Voltage Regulators in Parallel

That can be the next challenge, lol. This one at least seems stable over temperature and doesn't have a ballast resistor paradox.

We're trying to build the regulator equivalent of a lifted pick-up! Not some elegant thing

Use opamps (or trimpots!) to tweak the ground pin voltages to balance regulator currents. The +12 out will track the ground pin voltage.

Spice is wonderful for things like this, properly used. Well, with decent device models.

Sounds like the output voltage will have to be lifted above the worst-case output low voltage to give some room to maneuver with that scheme, or have a negative supply for the op amps if they're to balance automatically.

If say one output is sitting at 12.05 and the other at 11.95 with both GNDs grounded then you can't move the 12.05 down, the 11.95 can only go up.

The 78xx models are full discrete component models, what's inside those regulators is no mystery.

That is, in a purely fictitious universe. ;)

Cheers

Phil Hobbs

See which reg is the highest voltage and move the other one up to match.

Oh don't get technical.

A lot of models have truly grounded nodes inside, so you can't float them off ground. And some have independent current souces, so can be used as perpetual motion machines.

The bottom line is to select a voltage regulator that can handle the current - paralleling several inadequate regulators is a crap solution not worthy of analysis.

Not entirely. Some very simple integrated circuits are modelled at the transistor level. The Gummel-Poon transistor model doesn't capture inverted operation all that accurately, but mostly it is good enough.

If not here, where?

You do have to use that kind of model with discretion.

Flyguy has said something sensible for once. He's wrong of course - paralleling several very cheap voltage regulators can give you a cheap and nasty - but workable - solution and that would be worth analysing. There's usually an even cheaper and more elegant solution, but putting a good engineer on that kind of job is wasting their talent.

Analysis is somewhat useful; that's why we can call it a crap solution... Many systems having multiple point-of-load regulators show us an easy alternative, simply dividing the load into two or more blocks, and using a different regulator to power each block. As long as the input power is a single unregulated source, regulator outputs will track well-enough-for-logic.

And, in low-noise systems where correlation of multiple signals is important, having more than one regulator can help decouple power supply noise contributions.

Distributed 5V regulators was the design of choice used by HP with a raw source of 6V (?) and a shared 5V reference.

It was used for each PCB slot in a HP Multi-Programmer 19" Rack.

It was in my first custom design of a SCADA System with ADC/DAC/96 channel MUX based on two remote HP9825 calculators via serial RS485 datasets circa 1977. This also include Resistor controlled Voltage Lambda power Supplies using R-DAC's all controlled a mile away from the rocket launch pad.

I used to design SCADA systems, mostly for product pipelines. More like hundreds of miles over leased phone lines and sometimes RF out to oil rigs. Ever hear of TANO Corp?

Just switch them on one at a time. For example. Two regulators; one's on, one's off. Each sees a 50% duty-cycle. Expand as needed. Overlapping the on cycles might improve the switching noise.

Novel idea.

But not a good one. If you want a switching regulator design a proper one.

Sounds like you re-invented the multi-phase buck converter. Oft used for high end cpus in servers and desktops.

piglet

Not if they current limit, or share a heat sink.

Realistically, when a 3t reg is insufficient, design something better. Or split the loads.