using a synchronous rectifier in a boost circuit
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From: Jamie on 29 Jun 2010 18:05 On 6/29/2010 1:11 PM, Hammy wrote: > On Tue, 29 Jun 2010 10:04:27 -0700, Joerg<invalid(a)invalid.invalid> > wrote: > >> WangoTango wrote: >>> In article<vtij2694kou6ap4e7j17kraavkq7ifk56b(a)4ax.com>, spam(a)spam.com >>> says... >>>> On Tue, 29 Jun 2010 11:29:05 +0300, Paul Keinanen<keinanen(a)sci.fi> >>>> wrote: >>>> >>>>> On Tue, 29 Jun 2010 01:02:31 GMT, Jamie<jmorken(a)shaw.ca> wrote: >>>>> >>>>>> I am making a high power boost circuit (500watts+ with 12VDC input and >>>>>> 13.5VDC output). >>>>> That is more than 42 A. >>>>> >>>>> Are you sure that the ATX power supply will deliver that amount of >>>>> current _at_ 12 V ? >>>>> >>>> Paul makes a good point. >>>> >>>> It's usually the 5V rail thats good fo 30 to 50A the 12V is usually >>>> only good for 12A to maybe 20A. At least the ones I've seen. >>>> >>>> Oh and I wouldnt count on the supply to be able to delivery it for >>>> extended periods of time. >>>> >>> Or do it at all with no load on the +5V >>> >> >> It'll cost efficiency but I agree. The 12V rail diodes in most PC >> supplies are sort of skimpy. Probably because 12V only has to deliver >> peaks and once the hard disks or CD have spun up consumption goes back down. >> >> Of course Jamie could install bigger diodes on the 12V side but then he >> might as well swing the regulation loop over to 12V, disable everything >> else and set the new voltage divider resistor so that 13.5V comes out. > > Only if he could parallel more windings, I doubt the cooper could take > two to three times the rms current they were originally designed for > without excessive losses and causing thermal runaway on the > transformer. > > At this point it would probably be less trouble to buy an off the > shelf solution or build your own llc Half-bridge converter if your > feeling ambitious. ;-) Hi, The ATX supply I am working with is rated at 700watts and "80 Plus" efficiency, model OCZ700MXSP. It has dual rail 12V outputs (25Amps max on each rail, 552Watt max load rated on 12V) and the 5V rail is rated at 25Amps. I am boosting the 5V and 12V rails and combining them into a single ~13.5V adjustable rail (adjustable from 12V to 15V approximately). Good ATX power supply's are getting up to 1kW and beyond and have built in PFC and good efficiency. I was thinking about hacking into the ATX powersupply to change the 12V rails output regulation voltage to 13.5V, but as mentioned the 5V rail still needs a load to draw much power from the 12V rail. cheers, Jamie
From: Joerg on 29 Jun 2010 18:09 Jamie wrote: > On 6/29/2010 1:11 PM, Hammy wrote: >> On Tue, 29 Jun 2010 10:04:27 -0700, Joerg<invalid(a)invalid.invalid> >> wrote: >> >>> WangoTango wrote: >>>> In article<vtij2694kou6ap4e7j17kraavkq7ifk56b(a)4ax.com>, spam(a)spam.com >>>> says... >>>>> On Tue, 29 Jun 2010 11:29:05 +0300, Paul Keinanen<keinanen(a)sci.fi> >>>>> wrote: >>>>> >>>>>> On Tue, 29 Jun 2010 01:02:31 GMT, Jamie<jmorken(a)shaw.ca> wrote: >>>>>> >>>>>>> I am making a high power boost circuit (500watts+ with 12VDC >>>>>>> input and >>>>>>> 13.5VDC output). >>>>>> That is more than 42 A. >>>>>> >>>>>> Are you sure that the ATX power supply will deliver that amount of >>>>>> current _at_ 12 V ? >>>>>> >>>>> Paul makes a good point. >>>>> >>>>> It's usually the 5V rail thats good fo 30 to 50A the 12V is usually >>>>> only good for 12A to maybe 20A. At least the ones I've seen. >>>>> >>>>> Oh and I wouldnt count on the supply to be able to delivery it for >>>>> extended periods of time. >>>>> >>>> Or do it at all with no load on the +5V >>>> >>> >>> It'll cost efficiency but I agree. The 12V rail diodes in most PC >>> supplies are sort of skimpy. Probably because 12V only has to deliver >>> peaks and once the hard disks or CD have spun up consumption goes >>> back down. >>> >>> Of course Jamie could install bigger diodes on the 12V side but then he >>> might as well swing the regulation loop over to 12V, disable everything >>> else and set the new voltage divider resistor so that 13.5V comes out. >> >> Only if he could parallel more windings, I doubt the cooper could take >> two to three times the rms current they were originally designed for >> without excessive losses and causing thermal runaway on the >> transformer. >> >> At this point it would probably be less trouble to buy an off the >> shelf solution or build your own llc Half-bridge converter if your >> feeling ambitious. ;-) > > > Hi, > > The ATX supply I am working with is rated at 700watts and "80 Plus" > efficiency, model OCZ700MXSP. It has dual rail 12V outputs (25Amps max > on each rail, 552Watt max load rated on 12V) and the 5V rail is rated at > 25Amps. I am boosting the 5V and 12V rails and combining them into a > single ~13.5V adjustable rail (adjustable from 12V to 15V > approximately). ... Make sure your switchers are well current-limited if you do that, and don't motorboat against each other. > ... Good ATX power supply's are getting up to 1kW and > beyond and have built in PFC and good efficiency. I was thinking about > hacking into the ATX powersupply to change the 12V rails output > regulation voltage to 13.5V, but as mentioned the 5V rail still needs a > load to draw much power from the 12V rail. > Probably not if you swing the regulator feedback from 5V over to the 12V rail. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 29 Jun 2010 18:20 On Tue, 29 Jun 2010 11:28:04 -0700, Tim Wescott <tim(a)seemywebsite.com> wrote: >On 06/29/2010 11:04 AM, Jim Thompson wrote: >> On Tue, 29 Jun 2010 03:22:57 GMT, Jamie<jmorken(a)shaw.ca> wrote: >> >>> On 6/28/2010 6:32 PM, Vladimir Vassilevsky wrote: >>>> >>>> >>>> Jamie wrote: >>>> >>>>> Hi, >>>>> >>>>> I am making a high power boost circuit (500watts+ with 12VDC input and >>>>> 13.5VDC output). >>>> >>>> I wonder what is this for. >>> >>> Hi, >>> >>> I am using an off the shelf ATX power factor corrected 750Watt >>> powersupply as the 12VDC input, and then boosting this to ~13.5VDC for >>> charging lead acid batteries at 600watts+. This is part of my "ATX >>> power tower" project, a cheap home energy system in a PC case :) >>> >> [snip] >> >> Why not just tweak the ATX switcher directly to get to "13.5VDC"? >> >> Which, BTW, may not be adequate to charge a cool/cold lead acid >> battery. > >There's certainly a voltage/temperature relationship, but I'll be damned >if I can find my handy battery book! http://analog-innovations.com/SED/AlternatorRegulatorTC.pdf > >Hacking the supply sounds good, unless the intent is to have something >that is wholly external to the thing, to allow you to use any old ATX >supply of sufficient drive. > >It seems that if you're going to go to the trouble to misuse an ATX >power supply by building a 600W switcher to run off of an >already-regulated output, you could without too much more time and >expense just build an off-line switcher. ...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 | Obama: A reincarnation of Nixon, narcissistically posing in politically-correct black-face, but with fewer scruples.
From: m II on 29 Jun 2010 18:42 Jamie wrote: > Are there any boost PWM controller IC's out there that can > control an external sync rectifier (n-mosfet) to replace the boost > diode? PIC processor will do what you need, as will the Arduino. I have no experience with the PIC but I'm learning the Arduino. A universal battery charger using an Atmega8. That's pin compatible with the Arduino ATmega328. http://www.embedds.com/the-universal-multipurpose-battery-charger/ The code is copy and pastable into the Arduino compiler interface. An Arduino PWM driver http://reprap.org/wiki/PWM_Driver_1_1 A model railway controller, showing one pin driving a transistor: http://pcbo.dcs.aber.ac.uk/blog/2008/01/29/arduino-model-railway-control/ These fine people have many fine links: http://www.freeduino.org The Home page: http://www.arduino.cc/ The Arduino USB prototyping board is around 30 dollars US, with a microcontroller chip included. When you need more chips, they run anywhere from 3 to 6 dollars each. Youtube.com has a ton of Arduino related videos.
From: Hammy on 29 Jun 2010 18:45
On Tue, 29 Jun 2010 22:05:57 GMT, Jamie <jmorken(a)shaw.ca> wrote: >Hi, > >The ATX supply I am working with is rated at 700watts and "80 Plus" >efficiency, model OCZ700MXSP. It has dual rail 12V outputs (25Amps max >on each rail, 552Watt max load rated on 12V) and the 5V rail is rated at >25Amps. I am boosting the 5V and 12V rails and combining them into a >single ~13.5V adjustable rail (adjustable from 12V to 15V >approximately). Good ATX power supply's are getting up to 1kW and >beyond and have built in PFC and good efficiency. I was thinking about >hacking into the ATX powersupply to change the 12V rails output >regulation voltage to 13.5V, but as mentioned the 5V rail still needs a >load to draw much power from the 12V rail. > >cheers, >Jamie I would first try as Joerg suggests switching feedback to the 12V.If it does work you saved a lot of time and money. See his post below. If you want universal usages its pretty much a given PSU's once they start getting over 500W has some type of PFC. Not just because of THD regulations.Residential lines are only good for 15 to 20A. The typical SMPS with no PFC has a PF OF .55 TO MAYBE .65. At .65 the input cap is going to be small--> large 2f line ripple---> low DC input means high conduction losses. |