Testing linear regulators

Recently I was testing few different regulators and how they behave when you inject higher voltage (at low-ish current) to their outputs than what they are supposed to regulate. As it turns out (and as I kinda expected), many regulators are not very happy about this.

Testing them was kinda fun though. Let's take this 5-pin, 2.9x2.5mm sized one, very cheap 5v micropower (30mA max) regulator IFX20001;

That board is with standard 0.1" (2.54mm) grid. That should tell you about the scale here.

This one requires fairly large output capacitors to be stable (over 3.3uF), so I used 2 2.2uF caps in parallel. Those output caps are almost larger than the regulator itself! And of course I added small  (100nF) input cap.
Positive supply wire goes to left, ground to right and output downwards.

Unfortunately injected voltage goes straight to output with this chip (even if limited to well below 10mA) so this chip doesn't work too well for me here.

Another one I tried came in 8-pin 0.65mm pitch package. That does not fit very well on this prototyping board, but fortunately I keep old unpopulated project boards handy for just this kind of purpose. There is usually a part of them that can be used for just this kind of hacks;

I think this was originally for LED driver chip that I found out I don't really need so it was taken out from newer board revisions.

Here leftmost red wire is supply, center one is output and rightmost is voltage injection test lead, through 2k4 resistor. Resistors on left are feedback (with wire on top of chip being feedback wire), capacitor on left output capacitor (same 2.2uF as I used above, I do have full reel of them!) and wires on top are ground.

Neither of these chips was too happy to have higher voltage injected to their outputs, latter behaving a bit better. So if there is a risk of that, there needs to be diode in series to make sure nothing bad happens. Unfortunately I need output voltage to be 5v or slightly above so otherwise nice and smaller IFX, with its fixed 5v output voltage, does not work here. Ah well, so I spec the adjustable, larger and slightly more expensive other one.

Spec for what? Sorry fellas, but that is something I am not willing to share at this time.