>
>
> Dave King wrote:
>
> >
> > Just wondering if anyone has run across a working schematic
> > for a DC voltage regulator. Input range is 20-48 and required
> > output is 12vdc @ 10Amps with a max of say 15-20A.
> >
> > I'm looking at one schematic that has the required output but
> > is too narrow in the input voltage range. So if you know of a good
> > one please let me know.
> >
> > Tia
> >
> > Dave
>
> Are you looking for a switching or linear regulator?
>
> A classic Linear regulator is the multi 2N3055 pass transistors feed by
> a single 3055 driven by a 723.

> Most ARRL handbooks have the design including the transformer and
> rectifier/filter section.
> There are better transistors and FETs that can be substituted.
> You will need a MASSIVE heat sink, or forced cooled sink.
>  I have designed and built linear supplies with transistor and FET
> bricks for 100 amp+ performance.
>
> Tom
>
> --
>   *
>   |  __O    Thomas C. Sefranek   .....WA1RHPKILLspam@spam@ARRL.net
>   |_-\<,_   Amateur Radio Operator: WA1RHP  
>   (*)/ (*)  Bicycle mobile on 145.41, 448.625 MHz
>
> hamradio.cmcorp.com/inventory/Inventory.html
> http://www.harvardrepeater.org
>
>

> On 9/19/05, Dave King <.....KingDWSKILLspam.....shaw.ca> wrote:
>
>>>>>>Input range is 20-48 and required
>>>>>>output is 12vdc @ 10Amps with a max of say 15-20A.
>>>
>>>Can you tighten up that spec?  15-20A for how long?  With what
>>>sort of behavior on the output voltage?  Otherwise, you're looking
>>>at a 12V@20A power supply, which is twice the nominal 12V@10A...
>>
>>I need 10 amps (prob 99%)  but it should be capable of higher peaks
>>without letting the smoke out. The input voltage is going to be from 20-48
>>and not steady. I have no control over that one. I did look at telcom stuff
>>but the input seems pretty fixed around 48.
>>
>>Switching type is the only way to go on this as far as I can tell. It would
>>be
>>nice to keep the efficiency pretty high
>
>
>   this will produce a high output noise, of course
>
>
>>and the heat low.
>
>
>   360W of switching will not be low heat at all, so think to forced air cooling.
>
> I caught myself
>
>>looking
>>at Romans circuit the other night wondering if a few different bits might
>>make
>>it work.
>
>
> Nothing much appreciated than a good joke. Take a look on some
> schematics about how are designed PC power supplies. Then try to
> compute the switching circuitry for
> much higher current and lower input voltage. You need at least two
> power switching devices working in push-pull fashion. 20V and 400W
> means 20A switched. So you need some low Rds devices, else will be
> 0.1ohm Rds x 20Ax20A = 40W dissipated by one device. Also rectifiers
> must be carefully chosen, as well as coil designs. Avoiding core
> saturation is must at this power. If it's the first time for you, be
> prepared for a long and difficult project.
>
> success,
> Vasile
>

>
> However you are looking for a 240W power supply.  This is going to require
> some careful design and the right parts.  And yeah, it's going to cost more
> than a few transistors from the junk box and an RF choke.  This is also not
> a beginner's switching power supply.  Frankly, if you have to ask here, you
> probably shouldn't be attempting this by yourself.
>
> The wide input voltage range and high current suggest to me a dsPIC
> controlled multi-phase approach.  We have experience with this sort of
> thing.  Let me know if you want professional help.
>
>
> *****************************************************************
> Embed Inc, embedded system specialists in Littleton Massachusetts

> > Still the control is not so simple
> > since the basic of the PWM control is still lack of rigorous theory
> > to back up the analysis.
> > Cuk's averaging theory is quite okay
> > for practical analysis and PID control is still the most important
> > control method and is proved to be quite effective in practical
> > applications.
>
> Huh?  Exactly what theory do you think is missing?
>
> PID is certainly one control scheme.  It is readily implemented digitally so
> I don't see your point.

