The one of suppression capacitors in the 7805's is a very interesting topic in itself... that values of input and output capacitors have been changing in the datasheets for years. The LM340T series of regulators (of which the 7805 is a direct descendant) used to need one 10uF tantalum capacitor in the input and another in the output. Being tantalum caps known for its flashy temperament, it drove some designs to very interesting failure modes. I have seen datasheets that put the capacitors as unnecessary and other as must-have. I feel much better with suppression as a must-have and with the small size of SMD components, it seems nonsense not to install them.
On Monday, March 30, 2015 at 7:33:57 AM UTC-3, Nick wrote: > > Just to re-iterate - solder a small 100nF capacitor between pins 1 & 2, > and another between pins 3 & 2, preferably on the underside of the PCB > directly to the 7805's solder pads. > > The symptoms you are seeing are almost certainly nothing to do with the > heatsinks etc - I'd put good money on this being a very common & classic > issue with 78xx & 79xx linear regulators whereby they break into VHF > oscillation and over-heat. This is extremely well documented and the > manufacturer's datasheets all say that the two suppression caps are not a > "nice to have" but are essential. Most of the datasheets actually specify a > 330nF input capacitor (between pins 1 & 2) but a 100nF works well too. > > Missing out these two capacitors is a basic error. > > Nick > > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/61443348-b83e-4708-8f09-8d7f5edd10d7%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
