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Two diode vs four diode rectification

Started by Peter Percival July 30, 2019
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?

-- 
"He who will not reason is a bigot;
he who cannot is a fool;
he who dares not is a slave."
  - Sir William Drummond
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.  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.
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

$1.12 and that's two of them. See the specs ? Like 200V., 16A, 35nS. 

Just how good of a rectifier do you need ?
jurb6006@gmail.com 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 > > $1.12 and that's two of them. See the specs ? Like 200V., 16A, 35nS. > > Just how good of a rectifier do you need ? >
What I need is a bridge (the transformer I'm considering doesn't has a centre tapped secondary) that will handle 420 volts, 3.5 amps. Also, I'd like recommendations for capacitor and inductor values for smoothing. -- "He who will not reason is a bigot; he who cannot is a fool; he who dares not is a slave." - Sir William Drummond
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.  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 -- 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
Phil Hobbs 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.  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 >
Thank you. That's the sort of think I was after.
On Tue, 30 Jul 2019 20:17:12 +0100, Peter Percival
<peterxpercival@hotmail.com> wrote:

>jurb6006@gmail.com 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 >> >> $1.12 and that's two of them. See the specs ? Like 200V., 16A, 35nS. >> >> Just how good of a rectifier do you need ? >> > >What I need is a bridge (the transformer I'm considering doesn't has a >centre tapped secondary) that will handle 420 volts, 3.5 amps. Also, >I'd like recommendations for capacitor and inductor values for smoothing.
check out: http://www.valvewizard.co.uk/smoothing.html Very few amps use Pi filters these days (capacitor inductor capacitor) that's more common back when capacitors were these huge metal cans with aluminum foil paper and oil and had a rating of only ~1-10 microfarads. Today they use electrolytic caps with much higher capacity and avoid the expense of big heavy inductors. http://education.lenardaudio.com/en/14_valve_amps_6.html
jurb6006@gmail.com 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 ? >
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.&#2013266080; 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).
On Tue, 30 Jul 2019 21:26:25 +0100, Peter Percival
<peterxpercival@hotmail.com> wrote:

>jurb6006@gmail.com 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?
They make those too. Or you could use half of a full wave bridge if heat sinking is a consideration. You're not designing this for mass production where every penny is going to be counted.
> >> $1.12 and that's two of them. See the specs ? Like 200V., 16A, 35nS.
I thought you were working at ~400 V? The storage time is insignificant in linear mains supplied transformers - it becomes significant when you are rectifying square waves or high frequencies or both.
>> >> Just how good of a rectifier do you need ? >>
Not very for 50-60 cycles. A little extra head-room on the voltage is nice to accommodate power line surges without shorting the diodes.