> > The major problem with
> > DSP/MCU based control is the speed of the ADC. It is still not
> > up to the requirement of the control application in quite a few cases.
>
> That is a consideration, and microcontroller control can't go as fast today
> as some of the top analog chips.  However, the dsPIC 10 bit A/D can sample
> at 500Khz on the first parts and over 1MHz on newer parts.  Switching
> frequencies of a few 100KHz are quite achievable with a dsPIC.  At 250KHz
> you get 120 instructions per pulse.  That's a lot.  If you go too fast the
> switching losses will start to be significant.  100-250KHz is a nice range
> for many practical switching power supplies.
>

>Having just designed and built a 0-50VDC 0-5A fully regulated LINEAR power
>supply I can quite rightly say that any work in this power range and
>above, serious consideration has to be given to getting the wasted heat
>out of the system.
>
>The power supply in question was designed for a magnet ramp supply, so
>noise was a serious consideration and therefore a switching supply was out
>of the question. The DC input voltage was 65VDC.
>
>The final design used an OPA541 pwr opamp as the series pass regulator,
>being driven by an ultra-stable, low-noise reference. Three MJ15003's in
>parallel were used as the pass elements. Current regulation was achieved
>using a fully floating/high side P-Channel MOSFET regulator. The unit was
>tested in abuse conditions to destruction several times. The two major
>concerns were the amount of latent heat that had to be removed and load
>dump due to the switching and disconnection of two very large electro
>magnets. This necessitated forced air cooling, both feed and drag fans at
>either end of the system and active surge clamping on the output to
>protect the power supply.
>
>For your application a similar configuration with an appropriate number of
>pass elements should be do-able.
>
>Nino.
>
>Vasile Surducan wrote:
>>On 9/19/05, Dave King <KILLspamKingDWSKILLspamshaw.ca> wrote:
>>
>>>>>>>Input range is 20-48 and required
>>>>>>>output is 12vdc @ 10Amps with a max of say 15-20A.
>>>>
>>>>Can you tighten up that spec?  15-20A for how long?  With what
>>>>sort of behavior on the output voltage?  Otherwise, you're looking
>>>>at a 12V@20A power supply, which is twice the nominal 12V@10A...
>>>
>>>I need 10 amps (prob 99%)  but it should be capable of higher peaks
>>>without letting the smoke out. The input voltage is going to be from 20-48
>>>and not steady. I have no control over that one. I did look at telcom stuff
>>>but the input seems pretty fixed around 48.
>>>
>>>Switching type is the only way to go on this as far as I can tell. It would
>>>be
>>>nice to keep the efficiency pretty high
>>
>>   this will produce a high output noise, of course
>>
>>>and the heat low.
>>
>>   360W of switching will not be low heat at all, so think to forced air
>> cooling.
>>I caught myself
>>>looking
>>>at Romans circuit the other night wondering if a few different bits might
>>>make
>>>it work.
>>
>>Nothing much appreciated than a good joke. Take a look on some
>>schematics about how are designed PC power supplies. Then try to
>>compute the switching circuitry for
>>much higher current and lower input voltage. You need at least two
>>power switching devices working in push-pull fashion. 20V and 400W
>>means 20A switched. So you need some low Rds devices, else will be
>>0.1ohm Rds x 20Ax20A = 40W dissipated by one device. Also rectifiers
>>must be carefully chosen, as well as coil designs. Avoiding core
>>saturation is must at this power. If it's the first time for you, be
>>prepared for a long and difficult project.
>>success,
>>Vasile
>
>
>

> The LT3800 is indeed an interesting product. The example application
> in the datasheet and the LT journal is only for lower power
> (12V, 75W and 3.3V/33W) so you need to adapt the design to suit
> your needs. 20A to 30A (or slightly higher) are practical limit
> of per phase in this kind of application. If more current
> is required, more interleaved channel will be required. For
> example,
> good Pentium 4 supply will be three to four channel and each channel
> will provide 20A to 30A to the CPU.
>
> Regards,
> Xiaofan

> Pet rocks, and analog SMPS ICs both share one truly endearing trait -
> once their makers have sorted out any early design problems (the lava
> state can be hard to deal with) neither crash or take occasional time
> out to get their act together after being subject to certain
> conditions within their specs
> but not anticipated by the designer. Depending on application this can
> be a significant factor.

>        RM
>