I wanted to make a power supply providing roughly
+-2V) for small currents, given a whole range of different DC voltages (let's say about
For that I wanted to use an LM317L (link to pdf).
Setup: I hooked a adjustable benchtop PSU to
INPUT of the regulator and
GND, put a 100 ohm resistor between
OUTPUT and a
510 ohm resistor between
I choose these resistors to have an output voltage of
Vout = 7.6V = 1.25(1 + 510 / 100), while loading the regulator with
7.6 / (510 + 100) = 12.4 mA (the specs say the load needs to be at least
I omitted the capacitors for this experiment.
Issue: As I slowly increased the input voltage, the output voltage also increased up to about
8V. When increasing the input to about
25V, the output still had a stead
8V. Increasing the input to about
30V made the output increase to about
When I replaced the regulator with another (LM317L) one, I got a similar erratic behaviour again when the input exceeded
25V. Replacing it with same type regulator in the larger package (LM317 pdf) everything worked fine and I got around
8V for any input of
8-30V. Apart from the amount of output current they can provide, both of them should behave identically as far as I understand.
Can anyone point out what I'm doing wrong or what I possibly misunderstood?