get going. (I > realize that not all app notes are created equal, thus the question.) > > A first project could be a 12V (a couple of amps) power supply for a > communications receiver I've put together. Is a flyback topology > feasible? > Why would you want to do that? A receiver isn't going to draw much current, yet to use a switching supply means you have to deal with all the noise that such supplies generate, not a good thing when building a receiver. The effort in making the power supply as noise free as possible might be a useful learning process, if there was an actual need for higher current, but it's not. As for the rest, define what you want to do. Do away with transformers? Provide regulation without a lot of loss? The best place to start would seem to be a hybrid, start with a 60Hz stepdown transformer, rectifiers and a filter capacitor, and then build a switching regulator. Learn from that, don't get lost in extra stages, and then later you can go to a full switching supply. Michael
From: Tim Wescott on 3 Aug 2010 13:40 On 08/03/2010 10:23 AM, Michael Black wrote: > On Tue, 3 Aug 2010, C Egernet wrote: > >> I've seen switching power supplies mentioned occasionally here. >> >> I'd like to learn about designing such power supplies: choice of >> controller chips, MOSFETs and inductors. I know about the principle of >> buck and boost but that is about it. >> >> Where should I start? There must be a good app note to get going. (I >> realize that not all app notes are created equal, thus the question.) >> >> A first project could be a 12V (a couple of amps) power supply for a >> communications receiver I've put together. Is a flyback topology >> feasible? >> > Why would you want to do that? A receiver isn't going to draw much > current, yet to use a switching supply means you have to deal with > all the noise that such supplies generate, not a good thing when > building a receiver. Perhaps for his stated purpose -- to learn? Building quiet switchers used to be real voodoo, but there's a lot of interest in them and hence a lot of knowledge floating around out there. The biggest "trick" that I'm aware of is controlled slew rates on the gate drives, to slow down the edges on the FET outputs. You trade switching loss for EMI, which is a nice way to guarantee employment. > The effort in making the power supply as noise free as possible might > be a useful learning process, if there was an actual need for higher > current, but it's not. Your "low current" may be my "high current", though. > As for the rest, define what you want to do. Do away with transformers? > Provide regulation without a lot of loss? > > The best place to start would seem to be a hybrid, start with a 60Hz > stepdown transformer, rectifiers and a filter capacitor, and then build > a switching regulator. Learn from that, don't get lost in extra stages, > and then later you can go to a full switching supply. Amen. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Tim Wescott on 3 Aug 2010 13:42 On 08/03/2010 08:23 AM, C Egernet wrote: > I've seen switching power supplies mentioned occasionally here. > > I'd like to learn about designing such power supplies: choice of > controller chips, MOSFETs and inductors. I know about the principle of > buck and boost but that is about it. > > Where should I start? There must be a good app note to get going. (I > realize that not all app notes are created equal, thus the question.) > > A first project could be a 12V (a couple of amps) power supply for a > communications receiver I've put together. Is a flyback topology > feasible? From what power source? The wall? A battery? What voltage battery? What constraints do you want to place on yourself? What don't you care about? If you're going to go off the wall, search on "off-line switchers" for information. AFAIK flyback topologies are generally most useful when you're going up in voltage. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Hammy on 3 Aug 2010 18:41
On Tue, 03 Aug 2010 10:42:24 -0700, Tim Wescott <tim(a)seemywebsite.com> wrote: >On 08/03/2010 08:23 AM, C Egernet wrote: >> I've seen switching power supplies mentioned occasionally here. >> >> I'd like to learn about designing such power supplies: choice of >> controller chips, MOSFETs and inductors. I know about the principle of >> buck and boost but that is about it. >> >> Where should I start? There must be a good app note to get going. (I >> realize that not all app notes are created equal, thus the question.) >> >> A first project could be a 12V (a couple of amps) power supply for a >> communications receiver I've put together. Is a flyback topology >> feasible? > > From what power source? The wall? A battery? What voltage battery? >What constraints do you want to place on yourself? What don't you care >about? > >If you're going to go off the wall, search on "off-line switchers" for >information. > >AFAIK flyback topologies are generally most useful when you're going up >in voltage. A flyback is useful for more then just boosting voltages. Its simple to derive multiple output voltages either negative or positive polarity. It provides galvanic isolation from the rectified line voltage.Its one of the least complex lowest part counts converters for offline power conversion. Almost every consumer and or industrial electronic device under a 100W is getting its power from a flyback converter. The OP should go and browse ONsemis and Fairchilds site for offline controllers for tons of info includeing examples and sources for small quantity magnetic's. I don't know why you would use anything other then a flyback for 100W or less for a line powered converter when primary to secondary isolation is a must. They are even the prefered topology for TELCO power conversions all kinds of examples for 48Vdc conversion useing a flyback are avaliable on google. |