Ben Holmes
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
- Oscilloscope on output
- Bench supply powering the board
- 100 Ω resistors mimicking a PO (V=IR, 3=0.03*R, R=100Ω)
Results
With no load, there is 140 mV ripple current in the output.
Emulating one PO
| Load | 100 Ω (30 mA) |
| Output Voltage | 2.98 V |
| Output ripple | 80 mV |
| Bench supply current | 20 mA |
| Efficiency | (2.98^2/100)/(5*0.02) = 88.8 % |
Emulating three POs
| Load | 3 x 100 Ω in parallel (90 mA) |
| Output Voltage | 2.91 V |
| Output ripple | 60 mV |
| Bench supply current | 58 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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