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Two diode vs four diode rectification

Started by Peter Percival July 30, 2019
On 7/30/19 4:29 PM, default wrote:
> On Tue, 30 Jul 2019 16:06:06 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 7/30/19 10:42 AM, Bob Engelhardt wrote: >>> On 7/30/2019 10:04 AM, Peter Percival wrote: >>>> What is the advantage of a four diode bridge full-wave rectifier over >>>> a two diode full-wave rectifier.&Acirc;&nbsp; There must be some, else why accept >>>> the extra cost? >>>> >>> >>> You don't need a center tapped transformer with 4 diodes, you do need it >>> with 2. >> >> Also you get better transformer utilization because the whole winding >> conducts on both half-cycles. That improves the RMS-to-average ratio >> and reduces transformer heating (other things being equal). >> >> Cheers >> >> Phil Hobbs > > I've wondered about that. Seems to me you have two windings > conducting half the time with a CT so the average current and wire > size is smaller (or could be) and you only have two diode-drops > instead of four. So I'd expect the two diode version to be more > efficient (in low voltage power supplies at least, because the diode > drop represents a larger amount of the total V output). >
Efficiency is a slightly different issue. Neglecting diode drops, a half-wave supply has much worse copper losses because (a) you have to use smaller wire to get twice the secondary voltage, and (b) you're drawing twice the current for half the time. Item (b) costs you because the copper loss goes as I**2, so twice the current for half the time doubles the losses. At very low voltages the diodes become more important, but it's the transformer that costs the money. You can make a DC-DC converter for a dollar or so if that's an issue--a buck converter in both senses. ;) Cheers Phil Hobbs Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Peter Percival wrote:
> > What is the advantage of a four diode bridge full-wave rectifier over a > two diode full-wave rectifier. There must be some, else why accept the > extra cost? >
** The extra cost accrues with the two diode rectifier - cos the larger, centre tapped transformer needed increases cost more than two more diodes do. Two diode, full wave voltage doubler supplies are also common with direct off mains and transformer isolated supplies. Two vacuum diode, full wave systems were once the norm but soon became obsolete when silicon diodes appeared in the 1960s. .... Phil
With a bridge, only 2 diodes on 4 work.
So it preserve diode life.

Peter Percival a &Atilde;&copy;crit le 30/07/2019 &Atilde;&nbsp; 16:04&Acirc;&nbsp;:
> What is the advantage of a four diode bridge full-wave rectifier over > a two diode full-wave rectifier.&Acirc;&nbsp; There must be some, else why accept > the extra cost? >
Look165 is a Fucking Nut Case wrote:


