Post by thread:[EE] : Influence of the coil in Boost Switching Re

>I'm currently designing a Boost regulator to convert 12V to 14V. I plan to >use the LM2587 from NS. This reg needs a coil but I can find nowhere the >influence of this coil. I assume you probably mean the LM2578 rather than ...87??? The coil is absolutely vital to the design. I suggest you search for switching regulator design articles on the web. HThere are many but here is a good one that covers what you need to know http://www.smpstech.com/tutorial/t02top.htm Here is a very simple "what" without much "why". In a boost regulator there are two stages to the regulation phase. In stage 1 the coil input connects to Vin and the coil output is grounded. Current fow in the coil increases until some preset limit is rached or until a certain time has passed. In stage two the connection to ground is removed. The current MUST continue to flow without interuption and the coil polarity reverses so the end which causes the end which was grounded to now be above Vin and this end is connected to Vout by a diode to provide output power. The cycle then repeats. >Can anybody help me to choose this coil (specially the value). I need 5A >output capability. > >Input : 12V/7Ah (Pb Accumulator), Output 13.8V /50W >and next 12V/4Ah (NiCd Accumulators), output 13.8V/50W The national "Simple Switcher" application notes contain suggested inductor suppliers.. Without going into design detail at all, you will probably want a coil with an inductance in the range of 50 to 300 uH depending on various design constraints. As a guide this will probably be a powdered iron core in the 10 to 20mm outer diameter range with tens of turns on it. The LM2578 datasheet provides inductor design calculations. For this level of current you will need to use an external switch. Consider also using a more modern IC eg a UCC3803 or UCC3805 (improved versions of a very old design) which has some advantages due to implementing current mode control. The latter is slightly easier for a beginner to design with. The data sheets and applications notes provide most of what you want to know for designs using these. http://www.unitrode.com (now part of TI) Search for app note U-133, SLUS270A, & others Russell McMahon _____________________________ What can one man* do? Donate food daily free !!! - http://www.thehungersite.com/ Donate Vitamin A! http://www.thechildsurvivalsite.com/ http://www.rawa.com - one perspective on Afghanistan http://www.changingourworld.com http://www.easttimor.com http://www.sudan.com (* - or woman, child or internet enabled intelligent entity :-)) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Thanks for the links. There was no error on the part, the reference of th switching regulator is LM2587, it's a 5A Flyback regulator - simple boost regulator {Quote hidden}> -----Message d'origine----- > De: Russell McMahon [SMTP:spam_OUTapptechTakeThisOuTCLEAR.NET.NZ] > Date: mercredi 24 janvier 2001 13:16 > À: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Objet: Re: [EE] : Influence of the coil in Boost Switching > Regulators > > >I'm currently designing a Boost regulator to convert 12V to 14V. I plan > to > >use the LM2587 from NS. This reg needs a coil but I can find nowhere the > >influence of this coil. > > > I assume you probably mean the LM2578 rather than ...87??? > > The coil is absolutely vital to the design. > I suggest you search for switching regulator design articles on the web. > HThere are many but here is a good one that covers what you need to know > > http://www.smpstech.com/tutorial/t02top.htm > > Here is a very simple "what" without much "why". > > In a boost regulator there are two stages to the regulation phase. > > In stage 1 the coil input connects to Vin and the coil output is grounded. > Current fow in the coil increases until some preset limit is rached or > until > a certain time has passed. > > In stage two the connection to ground is removed. The current MUST > continue > to flow without interuption and the coil polarity reverses so the end > which > causes the end which was grounded to now be above Vin and this end is > connected to Vout by a diode to provide output power. > > The cycle then repeats. > > >Can anybody help me to choose this coil (specially the value). I need 5A > >output capability. > > > >Input : 12V/7Ah (Pb Accumulator), Output 13.8V /50W > >and next 12V/4Ah (NiCd Accumulators), output 13.8V/50W > > > The national "Simple Switcher" application notes contain suggested > inductor > suppliers.. > Without going into design detail at all, you will probably want a coil > with > an inductance in the range of 50 to 300 uH depending on various design > constraints. > As a guide this will probably be a powdered iron core in the 10 to 20mm > outer diameter range with tens of turns on it. > > The LM2578 datasheet provides inductor design calculations. > > For this level of current you will need to use an external switch. > Consider also using a more modern IC eg a UCC3803 or UCC3805 (improved > versions of a very old design) which has some advantages due to > implementing > current mode control. The latter is slightly easier for a beginner to > design > with. The data sheets and applications notes provide most of what you want > to know for designs using these. > > http://www.unitrode.com (now part of TI) > > Search for app note U-133, SLUS270A, & others > > > > Russell McMahon > _____________________________ > > What can one man* do? > Donate food daily free !!! - http://www.thehungersite.com/ > Donate Vitamin A! http://www.thechildsurvivalsite.com/ > http://www.rawa.com - one perspective on Afghanistan > http://www.changingourworld.com http://www.easttimor.com http://www.sudan.com > > (* - or woman, child or internet enabled intelligent entity :-)) > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.