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Is 30mV still acceptable as the lowest voltage for a linear power supply?
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babysitter:
They just suggest one of the "advanced" tests that separate a good lab power supply from a medium.

(I vaguely remember this being a suggestion of Bob Pease?)

Also test your supply with different loads, as in various R L C combinations. This might catch hints at the regulator getting a oscillator at certain situations. And attach a scope and use a MOSFET and pulse gen as a pulsed load, could also cause some ringing under just the right circumstances. Either there are none, or you get insight to harden against it, or you learn what to prevent.

Its preferrable to know about misbehaviour in advance instead of running into it unprepared.



duak:
Samuel, I suggest you vary your power supply voltage from 0 V to 100 mV while injecting the AC signal.  If there is a problem it is most likely to occur with the lowest digital codes into the DAC, eg. 0, 1, 2 etc.  I see the reference voltage is 4.096 V and that the DAC is 14 bits.  This gives 16384 steps of about 250 uV each.

The best way to observe a possible problem is with an oscilloscope.  A voltmeter may not show anything unusual because it is designed to filter noise.  However, it may show a different voltage than you expect but if the AC signal is disconnected you get the correct voltage.   The LM358 circuit I mentioned above was built by a friend to connect an Arduino to a servo amplifier that drove a steering wheel for a racing simulator.  He said it worked sort of OK in the corners but it was impossible to drive straight ahead.

Cheers,
bloguetronica:
Hi,

I haven't made the tests as you suggested yet, as I'm yet to find a suitable function generator. However, I did tests with that problematic CC load at 200mA, and saw no problems at all, even considering that the load was not grounded to earth. This seems to be very promising. I have two hypothesis:
- The op-amp is impervious to the relatively HV currents that are generated by the SPMS feeding the CC load;
- The relatively high resistance resistors are aiding to filter such noise.

I see a 20mVpp noise at the output when feeding the load, though. It is not an oscillation, as it is irregular. This issue doesn't manifest when testing the module with passive resistive load.

kind regards, Samuel Lourenço
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