Dual polarity supply -- no center tap
in [Design]
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From: mkr5000 on 30 Sep 2009 13:26 I'll be darn -- don't know why I haven't considered that before and for a power amp you don't want a regulated supply. Is the added ripple a problem? Or do the caps near the chip take care of it?
From: Rich the Cynic on 30 Sep 2009 14:09 On Wed, 30 Sep 2009 10:26:16 -0700, mkr5000 wrote: > I'll be darn -- don't know why I haven't considered that before and > for > a power amp you don't want a regulated supply. Well, technically, you might _want_ a regulated supply, depending on your style. But you don't _need_ them if your amp has good enough power-supply immunity. > Is the added ripple a problem? > Or do the caps near the chip take care of it? Ripple can be a problem if the amp doesn't have good supply immunity; the filter caps are supposed to filter the ripple. There's some formula for calculating their values for x amount of ripple, but I just put in the biggest (i.e., most capacitance) caps that will fit. (and that I can afford. ;-) ) Have Fun! Rich
From: Phil Hobbs on 30 Sep 2009 14:15 George Herold wrote: > On Sep 30, 12:03 pm, Phil Hobbs > <pcdhSpamMeSensel...(a)electrooptical.net> wrote: >> mkr5000 wrote: >>> I've never used a "voltage inverter" -- I see that Maxim makes a chip >>> that will convert +5v to -5v and I would imagine >>> they can be used in a dual polarity supply. >>> However, I want to build an audio power amp supply for an LM3886 -- >>> wonder if there's a chip or circuit that will >>> do the same thing at higher voltages (+ and - 30v -- even higher >>> maybe). >>> Always used a center tap transformer for this but was wondering about >>> the creative use of a single secondary >>> transformer. >>> Or should I stick to the conventional dual winding approach? (I do >>> hate potential problems). >>> Thanks. >> How about a full-wave voltage doubler? Ground one end of the secondary, >> connect A of one diode and K of the other to the other end. Makes two >> half-wave rectifiers of opposite polarity, total voltage ~2.5 to 2.8 x >> VRMS. >> >> Cheers >> >> Phil Hobbs >> >> -- >> Dr Philip C D Hobbs >> Principal >> ElectroOptical Innovations >> 55 Orchard Rd >> Briarcliff Manor NY 10510 >> 845-480-2058 >> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text - >> >> - Show quoted text - > > Phil are you sure you get the doubling effect AND two polarities? > > you mean a circuit like this, > http://www.play-hookey.com/ac_theory/ps_v_multipliers.html > > But most likely I just misunderstood. > > George H. > The OP was talking about a bipolar supply based on a centre tapped transformer and bridge rectifier, I thought, and wondering if it were possible to get +- voltage without it. A full wave doubler (or equivalently two half wave rectifiers) gets you a bipolar supply with one winding. You still get the doubled voltage difference, the only difference is what you call ground. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: Jan Panteltje on 30 Sep 2009 14:15 On a sunny day (Wed, 30 Sep 2009 10:26:16 -0700 (PDT)) it happened mkr5000 <mikerbgr(a)gmail.com> wrote in <6710fdbd-7150-4c96-a548-6f0477a43177(a)g19g2000yqo.googlegroups.com>: >I'll be darn -- don't know why I haven't considered that before and >for >a power amp you don't want a regulated supply. > >Is the added ripple a problem? No problem, that chip has good supply rejection, typical 70 dB.
From: Rich Grise on 30 Sep 2009 14:13
On Wed, 30 Sep 2009 09:46:41 -0700, George Herold wrote: > On Sep 30, 12:03�pm, Phil Hobbs > <pcdhSpamMeSensel...(a)electrooptical.net> wrote: >> mkr5000 wrote: >> > I've never used a "voltage inverter" -- I see that Maxim makes a chip >> > that will convert +5v to -5v and I would imagine >> > they can be used in a dual polarity supply. >> >> > However, I want to build an audio power amp supply for an LM3886 -- >> > wonder if there's a chip or circuit that will >> > do the same thing at higher voltages �(+ and - 30v �-- even higher >> > maybe). >> >> > Always used a center tap transformer for this but was wondering about >> > the creative use of a single secondary >> > transformer. >> >> > Or should I stick to the conventional dual winding approach? �(I do >> > hate potential problems). >> >> How about a full-wave voltage doubler? �Ground one end of the secondary, >> connect A of one diode and K of the other to the other end. �Makes two >> half-wave rectifiers of opposite polarity, total voltage ~2.5 to 2.8 x >> VRMS. > > Phil are you sure you get the doubling effect AND two polarities? > > you mean a circuit like this, > http://www.play-hookey.com/ac_theory/ps_v_multipliers.html > > But most likely I just misunderstood. After looking at that circuit, do you still misunderstand? The _total_ voltage is 2.8 * Vpk, but that's split between the two supplies. And it's only two half-wave rectifiers, back-to-back, so your ripple per current will be way more than a full-wave. (I'd have to look up the numbers, but I'll leave that as an exercise for the student. ;-) ) Cheers! Rich |