Forums » CircuitLab Support Forum

Ok, I know that a 7805 voltage regulator should have an input capacitor at least of 330nF “close to the input terminal”. However, in practice it (may) “work” without, especially when you have caps behind the rectifier - this leads to the question “How close is close?” in terms of mm / inches.

But testing a circuit with the 7805 in CL gives strange results, and, sorry, I think it’s a bug.

• Having an (even veeery) small cap (1fF) at the input works fine.

• Having no cap gives “Solver returned no data” error message.

Having the cap at the power supply doesn’t help either.

I did not try with other voltage regulators, but the Solver should not depend on a “visible and closely connected cap”, regardless which size.

Regards, Sancho

After testing your circuit it seems to me that the in of the 78XX needs to be connected to SOMETHING (e.g., a 1M resistor to GND or to V1, or a tiny, even 0F, capacitor) at ALL TIMES.