People are reporting that a modification of RG2 to a switch mode variant sees reductions in power consumption between 10 to 25%. I will not be looking to replace the 1.8V regulator as it seems to only offer marginal improvement on top of replacing RG2.
I have chosen to replace this regulator with the RECOM R-783.3-0.5 high efficiency/low ripple switching supply. It offers very high efficiency (91%) at it's minimum voltage limit (4.75V) so at 5V it should offer about the same. It has the following pinout:
25.7mA - After "sudo halt"Comparing that to the previous tests, we achieve a load reduction of 13.5-16.4% (27.2% when halted) which is nothing short of awesome.
93.6mA - Idle (avg)
96.2mA - Idle (avg) (with HDMI connected)
136.0mA - Running stress test
138.8mA - Running stress test (with HDMI connected)
But we can't stop there. All this power has gone to my head. We can now enable a power saving mode which will throttle back the CPU when idling.
Install the following (note, you will need a USB NIC on a hub to connect to the internet if you have removed the LAN9512):
sudo apt-get install cpufrequtils
Edit /boot/config.txt and insert the following values:
force_turbo=0 #turns on frequency scalingThen you can now set the 'ondemand' governor. This will alter the CPU clock speed depending on load.
arm_freq=700 #sets max frequency
arm_freq_min=100 #sets min frequency
cpufreq-set -g ondemand
Now reboot. If you don't perform all of this before rebooting (contrary to what's on the site linked above), you will have issues with the pi rebooting because the CPU frequency is too low (as the Broadcom's watchdog time kicks in) or USB devices acting bizarre.
You can check you current speed in Hz with "cpufreq-info"
Now for the stats:
90.5mA - Idle (avg) - 100MhzWhile this isn't a significant decrease, it still provides some benefit over not having it on and it doesn't take too much effort to enable it.
93.6mA - Idle (avg) (with HDMI connected) - 100Mhz
134.9mA - Running stress test - 700Mhz
137.93mA - Running stress test (with HDMI connected) - 700Mhz