Dual polarity supply -- no center tap
in [Design]
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From: MooseFET on 30 Sep 2009 21:07 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.
From: David Eather on 1 Oct 2009 09:21 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 .
From: Phil Hobbs on 1 Oct 2009 16:07 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 -- 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: Phil Hobbs on 1 Oct 2009 16:12 MooseFET 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. If you double the capacitance with the two half-wave circuits, you get the same ripple with only 1/4 as many diodes, and the + and - supply voltages will match better. Transformer utilization is the same as well, if the two supplies are loaded about the same, but if the + supply is lightly loaded your approach is probably superior. (Switching the bridges around would suit a lightly loaded - supply.) 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: MooseFET on 1 Oct 2009 21:06
On Oct 1, 1:12 pm, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > MooseFET 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. > > If you double the capacitance with the two half-wave circuits, you get > the same ripple with only 1/4 as many diodes The ripple in that case is still 60Hz and the two ripples have their peaks out of step. It is the same amplitude however. If the diodes are in the form of complete bridge packages, The package count comes out good for my version. >, and the + and - supply > voltages will match better. Transformer utilization is the same as > well, if the two supplies are loaded about the same, but if the + supply > is lightly loaded your approach is probably superior. (Switching the > bridges around would suit a lightly loaded - supply.) I used the other version when I needed to make a lot of +12 and not much -12 in a supply. It worked nicely. > > 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 |