> With a bridge, only 2 diodes on 4 work
** No, they all work.
> So it preserve diode life.
** False conclusion derived from a false assertion. What do people here reckon this nutter is? A Lebanese school boy? A Chinese compewter geek ? Escapee from an Indian mental asylum ? ..... Phil
On Tuesday, July 30, 2019 at 7:04:32 AM UTC-7, Peter Percival wrote:
> What is the advantage of a four diode bridge full-wave rectifier over a > two diode full-wave rectifier. There must be some, else why accept the > extra cost?
There's copper losses, and diode-drop losses, and core size difference. For a center-tapped winding, you need longer wire for the coil, and that raises the core size (unless you accept higher resistive heating from thinner wire). With a full-wave bridge, four diodes, you have TWO diode drops on each conducting half-cycle, but with a center-tapped two diode fullwave rectified circuit, there's only ONE diode drop. And, given a choice, a four-diode bridge and center-tapped coil gives you TWO power supplies. That's very convenient.
On Tuesday, July 30, 2019 at 3:26:29 PM UTC-5, Peter Percival wrote:
> jurb wrote: > > You can also use full wave WITH a center tap to get equal plus and minus voltages. Extra rectifiers mean shit - > > > > https://www.digikey.com/product-detail/en/taiwan-semiconductor-corporation/SFF1604G-C0G/SFF1604GC0G-ND/7358615 > > Two diodes sharing a cathode connection. Suppose one wants an > electrically identical pair of diodes but sharing the anode connection? > > > $1.12 and that's two of them. See the specs ? Like 200V., 16A, 35nS. > > > > Just how good of a rectifier do you need ? > >
They got them, it is just a matter of learning how to use their selector pages. Problem is they changed them and while it all still works it seems you can't get back to "More Filters" and have to back out and reapproach. They also have diodes in series in those packages. You want to know about filtering ? Well you got 420 volts at 3.5 amps, that means pretty much a resistance of 120 ohms. Here comes the math, now if you are going brute force there is no inductor, just a ton of capacitance. Figure out how much ripple you can handle and get a cap big enough to not discharge more than that in 1/60th of a second. That amount of ripple going into a choke will result in a certain voltage loss, which will be half the amplitude of the ripple. If you got 450 and 20 of ripple you got 440. that is what you'll get out of a choke. Into the next cap the whole thing is different because you have an impedance feeding that cap. The selection of the value of that next cap depends on the load and the variations in the load. Too much inductance you lose all semblance of regulation, less inductance you need bigger caps. If you have to much trouble figuring this out just adapt an extant design.
>> With a bridge, only 2 diodes on 4 work > > ** No, they all work.
You got him on semantics, he probably meant "conduct". Sure they are working when they are conducting, but they are also working when not conducting. They are blocking. When they no longer block they are considered not working.
>> So it preserve diode life. > > >** False conclusion derived from a false assertion.
Also ignores some logic on the subject. I won't be as mean as you but I will say it - ijiot ! YOU pick the diodes, they don't pick you ! And do you care if the diode is 50 cents or 60 cents ? I'm surprised I am even here. I did need a bit of a break though. Got any idea why the hell this Carver Receiver (MX-130) turns off the tuner when I turn off the speakers ? I decided to get away from it, and now I think I have a clue, it switches by relay, maybe somehow the 12 volt line is getting shorted... I'm just here to take a break from it. But thing is, I gotta write a book or something. These component values and all that, people give way too much attention to that.
jurb6006@gmail.com wrote:
> On Tuesday, July 30, 2019 at 3:26:29 PM UTC-5, Peter Percival wrote: >> jurb wrote: >>> You can also use full wave WITH a center tap to get equal plus and minus voltages. Extra rectifiers mean shit - >>> >>> https://www.digikey.com/product-detail/en/taiwan-semiconductor-corporation/SFF1604G-C0G/SFF1604GC0G-ND/7358615 >> >> Two diodes sharing a cathode connection. Suppose one wants an >> electrically identical pair of diodes but sharing the anode connection? >> >>> $1.12 and that's two of them. See the specs ? Like 200V., 16A, 35nS. >>> >>> Just how good of a rectifier do you need ? >>> > > They got them, it is just a matter of learning how to use their selector pages. Problem is they changed them and while it all still works it seems you can't get back to "More Filters" and have to back out and reapproach. > > They also have diodes in series in those packages. > > You want to know about filtering ? Well you got 420 volts at 3.5 amps, that means pretty much a resistance of 120 ohms. Here comes the math, now if you are going brute force there is no inductor, just a ton of capacitance. Figure out how much ripple you can handle and get a cap big enough to not discharge more than that in 1/60th of a second. > > That amount of ripple going into a choke will result in a certain voltage loss, which will be half the amplitude of the ripple. If you got 450 and 20 of ripple you got 440. that is what you'll get out of a choke. Into the next cap the whole thing is different because you have an impedance feeding that cap. The selection of the value of that next cap depends on the load and the variations in the load. > > Too much inductance you lose all semblance of regulation, less inductance you need bigger caps. > > If you have to much trouble figuring this out just adapt an extant design.
Please direct me to one ad tell me how to adapt it.
>
jurb = jerkoff fool @gmail.com wrote:


> >> With a bridge, only 2 diodes on 4 work > > > > ** No, they all work. > > You got him on semantics, he probably meant "conduct". Sure they are working when they are conducting, but they are also working when not conducting. They are blocking. When they no longer block they are considered not working. >
** All four diodes conduct - half of them during each half cycle. With two diode, full wave rectifiers its one diode per half cycle. The claim about extending diode life was bullshit Just like every single claim YOU post. ..... Phil
I was meaning that at half wave, only 2 diodes work.
For exemple : D1-D3 for +half wave, D2-D4 for -half wave.
In 2 diodes rectifier, the 2 always work.

Phil Allison a &Atilde;&copy;crit le 01/08/2019 &Atilde;&nbsp; 01:20&Acirc;&nbsp;:
> jurb = jerkoff fool @gmail.com wrote: > > >>>> With a bridge, only 2 diodes on 4 work >>> ** No, they all work. >> You got him on semantics, he probably meant "conduct". Sure they are working when they are conducting, but they are also working when not conducting. They are blocking. When they no longer block they are considered not working. >> > > ** All four diodes conduct - half of them during each half cycle. > > With two diode, full wave rectifiers its one diode per half cycle. > > The claim about extending diode life was bullshit > > Just like every single claim YOU post. > > > > ..... Phil > > >