I have a very simple board, two layers, two gnd polygons, 8 analog inputs incoming from 8 potentiometers and 8 analog outputs. In the PCB are 2 resistors (R1||R2) between input and ouput. So, output just will drive 8 voltage dividers.
Board source supply is 24V, but input signals needs to be fed under 20V, so I used a MC78M12G regulator (12V). As this board outputs will be connected to 8 ADC in a PLC block, 2 bypass capacitors were connected at regulator input and regulator output.
Capacitor components have not arrived yet and board were sold with the rest of components.
Design considerations talks about capacitors will not be needed if it's used in a low current application.
Well, taking this into account, in order to get some advantage, I thougt to do some little and simple tests:
- only one active input (only one potentiometer is connected and its current is < 20mA),
- without connecting the board to the next block
- and then measuring its related output with a tester.
I thought the capacitor will be not needed -according to datasheet- and any signal freq will be passing through the circuit.
After switching on the board I can see how voltage output has unexpected low levels. I put the tester on the regulator output pin and I can see 4.6V.
Can the regulator be damaged due to Capacitors absence during switching on? Or can it be another factors?
This regulator it's able to drive until 500mA. I think the over current can not be the cause.