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From: John Fields on 14 Aug 2006 13:50 On 13 Aug 2006 06:03:46 -0700, meow2222(a)care2.com wrote: >To get +-50v dc you need the same transformer, no reason to have 2 >windings at all. So you just need one 50v winding. --- I don't think that's true. (View in Courier) Consider a conventional full wave bridge: +----+---------+ | | | MAINS>----+ | [CR1] [CR3] | | |A |K P||S +--[C1+]--+--->V+ R||E | | I||C +---------|--->V- | | |A |K MAINS>----+ | [CR2] [CR4] | | | +----+---------+ Note that (neglecting the secondary IR losses) for a 50VRMS secondary winding the voltage from V+ to V- will be: VDC = (VRMS * sqrt(2)) - (2Vf) = (50 * 1.414) - 1.5V ~ 69.2V Since either V+ or V- could be used as a [ground] reference, then the output of the supply could be either +62.5V or -62.5V, but not + and - at the same time. An artificial reference could be constructed so that the output of the supply would be symmetrical and "simultaneously bipolar", but in that case the output would be +/- 34.6VDC, not +/- 50VDC. In order to get simultaneous + and - outputs what's usually done (if separate transformers aren't used), is this: +--[CR2>]--+--->V+ | | +--[CR1>]--+ | |+ MAINS>----+ | [C1] P||S | R||E----------+--->GND I||C |+ | | [C2] MAINS>----+ | | +--[<CR3]--+ | | +--[<CR4]--+--->V- Now, if we have a single 50V winding it'll have to be center-tapped, with the result that there'll be 25V RMS on either side of the secondary, and the DC output will be: VDC = (VRMS * sqrt(2)) - (Vf) = (25 * 1.414) - .75 ~ 34.6V For the negative side the result will be the same, but the sign will be different. So, we still didn't get +/- 50VDC from a transformer with a single 50V winding. -- John Fields Professional Circuit Designer
From: John Woodgate on 14 Aug 2006 13:47 In message <p391e293rqbghr5837mqonr7p7ds2ogcuf(a)4ax.com>, dated Mon, 14 Aug 2006, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> writes >See.... > >http://analog-innovations.com/SED/2N1358.jpg I discovered, to my surprise, that you can still get ADZ12s, although they are EUR 32 each. The fbeta of these is measured in inverse minutes. (;-) -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk 2006 is YMMVI- Your mileage may vary immensely. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
From: meow2222 on 14 Aug 2006 14:17 John Fields wrote: > On 13 Aug 2006 06:03:46 -0700, meow2222(a)care2.com wrote: > > > >To get +-50v dc you need the same transformer, no reason to have 2 > >windings at all. So you just need one 50v winding. > > --- > I don't think that's true. (View in Courier) Youre not the only person to say this, and I find it very puzzling, as the means to get +/- 50v is elementary: +-----|<|------- V- MAINS>----+ | | +-----|>|------- V+ P||S R||E I||C | | MAINS>----+ | | +--------------- 0V NT
From: John Fields on 14 Aug 2006 14:25 On Mon, 14 Aug 2006 12:50:16 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On 13 Aug 2006 06:03:46 -0700, meow2222(a)care2.com wrote: > > >>To get +-50v dc you need the same transformer, no reason to have 2 >>windings at all. So you just need one 50v winding. > >--- >I don't think that's true. (View in Courier) > > >Consider a conventional full wave bridge: > > +----+---------+ > | | | >MAINS>----+ | [CR1] [CR3] > | | |A |K > P||S +--[C1+]--+--->V+ > R||E | | > I||C +---------|--->V- > | | |A |K >MAINS>----+ | [CR2] [CR4] > | | | > +----+---------+ > >Note that (neglecting the secondary IR losses) for a 50VRMS >secondary winding the voltage from V+ to V- will be: > > > VDC = (VRMS * sqrt(2)) - (2Vf) = (50 * 1.414) - 1.5V ~ 69.2V > > >Since either V+ or V- could be used as a [ground] reference, then >the output of the supply could be either +62.5V or -62.5V, but not + >and - at the same time. An artificial reference could be >constructed so that the output of the supply would be symmetrical >and "simultaneously bipolar", but in that case the output would be >+/- 34.6VDC, not +/- 50VDC. > >In order to get simultaneous + and - outputs what's usually done (if >separate transformers aren't used), is this: > > +--[CR2>]--+--->V+ > | | > +--[CR1>]--+ > | |+ >MAINS>----+ | [C1] > P||S | > R||E----------+--->GND > I||C |+ > | | [C2] >MAINS>----+ | | > +--[<CR3]--+ > | | > +--[<CR4]--+--->V- --- Aarghhhh!!! Big OOPS... +-----[CR1>]--+--->V+ | | | +--[CR2>]--+ | | | MAINS>----+ +------+ | |+ | | | | [C1] P||S | | | R||E------|--|----------+--->GND I||C | | |+ | | | | [C2] MAINS>----+ +------|--+ | | | | | +--[<CR3]--+ | | +-----[<CR4]--+--->V- -- John Fields Professional Circuit Designer
From: John Fields on 14 Aug 2006 14:59
On 14 Aug 2006 11:17:33 -0700, meow2222(a)care2.com wrote: >John Fields wrote: >> On 13 Aug 2006 06:03:46 -0700, meow2222(a)care2.com wrote: >> >> >> >To get +-50v dc you need the same transformer, no reason to have 2 >> >windings at all. So you just need one 50v winding. >> >> --- >> I don't think that's true. (View in Courier) > >Youre not the only person to say this, and I find it very puzzling, as >the means to get +/- 50v is elementary: > > +-----|<|------- V- >MAINS>----+ | > | +-----|>|------- V+ > P||S > R||E > I||C > | | >MAINS>----+ | > | > +--------------- 0V --- Well, I can't argue with that, LOL, but by doing it that way you've just made the smoothing caps twice as big as they have to be since you've halved the frequency of the rectified AC. Also, you've increased the current the diodes _and_ the transformer need to handle. -- John Fields Professional Circuit Designer |