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Quick validation experiment

A project log for Pocket Operator power supply (PO-PSU)

Micro USB to 3 V power supply for the Pocket Operator

Ben HolmesBen Holmes 07/18/2017 at 19:290 Comments


Using the first round of builds (minus the USB jack and with a couple of mod wires attached) the project has now been tested on some dummy loads.

Test setup

Results

With no load, there is 140 mV ripple current in the output.

Emulating one PO

Load100 Ω (30 mA)
Output Voltage2.98 V
Output ripple80 mV
Bench supply current20 mA
Efficiency(2.98^2/100)/(5*0.02) = 88.8 %

Emulating three POs

Load3 x 100 Ω in parallel (90 mA)
Output Voltage2.91 V
Output ripple60 mV
Bench supply current58 mA
Efficiency((2.91^2)/(100/3))/(5*0.058)= 87.6 %

This shows that PO-PSU can generate enough current for three POs without dropping the voltage significantly. The efficiency numbers seem good, although they are very approximate as I didn't measure the value of the resistors so they could be ±10%. The device is currently configured in burst-mode which offers better efficiency at low output currents, but it may be worth testing the device in pulse-skipping mode to see if there is a large loss in efficiency. Pulse-skipping mode is stated in the datasheet to offer better output ripple so would be nice to reduce the noise transmitted to the PO.

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