🚀 go-pugleaf

In article <9212170609.AA07808@gaak.LCS.MIT.EDU>, jpexg@gaak.LCS.MIT.EDU (John Purbrick) writes...
> 
>I want to set up a power supply delivering more current than an integrated
>voltage regulator (LM78xx if fixed, or LM317 if variable) will provide. It
>seems valid to parallel as many of the relevant component as I need to get
>the current; certainly they won't all pass the same current, and the voltage
>out will drop if the initially-highest regulator starts to overload, but it
>should settle to some lower voltage as other regulators start to conduct 
>more. It seems that this would apply whether the overload was caused by 
>overcurrent or overheating. And when all the regulators are conducting, the 
>output should be no lower than the lowest output would have been if they were 
>wired individually.
> 
	The technique works well, but you need two things additional.

	A/ You need what are called ballast resistors to balance the current
	   delivered by each regulator. Typically you should have something
	   on the order of 0.5 volts or so drop in each resistor at full
	   current. (Note that this requires a regulator that lets you use
	   a remote voltage sensing point.)

	B/ It's a good idea to add a fuse in the output of each regulator,
	   so that if one regulator shorts, it doesn't take the rest out with
	   it.

	For the case where load was reasonably constant, I would just figure
	each resistor for a 0.5 volt drop, then put a diode between the
	normally grounded pin of the 3-pin regulator. The nominal 0.5 volt
	drop in the diode would make up for the 0.5 volt drop in the ballast
	resistors. For highly varying loads, use an appropriate zener and
	resistor to bias the normally grounded pin of the regulator.

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