Dual polarity supply -- no center tap
in [Design]
|
From: MooseFET on 1 Oct 2009 21:09 On Oct 1, 1:07 pm, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > David Eather wrote: > > George Herold wrote: > >> On Sep 30, 2:13 pm, Rich Grise <richgr...(a)example.net> wrote: > >>> 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- Hide quoted text - > > >>> - Show quoted text - > > >> Yup I understand now. I'd just never seen this configuration for a > >> power supply before. > > >> George H. > > > Watch current levels - this configuration is only good for up to 38% of > > the rated AC current . > > You're sure it isn't 37% or 39%? (It does sort of depend on the copper > losses, leakage inductance, core behaviour, and filter cap value, after > all.) Where do you get that number? > > You always suffer a bit from average vs RMS current in the transformer, > but remember you're using both half cycles, exactly like a bridge > rectifier. If you're quoting (|I_plus| + |I_minus|)/I_rms, I think it's > probably better than that, but if you're quoting just one of the two, I > think that's probably a bit optimistic. I use the rule that if it is full wave, you always need half again as many VA as you hope to get in Watts out. If it is half wave, you need about double that number. > > 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
From: George Herold on 1 Oct 2009 22:19 On Sep 30, 9:07 pm, MooseFET <kensm...(a)rahul.net> wrote: > On Sep 30, 8:55 am, mkr5000 <miker...(a)gmail.com> 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. > > Font check: > iiiii This should > mmmmm line up > > Two bridges like this will give you both polarities with 120Hz ripple > instead of the 60Hz you normally get from a double. > > ----------+-----!!------ > / \ / \ > / \ GND / \ > (-V)--+ >! +--+----+ >! +--- (+V) > \ / \ / > \ / \ / > ----------+----!!-------+ > > The down side is the extra capacitors it takes.- Hide quoted text - > > - Show quoted text - Cool, It's going to take me a bit to follow all the currents in that circuit. Are the >! ,in the center of each bridge, diodes from the DC voltages to ground? Does this have a name? (Just thought I might find a schematic on the web with more details.)
From: David Eather on 2 Oct 2009 00:10 Phil Hobbs wrote: > David Eather wrote: >> George Herold wrote: >>> On Sep 30, 2:13 pm, Rich Grise <richgr...(a)example.net> wrote: >>>> 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- Hide quoted text - >>>> >>>> - Show quoted text - >>> >>> Yup I understand now. I'd just never seen this configuration for a >>> power supply before. >>> >>> George H. >> >> Watch current levels - this configuration is only good for up to 38% >> of the rated AC current . > > You're sure it isn't 37% or 39%? (It does sort of depend on the copper > losses, leakage inductance, core behaviour, and filter cap value, after > all.) Where do you get that number? > > You always suffer a bit from average vs RMS current in the transformer, > but remember you're using both half cycles, exactly like a bridge > rectifier. If you're quoting (|I_plus| + |I_minus|)/I_rms, I think it's > probably better than that, but if you're quoting just one of the two, I > think that's probably a bit optimistic. > > Cheers > > Phil Hobbs > > The number came (to me) from a transformer manufacturer, but has also been quoted in the RS catalogue (print - I don't know about on-line) and the Altronics catalogue. Not definitive sources I grant you. I should have mentioned that it applied to a capacitor filtered power supply. Vmax = 2.82 x Vac(rms) and Imax = .38 x Iac(rms). However. seeing that my brain is stuffed (the reason I retired) there may be "some" error there - just checking a catalogue and it says .28 .
From: MooseFET on 2 Oct 2009 05:22 On Oct 1, 7:19 pm, George Herold <ggher...(a)gmail.com> wrote: > On Sep 30, 9:07 pm, MooseFET <kensm...(a)rahul.net> wrote: > > > > > On Sep 30, 8:55 am, mkr5000 <miker...(a)gmail.com> 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. > > > Font check: > > iiiii This should > > mmmmm line up > > > Two bridges like this will give you both polarities with 120Hz ripple > > instead of the 60Hz you normally get from a double. > > > ----------+-----!!------ > > / \ / \ > > / \ GND / \ > > (-V)--+ >! +--+----+ >! +--- (+V) > > \ / \ / > > \ / \ / > > ----------+----!!-------+ > > > The down side is the extra capacitors it takes.- Hide quoted text - > > > - Show quoted text - > > Cool, It's going to take me a bit to follow all the currents in that > circuit. > Are the >! ,in the center of each bridge, diodes from the DC > voltages to ground? The >! is just to show which way all the diodes in the bridge are pointing. The cathodes are all on the end more towards the right. > Does this have a name? (Just thought I might find a schematic on the > web with more details.) It is just another version of the voltage doubler.
From: JosephKK on 4 Oct 2009 07:35
On Wed, 30 Sep 2009 09:50:44 -0700 (PDT), mkr5000 <mikerbgr(a)gmail.com> wrote: >You mean just like a simple half wave with another rectifier in >parallel but reversed? > >I never tried that -- didn't even think of it ! -- (or have even seen >it in many schematics >for that matter). (Of course, I wasn't looking for it, so maybe that's >the reason). > >I'll be darn -- except for the ripple compared to a bridge, it will do >the job just as well? > >Is it a good idea to match the rectifiers as far as forward and >reverse resistance? > >Using an over rated diode in a half wave is always a good idea too, >isn't it? > >Thanks. No need to match the diodes, but you need twice the PIV rating of the diode for a full bridge. |