Bench Power Supply Question

[NivagSwerdna]

I have a TTi EL302RD Bench Power Supply...

If I set the output of one of the two channels to 12.00V 2.000A and then turn it on...

when attached to my gadget..  the display on the power supply varies...

11.94... 12.02V and 0.222 to 0.278A

I expected the voltage to remain constant at 12.00V whilst the current could vary (well below the 2A I set), why does the voltage vary so much?

I swapped channels and similar behaviour

My gadget has two converters...  one from 12V down to 5V and the other from 12V up to 70V

I'm sure this is trying to tell me something... just not sure what!

[bob91343]

The voltage cannot remain constant.  It will vary with load.  The amount if will vary will be, basically, the amount it would have varied without a regulator divided by the regulator's loop gain.

If a voltage would drop 1 Volt if unregulated, a regulator circuit with a loop gain of 100 will reduce that variation to 10 mV.

So maybe the readings you get are endemic to the particular equipment you have.  Read the specifications and see if it's within the parameters.

It's rare that a power supply would be regulated to much less than 0.5% but each design is different.  That would correspond to 60 mV change at 12 Volts.

Additionally, if your current limit is set too closely to the actual current, it may be holding the voltage down to maintain the limit.

[NivagSwerdna]

According to spec:
Load Regulation: <0.01% of maximum output for 90% load change, using remote sense.
Line Regulation: <0.01% of maximum output for 10% line change.
Ripple & Noise:(20MHz bandwidth) Typically <1mVrms, constant voltage mode.

[mikerj]

Additionaly 0.222 to 0.278A is the average current your device is taking, it could be taking much higher peak currents.

[tggzzz]

Where is the PSU measuring the voltage? If not at the same point as you are measuring, small resistances might account for the differences.

If possible, use remote sensing a.k.a. Kelvin connection.

[tooki]

Additionaly 0.222 to 0.278A is the average current your device is taking, it could be taking much higher peak currents.

^^ this.

Do you by any chance see the CC mode LED flicker on for a moment?

Try adding a decent size smoothing capacitor to the 12V power rail on the load, e.g. 1000μF and see if the behavior changes.

[NivagSwerdna]

So I did a couple of things... I changed the input side of one of the voltage regulators to have a 4.7uF 50V MLCC rather than the small Al electrolytic I had before... no change.  I then plugged in the scope to the input side and get...

PS
I did try a big 1000uF cap across the outputs of the bench supply and it didn't seem to change anything