A different idea from A More Efficient Bridge Rectifier?
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From: Spehro Pefhany on 14 Feb 2010 15:53 On Sun, 14 Feb 2010 14:14:13 -0500, the renowned Hammy <spam(a)spam.com> wrote: >On Sun, 14 Feb 2010 13:02:20 -0500, "Paul E. Schoen" ><paul(a)peschoen.com> wrote: > >> >SNIP > >>Even better overall efficiency may be obtained by converting our electrical >>distribution system to DC. There will be less losses due to EMF effects. >>Most appliances can be made to use DC directly. Anything with a switching >>power supply can bypass the input rectifiers, and induction motors can be >>driven by PWM bridge controllers. And of course lighting and heating work >>as well on DC as AC. >> >>Paul >> >Electrical 101. > > Distrubution of DC is will generatae higher losses. I SQUARED * R. I think you skipped a lecture in E101 or something. ;-) Sinusoidal power and a resistive load gives the same RMS current and same power for the same resistance, so the I^2*R losses are exactly the same, all other things being equal. But there are AC losses from induced eddy currents and capacitive loading that occur ONLY with AC. Converting AC to DC for switching supplies for electronics and motor controllers either requires complex and expensive power factor correction circitry or draws current that increases I^2*R losses. The conversion itself eats a bit of power (in the bridge rectifier, for example). Also, the filter capacitors required for SMPSs are bulky and have relatively short lives. (OTOH, we can make doublers easily with AC input). But if, say, 300 VDC was available world-wide out of the wall, we could all have notebook computers that didn't require those stupid brick things. That would be good. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Joerg on 14 Feb 2010 17:18 Paul E. Schoen wrote: > "MooseFET" <kensmith(a)rahul.net> wrote in message > news:50cfb635-5888-428a-be43-efdc1cd3318d(a)x10g2000prk.googlegroups.com... > On Feb 13, 3:51 pm, Joerg <inva...(a)invalid.invalid> wrote: >> D from BC wrote: >>> In article <aabc57bc-4faf-4067-8ed2-df32f921f214 >>> @b9g2000pri.googlegroups.com>, kensm...(a)rahul.net says... >>>> On Feb 9, 5:06 pm, D from BC <myrealaddr...(a)comic.com> wrote: >>>>> My offline smps design has 3 parts making the most heat. >>>>> A power diode, a mosfet and a bridge rectifier. >>>>> I'm interested in any cookbook designs that replaces a bridge >>>>> rectifier. >>>>> Any pointers? >>>> Imagine the no input ripple version of the transformer coupled SEPIC >>>> circuit. >>>> ie: there are 3 windings the third being the isolated output. >>>> Now take the power MOSFET and replace it with a pair in series source >>>> to source. >>>> This circuit can be connected directly to the unrectified maines. It >>>> makes >>>> an isolated squarewavish wave form. This can then be run into a >>>> sychronous >>>> rectifier to make a DC output. >>>> All this involves no diode drops from the mains to the DC output. >>> Neato :) >> Except then you still have to replace the Schottky diode in the SEPIC >> with a synchronously controlled FET circuit ;-) > > Yes, it requires some good timing control on the fets and a pair of > perhaps 600V MOSFETs. This is two less of the costly parts than the > MOSFET bridge idea. > > It can be a PFC replacement for the transformer, bridge and capacitor > style power supply. The SEPIC doesn't put all that high of demands on > the core. It only has to hold the energy of one cycle plus a little > to make the current continuous to keep the ripple at zero. > > ------------------------------------------------------------------------- > > I still say that the bridge rectifier, or perhaps a doubler circuit, will > be the most efficient solution if one takes into account cost, complexity, > and reliability. One or two volts drop on 120 or 240 VAC mains is at most > 2% loss. > > Even better overall efficiency may be obtained by converting our electrical > distribution system to DC. There will be less losses due to EMF effects. > Most appliances can be made to use DC directly. Anything with a switching > power supply can bypass the input rectifiers, and induction motors can be > driven by PWM bridge controllers. And of course lighting and heating work > as well on DC as AC. > .... and then it gets cold, uncle Leroy plugs in the old space heater, the one that didn't have a safety thermodisk yet ... phsss ... *PHUT* .... li'l meltdown on the carpet but uncle Leroy has dozed off by now ... smoke alarms blare ... sirens start wailing at the engine company 17 ... -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Hammy on 14 Feb 2010 17:24 On Sun, 14 Feb 2010 15:53:33 -0500, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >I think you skipped a lecture in E101 or something. ;-) > >Sinusoidal power and a resistive load gives the same RMS current and >same power for the same resistance, so the I^2*R losses are exactly >the same, all other things being equal. > >But there are AC losses from induced eddy currents and capacitive >loading that occur ONLY with AC. Converting AC to DC for switching >supplies for electronics and motor controllers either requires complex >and expensive power factor correction circitry or draws current that >increases I^2*R losses. The conversion itself eats a bit of power (in >the bridge rectifier, for example). > >Also, the filter capacitors required for SMPSs are bulky and have >relatively short lives. (OTOH, we can make doublers easily with AC >input). > >But if, say, 300 VDC was available world-wide out of the wall, we >could all have notebook computers that didn't require those stupid >brick things. That would be good. > > >Best regards, >Spehro Pefhany Opps Your right. I'll try and redeem myself. The reason DC transmission is seldom used is because of DC transmission losses. For example how would you get 300Vdc to every residence say at +/- 20%? The DC losses in the transmission line make that difficult and costly to implement on a wide scale. Whereas with AC start out at a large voltage and with a relatively small current reduces the DC losses and just use a transformer to service a section of residence. Hopefully I didn't stick my foot any further down my throat. I guess I should be thankful you caught it and not Phil :-) He wouldnt be so civil.
