Generally bipolars running in parallel are problematic because they exhibit a negative tempco. (they pass more current when hot) The net effect is that one will pass more than the rest, then, since it's passing more current it will get hotter and then pass even more current.... Until you get runaway and the magic smoke gets out. "Back in the day" when it was necessary to parallel bipolars I recall seeing some ballasting resistors in series with each transistor, Small value, high wattage to help mitigate this effect. Can't say I've see that in anything in the last 20 years or so though.... It's been my experience that _most_ TO220 packages connect the center pin to the tab. Can't think of an exception to that off the top of my head, but I'm sure somebody will be along shortly to prove me wrong :-) Either way, a multimeter might give you an answer faster than a support call.... -Denny On Thu, Jul 9, 2015 at 1:34 PM, Neil wrote: > Would any of you know if it's okay to parallel the collectors of > darlington transistors (TIP122) if they're all being driven with the > same (or very close to the same) signal? They'll most likely be > switched on/off rapidly, but what if I were to run them in the linear > region. I'm thinking I'll run into an issue with that, but not sure > about darlingtons. > > Also, the datasheet for OnSemi's TIP122 says the tab is connected to the > collector, but the Fairchild datasheet and ST's datasheet don't seem to > indicate either way. I have support calls in, but would anyone here > know if they are the same? The intention is to figure out if there's > any issue with some of these all bolted to a common aluminum heatsink. > > In case it helps... > http://www.onsemi.com/pub_link/Collateral/TIP120-D.PDF > > http://www.st.com/web/en/resource/technical/document/datasheet/CD00000911= ..pdf > https://www.fairchildsemi.com/datasheets/TI/TIP122.pdf > > Thanks. > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .