PCB Assembly Services - Screaming Circuits: Point Of Load Power Supply


Point Of Load Power Supply

POL or Point-of-load seems to be a hot topic these days. Just to be clear, I'm not talking about Internet traffic or construction - although point of load, as well as load bearing capacity are also quite important in Pth05060_on_boardthose areas as well. I'm referring to power distribution and regulation in electronics systems.

It wasn't that long ago when most things could be run off of +5 volts or +/- 12 volts. That was easy. You just have three power busses and a ground bus. You might have to double some up or take care what is next to what to make sure you have enough current carrying capacity and to reduce noise, but it was fairly easy.

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Now though, you've got 5 volt, 3 volt, 1.8 volt, 1.3 volt, 1.2 volt, 12 volt, 48 volt... depending on your application. You just can't have that many different power busses. Well, you could but I won't let you. In comes point of load. You run a higher voltage bus around and at each major section of the circuit with a different voltage requirement, you drop in a little switching regulator or DC to DC converter. A few years ago, this was much more difficult to do because switching regulators were bigger and a lot more expensive. Linear regulators are too inefficient in most cases to be used as point of load regulators, especially when the difference between sours and load voltage is great.

We've been running across a lot of these point of load modules lately. I wrote a bit about them a while back in this post about daughter boards. There's even an industry standards movement: Point of Load Alliance. If you design in a part from one alliance member, you won't be single-sources which is a good thing. Most of the modules are pretty clunky, but some are getting down into actual chip form factors.

By using these nice Little gizmos, you can have one or two main busses feeding a number of POLPol_two_types regulators and then localized sub-section busses feeding processors FPGAs and other components that have different voltage requirements. The parts come in both surface mount (usually a BGA type surface  mount connection) or thru-hole form factors. Here's an example of a design that uses two nearly identical modules, one surface mount and one thru-hole.

Ironically, a form of point-of-load was pretty popular thirty years ago. The ancient S-100 bus computers 664pxaltair_8800_computer had +8 volt and +/- 18 volt main busses and used local 5 volt and +/- 12 volt regulators on the individual plug in cards or sections on those cards. Rumor has it, the first "personal computer", the Altair 8800 used 8 volt and +/- 18 volt because they got a good deal on power supplies and could buy them cheaper than buying or building a big linear +5 volt and +/- 12 volt supply. This forced all of the cards to have localized regulation. It also prevented problems such as bus voltage sagging under high load conditions too, but they did it (allegedly) just because of cost and convenience.

Duane Benson
Those who do not remember the past may get lucky enough to repeat it


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Maybe one day there will be a universal standard for all electrical currents. It tends to get difficult with the used SMT machines that we sell around the world. Good thing that most clients understand currents.

www.mskennedy.com offers useful information and datasheets on their Point of Load (POL) applications. MS Kennedy has created the first hermetic, hi-rel switching regulators product line.

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