From: Jim Thompson on 14 Feb 2010 17:29 On Sun, 14 Feb 2010 14:18:51 -0800, Joerg <invalid(a)invalid.invalid> wrote: >Paul E. Schoen wrote: >> "MooseFET" <kensmith(a)rahul.net> wrote in message >> news:50cfb635-5888-428a-be43-efdc1cd3318d(a)x10g2000prk.googlegroups.com... >> On Feb 13, 3:51 pm, Joerg <inva...(a)invalid.invalid> wrote: >>> D from BC wrote: >>>> In article <aabc57bc-4faf-4067-8ed2-df32f921f214 >>>> @b9g2000pri.googlegroups.com>, kensm...(a)rahul.net says... >>>>> On Feb 9, 5:06 pm, D from BC <myrealaddr...(a)comic.com> wrote: >>>>>> My offline smps design has 3 parts making the most heat. >>>>>> A power diode, a mosfet and a bridge rectifier. >>>>>> I'm interested in any cookbook designs that replaces a bridge >>>>>> rectifier. >>>>>> Any pointers? >>>>> Imagine the no input ripple version of the transformer coupled SEPIC >>>>> circuit. >>>>> ie: there are 3 windings the third being the isolated output. >>>>> Now take the power MOSFET and replace it with a pair in series source >>>>> to source. >>>>> This circuit can be connected directly to the unrectified maines. It >>>>> makes >>>>> an isolated squarewavish wave form. This can then be run into a >>>>> sychronous >>>>> rectifier to make a DC output. >>>>> All this involves no diode drops from the mains to the DC output. >>>> Neato :) >>> Except then you still have to replace the Schottky diode in the SEPIC >>> with a synchronously controlled FET circuit ;-) >> >> Yes, it requires some good timing control on the fets and a pair of >> perhaps 600V MOSFETs. This is two less of the costly parts than the >> MOSFET bridge idea. >> >> It can be a PFC replacement for the transformer, bridge and capacitor >> style power supply. The SEPIC doesn't put all that high of demands on >> the core. It only has to hold the energy of one cycle plus a little >> to make the current continuous to keep the ripple at zero. >> >> ------------------------------------------------------------------------- >> >> I still say that the bridge rectifier, or perhaps a doubler circuit, will >> be the most efficient solution if one takes into account cost, complexity, >> and reliability. One or two volts drop on 120 or 240 VAC mains is at most >> 2% loss. >> >> Even better overall efficiency may be obtained by converting our electrical >> distribution system to DC. There will be less losses due to EMF effects. >> Most appliances can be made to use DC directly. Anything with a switching >> power supply can bypass the input rectifiers, and induction motors can be >> driven by PWM bridge controllers. And of course lighting and heating work >> as well on DC as AC. >> > >... and then it gets cold, uncle Leroy plugs in the old space heater, >the one that didn't have a safety thermodisk yet ... phsss ... *PHUT* >... li'l meltdown on the carpet but uncle Leroy has dozed off by now ... >smoke alarms blare ... sirens start wailing at the engine company 17 ... There Joerg goes again *PHUT* *PHUT* *PHUT* *PHUT* *PHUT* *PHUT* Whew! Sure glad I don't live next door ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Jim Thompson on 14 Feb 2010 17:31
On Sun, 14 Feb 2010 17:24:19 -0500, Hammy <spam(a)spam.com> wrote: >On Sun, 14 Feb 2010 15:53:33 -0500, Spehro Pefhany ><speffSNIP(a)interlogDOTyou.knowwhat> wrote: > > > >>I think you skipped a lecture in E101 or something. ;-) >> >>Sinusoidal power and a resistive load gives the same RMS current and >>same power for the same resistance, so the I^2*R losses are exactly >>the same, all other things being equal. >> >>But there are AC losses from induced eddy currents and capacitive >>loading that occur ONLY with AC. Converting AC to DC for switching >>supplies for electronics and motor controllers either requires complex >>and expensive power factor correction circitry or draws current that >>increases I^2*R losses. The conversion itself eats a bit of power (in >>the bridge rectifier, for example). >> >>Also, the filter capacitors required for SMPSs are bulky and have >>relatively short lives. (OTOH, we can make doublers easily with AC >>input). >> >>But if, say, 300 VDC was available world-wide out of the wall, we >>could all have notebook computers that didn't require those stupid >>brick things. That would be good. >> >> >>Best regards, >>Spehro Pefhany > >Opps Your right. > >I'll try and redeem myself. > >The reason DC transmission is seldom used is because of DC >transmission losses. For example how would you get 300Vdc to every >residence say at +/- 20%? The DC losses in the transmission line make >that difficult and costly to implement on a wide scale. > >Whereas with AC start out at a large voltage and with a relatively >small current reduces the DC losses and just use a transformer to >service a section of residence. > >Hopefully I didn't stick my foot any further down my throat. > >I guess I should be thankful you caught it and not Phil :-) >He wouldnt be so civil. DC is primarily used only for long distance UHV distribution. .... Except in some old parts of New York City ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |