09-01-06, 02:20 AM
Before I go off and buy all the parts and try to build suitable pcbs thought I'd see if anyone has any knocking about they'd be prepared to sell? I'm after 4 pcbs probably, though 2 would do as a starter.
Also open to suggestions on alternative +ve/-ve regs? input will be +-14v - need to get it under +-13v to run my 8620 opamps under their max stress levels.
ps, if anyone has a list of R values and most suitable caps (not oscons I gather for the output...) would be greatly appreciated
I don't have any boards, but have a few LM317T regs you're welcome to. Not new, but in perfect condition. As for caps, tants are recommended in the datasheet which you can view here: http://www.national.com/ds.cgi/LM/LM117.pdf (ignore the fact it's for the LM117, it's also the sheet for the 317).
The formula for calculating the correct resistor values are also in the datasheet.
Edit: alternatively, you could take the easy option and use L7812CV and L7912VC regulators (+ and - versions, respectively). They're probably a bit more noisy, but will give you a fixed 12v output without the hassle of figuring out resistors, etc.
If price/time wasn't an option, I'd go the whole hog and build some of Andy's super regs - the 317 / 7x12 regs can't even come close to that kind of performance.
Hope that helps.
09-01-06, 03:50 AM
thanks for the input Carl. Price is a restraint at the moment, plus there's no regulation at the moment so I want to see what effect a cheap 317/337 setup gives me to start with. I may investigate the fixed regs you mention - is a 14v input enough headroom to get the 12v out?
The L7812 and L7912 series require at least 2v headroom, but the datasheet does state that they may sometimes require 2.5v... I'm no guru here so don't know what to advise, but for a few pennies (you can get them for under a quid at Maplin: http://www.maplin.co.uk/Module.aspx?ModuleNo=7937&&source=14&doy=9m1) it's worth a bash!