Hi If you want the regulators to share the load equally when paralleled, they need to be a bit different than a +/-5% LM317
Bob On Jun 30, 2013, at 12:19 AM, Perry Sandeen <sandee...@yahoo.com> wrote: > > > Wrote: If you are in the US (maybe elsewhere) you can > request two free samples. > > That might work for projects on and two, but what > about projects three and onward? > > > Wrote: I suppose that the same philosophy > [paralleled regulators] would apply to getting more power with a 7805 farm. > > It does however with the general output rating of > 1 to 1.5 amps for each regulator it wouldn’t be very practical. It’s much > cheaper and simpler to use ones in > the 3 amp plus range. > > Wrote: A regulator needs to be specifically > designed for parallel operation. If it's not designed that way you will have a > very hard time with it. > > I’ve never heard of any three terminal regulator > designed for parallel operation. I believe > that all three terminal regulators use a pass transistor. When one uses them > in parallel they need a > slight resistance added to each pass transistor to prevent current hogging > just > as one had to do when paralleling power transistors in other high amperage > circuits. > > Wrote: It may be a bit more complicated than > that. You need some way to share the > load and you also need to make sure things are stable. > > The TI/National data sheet doesn't show anything > about paralleling regulators. The AD > data sheet shows 2 ft of #18 wire between each regulator and the load. > > I'm not enough of an analog guru to reverse > engineer that setup and figure out the stability constraints and transfer them > to 78xx type devices. > > > I stand corrected about the LM 1084 showing > paralleled regulators. However the data > sheet says it is pin compatible with the LM 317. So we get to the paralleled > regulator > circuits by a bit of a circuitous route. If we go to National Semiconductor > Linear > Brief 51 March 1981 titled “Add Kelvin Sensing and > Parallel Capability To 3-Terminal Regulators” it > shows how to parallel two or more three terminal LM 338 regulators. > > The stability problem is solved for us by the > Nation Semiconductor engineers. The 2 ft. of #18 wire for each regulator > provides the load balancing resistance needed. One could use an ordinary > resistor instead if it had the value of 30 > mili-ohms. > > The operation of all 3 terminal regulators are the > same. The internal circuitry looks at > the relationship between the output voltage and the *ground* terminal. As > the data sheets show, if we change that > relationship with resistor combinations we can manipulate the output voltage > to > our needs. > > For most low voltage applications one can usually > find a three terminal regulator that will fit the current needs, > > My original point was that the LM 1084 [$14] > IMNSHO is very expensive for what it does. By paralleling two far cheaper of > the LM 338 family one gets a larger ampacity of 10 amps instead of 7.5 amps > for > $3 to $5 instead depending on one’s scrounging abilities. > > In the end you pays your money and you make your > choices. > > Regards, > > Perrier > > > > ________________________________ > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.