Rohde HMC8043 load regulation

[grouchobyte]

I recently picked up a RS HMC 8043 power supply as a complement to my a
Agilent linear supplies and another Rohde HMP2030. I need lots of power supplies when doing my metrology consulting projects.

 I am aware that switching supplies with linear post regulation like the 8403 are a little noisy at light loads, however this supply is marginal in that regard.  I  powered a cooling muffin fan with one channel 12 v @ 140 mA and the readback voltage was jumping a by +\- 5 mV on the display. I confirmed this with a scope.
Apparently that is specd and within the acceptable range.

I just wish it would do a better job or transient load regulation and do a little averaging on the display readout so it is not jumping around so much.

Comments?

@grouchobyte

[Messtechniker]

I  powered a cooling muffin fan with one channel 12 v @ 140 mA and the readback voltage was jumping a by +\- 5 mV on the display. I confirmed this with a scope.

Comments?

@grouchobyte

Back EMF from the fan?

[grouchobyte]

I  powered a cooling muffin fan with one channel 12 v @ 140 mA and the readback voltage was jumping a by +\- 5 mV on the display. I confirmed this with a scope.

Comments?

@grouchobyte

Back EMF from the fan?

Probably back EMF like you suggest. However I would expect the current to change with a variable load like a bad fan bearing and the current does go up and down as one would expect. In constant voltage mode it does a less than ideal job of maintaining constant voltage in light of the linear post regulation and its ability to regulate under transient load conditions. Even a large cap on the output fails to keep the voltage stable, although not a great idea if you want current limiting under transient load conditions.

@grouchobyte

 

[Kleinstein]

Some fans have quite some jumps in the current consumptions. This is not so much back EMF, but more like PWM like switching of a brush-less motor. If they save a penny on fast diodes this can include spikes from reverse recovery.  At least you can expect the current to go down to nearly 0 (e.g. 1 mA for the control circuit) at some times. Some fans also have extra capacitance to ease on the variable current - but an additional low ESR capacitance may have a negative effect on load regulation. If the fan includes speed regulation, it may even have an effective negative load impedance as it would need more current at lower voltage. A good supply should still be stable, as the input side of switched mode regulators can behave similar.

So the fan is actually a difficult load to a power supply and thus a good test. However the interesting part would be looking at the output with a scope.