Hello Folks,
Got to make roughly 220VDC on a new board where I'll have a 12VDC rail. Not a big deal, or so I thought until I looked at the smorgasboard of ferrite transformers. All the (available) CCFL transformers with the lowest turns ratio are 50 or higher, like this series:
Of course I'd need a little less than 40. Are there any in that range?
If not I'd have to regulate the thing. Again. Dang. I don't want to but man's got to do what man's got to do.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
How much current do you need? How well regulated?
A flyback, with a single inductor, or a center-tapped inductor, might work, using standard parts.
Do you have another of those every-penny-counts situations?
John
20mA maybe. I'll follow it with a linear regulator.
Yeah, if Digikey has tapped inductors with gapped (or non-closed) cores that would work. Thanks for the hint, I'll take a look. Although I must be careful not to spew too much electromagnetic stuff around in there.
No, this one isn't super critical. If there was a COTS module small enough to do this I'd bite.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
I'm not at all sure what the details are for that part. Is the ratio for half the primary to the secondary, or the whole primary to the secondary? What is the turns ratio for the feedback winding?
Can you use both the full primary and the feedback winding is series as a primary to drive with a 12 volt bridge?
Must the 220 volt output be isolated from the 12 volt supply?
-- Regards, John Popelish
50:1 with a center-tap supplied by 12V, driven push-pull (~1V switch drop) will give about 225V output, when full-wave rectified.
RL
Aiee...
Topological dyslexia? 50:1 capacitively coupled to a a half-bridge reduces the effective input voltage for the non-optimal turns ratio, with the ~volt switch loss, produces about 250V. Perhaps the feedback winding, wired in series with the primary, can cut this down some more.
RL
Take a look for the Photoflash-transformer-supplier. (Würth etc) Ususallly the output for their transformers ist something around
350V....hth
- Michael Wieser
I don't know. The specs for those things are very skimpy and such "minor" details are left off.
That is a good idea. The only way to find out would be to measure one. Unless I see anotehr solution I'll just order a few with the next Digikey round.
No, same ground.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Hmm, on the HP11C it comes to 275V.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Does anyone know the typical turns percentage of a CCFL feedback winding WRT the primary?
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
They are hard to find in the US. But thanks, I'll take a look.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
P.S.: It's for the whole primary.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Würth aquired Midcom... an other supplier:
- Michael Wieser
I just wish they'd introduce their stuff at Digikey etc. This is more important in the marketplace than many companies assume, especially EU companies need to realize that.
Thanks. Looks like the highest ratio is the one for photoflash at 15:1. But it's not a mainstream series, for example their flybacks are not available at Digikey.
I'll probably just take a Miller PM61300 CCFL transformer (which Digikey has) and regulate.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Also usually gapped designs, because they are operated=20 flyback, into the effective short circuit of a large, slowly=20 charging capacitor most of their operation time.
--=20 Regards,
John Popelish
(snip)
Thanks. I guess I should buy one to see what the typical primary to feedback ratio is. The data sheet looks like something made after a custom design was reluctantly released for other buyers, not like something designed by the maker and fully speced to drum up sales.
-- Regards, John Popelish
-- Mark
Yup, sure looks like that. I am dealing with lots of those kinds of datasheets right now because I am doing a few HV circuits.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Thanks, but it looks like they don't have the poifect turns ratio either. And yes, last time I checked pricing I almost fainted.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
If it is for a very large quantity you could have some made. If it is one time or a very small series what is wrong with putting
212 turns on a pot core? Have done so many that way...ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.