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HiTech said:I was servicing a 12vDC to 120vAC inverter/charger and to my surprise the mfgr. has two LM317K (TO-3 case) regulator chips connected in parallel, apparently to increase current handling. I didn't know you could effectively connect them in parallel.(?)
HiTech said:I didn't get a chance to draw out the diagram, but this device is a "professional", high quality unit. The construction is near mil-spec, and a majority of the crucial components are custom mfgr'd. The company name is Wilmore. Oh, and the dang thing weighs well near 50 pounds with quite a large torroidal xformer in it!
According to the datasheet, the output voltage temperature coefficient is -1mV/C. If all parallel units start out sharing current approximately equally (as they should if they are all from the same lot, as Rio71 points out), then the negative tempco makes them inherently stable, temperature-wise. If one gets a little hotter than the rest, its output voltage will attempt to drop, pushing some of the current load to the other(s). This would not work with LM317s unless they all shared one feedback network (voltage divider). According to the Temperature Stability graph in the National datasheet, the reference tempco is also negative (above 25C), so they should be stable. Personally, I would never try this. If one device fails, the rest will fail (probably just shut down) in rapid succession under a heavy load.Rio71 said:hi,
yes, you can easyly paralleling linarregulators like lm317.
i have twelve L78S12CV parallel in a diy 25 ampere powersupply.
this is good 10years old an works perfectly.
i have the parts all three pins connectet "hard" together, no resistor between..
only one is really matters:
watch out that your regulators are absolutely from the same batch --> exactly same printing on it, especially the second line !!!
so differences from lot to lot are not present.