Are there any 24VAC to 3.3VDC/1.5A SMPS?
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From: Joerg on 5 Jun 2010 11:37 Spehro Pefhany wrote: > On Fri, 04 Jun 2010 17:56:04 -0700, the renowned Joerg > <invalid(a)invalid.invalid> wrote: > >> Gents, >> >> Does anyone know of a little AC/DC switch mode converter module that can >> take 24VAC and put out well regulated 3.3V at 1.5A or more? $25 in 1k >> qty would be nice, availability in the US would be even nicer. >> >> All I see is 24VAC to 12VDC and placing two in a row costs effiency. >> Sure, I could roll my own again but this time we want to avoid NRE and >> agency hassle (EMC et cetera). > > 24VAC is not a very common voltage (24VDC is much more popular in > industrial applications). > It used to be very popular in Europe but I haven't seen any industrial switch gear there in some 15 years. All the power contactors for huge motors and such were run on 24VAC. Up to 30-50A. Larger ones still had 24VAC "control contactors" but they'd drive huge 230VAC contactors, the kind that sounds like a gunshot when they engage. While studying for my masters I assembled gear like that because those jobs paid quite well, compared to bussing tables :-) I still have a discarded supply transformer for a cabinet that was sold to me at scrap metal price. 24V, one kilowatt (!). That was from an older cabinet two stories high where you needed a ladder to get to some of the contactors. The secondary of that transformer consists of soaked-cloth insulated copper bar that was formed around the primary using a wooden mallet. > I second the suggestion of adding a bridge and filter cap upstream of > a converter, along with maybe a CM choke and some film or ceramic > caps. > Looks like I hafta :-( That's why I posted, was hoping for a silver bullet that lets me avoid it. > You didn't specify whether you needed isolated or not, that's going to > make a difference. > Yes, sorry, should be isolated but we could make it work without. AC/DC converters are generally isolated though because they use bridge rectifiers. > When you read the detailed app notes, most of the modules require some > filtering ahead of them to meet EMC requrements anyway (small caps and > CM choke maybe), so it's not really "extra" work. > Yes, and we'd put one on there anyhow because it affords some surge protection. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: whit3rd on 5 Jun 2010 13:03 On Jun 5, 8:24 am, Joerg <inva...(a)invalid.invalid> wrote: > Hammy wrote: [ 24VAC input, 3.3V 1.5A output required] > > You could just add a bridge rectifier and a filter cap. This would > > widen your selection to several hundred of the SMPS's that have a max > > input to 36 or 75 Vin. ... > We could probably get one from CUI for under $15, offsets the cost for a > good 105C/5000h or similar electrolytic up front. Value wrong! If you only need 5 watts, the 33V filter cap ought to be about 200 uF, not 5000 uF. Or does '5000h' mean something other than the capacitance value?
From: Hammy on 5 Jun 2010 13:32 On Sat, 05 Jun 2010 08:24:40 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Hammy wrote: >> On Fri, 04 Jun 2010 17:56:04 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> Gents, >>> >>> Does anyone know of a little AC/DC switch mode converter module that can >>> take 24VAC and put out well regulated 3.3V at 1.5A or more? $25 in 1k >>> qty would be nice, availability in the US would be even nicer. >>> >>> All I see is 24VAC to 12VDC and placing two in a row costs effiency. >>> Sure, I could roll my own again but this time we want to avoid NRE and >>> agency hassle (EMC et cetera). >> >> You could just add a bridge rectifier and a filter cap. This would >> widen your selection to several hundred of the SMPS's that have a max >> input to 36 or 75 Vin. ... > > >That's what Ross suggested and it's a solution I had planned for, but >only in case there really is no other option. We responded simultaneously. I had my secretary proof read for grammar and spelling.This explains the minor discrepancy in time stamp She's a bit slow but I keep her around because she's a good lay.:) > >> ... Cheapest one I could find with a quick search is >> >> http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=445-3306-ND > > >We could probably get one from CUI for under $15, offsets the cost for a >good 105C/5000h or similar electrolytic up front. Yea good 105c caps are pricey particularliy for 250VDC or better. I just paid 7 bucks for two of these for a off line SMPS. http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=P11629-ND It's hard being a mad scientist on a budget.;>)
From: krw on 5 Jun 2010 13:40 On Sat, 5 Jun 2010 10:03:57 -0700 (PDT), whit3rd <whit3rd(a)gmail.com> wrote: >On Jun 5, 8:24�am, Joerg <inva...(a)invalid.invalid> wrote: >> Hammy wrote: > >[ 24VAC input, 3.3V 1.5A output required] > >> > You could just add a bridge rectifier and a filter cap. This would >> > widen your selection to several hundred of the SMPS's that have a max >> > input to 36 or 75 Vin. ... > >> We could probably get one from CUI for under $15, offsets the cost for a >> good 105C/5000h or similar electrolytic up front. > >Value wrong! If you only need 5 watts, the 33V filter cap ought to be >about 200 uF, not 5000 uF. Or does '5000h' mean something other >than the capacitance value? I assumed 5k hours (@105C), not 5000 henries. ;-)
From: Joerg on 5 Jun 2010 14:25 Hammy wrote: > On Sat, 05 Jun 2010 08:24:40 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Hammy wrote: >>> On Fri, 04 Jun 2010 17:56:04 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> Gents, >>>> >>>> Does anyone know of a little AC/DC switch mode converter module that can >>>> take 24VAC and put out well regulated 3.3V at 1.5A or more? $25 in 1k >>>> qty would be nice, availability in the US would be even nicer. >>>> >>>> All I see is 24VAC to 12VDC and placing two in a row costs effiency. >>>> Sure, I could roll my own again but this time we want to avoid NRE and >>>> agency hassle (EMC et cetera). >>> You could just add a bridge rectifier and a filter cap. This would >>> widen your selection to several hundred of the SMPS's that have a max >>> input to 36 or 75 Vin. ... >> >> That's what Ross suggested and it's a solution I had planned for, but >> only in case there really is no other option. > > We responded simultaneously. I had my secretary proof read for grammar > and spelling.This explains the minor discrepancy in time stamp She's a > bit slow but I keep her around because she's a good lay.:) > Now, now ... :-) >>> ... Cheapest one I could find with a quick search is >>> >>> http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=445-3306-ND >> >> We could probably get one from CUI for under $15, offsets the cost for a >> good 105C/5000h or similar electrolytic up front. > > Yea good 105c caps are pricey particularliy for 250VDC or better. I > just paid 7 bucks for two of these for a off line SMPS. > > http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=P11629-ND > That must be a SMPS in disguise :-) > It's hard being a mad scientist on a budget.;>) 500mOhm Rdson can get a bit toasty. But I only need a 63V cap. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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