oyvstok
Posts: 1
Joined: Tue Jun 26, 2018 8:43 pm

Display backlight current

Tue Jun 26, 2018 8:46 pm

I'm using the RPi display for a project with a custom PCB, and I wonder if someone knows the current the RPi display driver board gives the backlight? It seems to be much brighter on the RPi than my own PCB.

Thanks

W. H. Heydt
Posts: 8772
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Display backlight current

Thu Jul 12, 2018 6:03 am

I believe the total current draw for the device at full backlight is about 250mA.

helioz2000
Posts: 3
Joined: Sun Jul 22, 2018 2:19 am
Location: Australia
Contact: Website

Re: Display backlight current

Sun Jul 22, 2018 2:52 am

Have conducted a test on the actual current consumption of Pi with Touch Screen of the 7" official version connected to DSI and Touch connections via I2C.
The installed OS is Raspbian Stretch Lite (4.14.56-v7+) and for this test the display shows a white background with "Hello World" in the centre. The Pi (3 Model B Rev 1.2) was connected to my network via WiFi and I was logged in from a remote ssh terminal to conduct the tests.

Power consumption is as follows:
Pi only, display power disconnected: 260mA
Pi + Display with varying levels of brightness:
0 = 325mA
10 = 325mA
25 = 345mA
50 = 380mA
75 = 420mA
100 = 460mA
125 = 510mA
150 = 590mA
160 = 635mA
175 = 730mA
200 = 765mA
225 = 740mA
255 = 680mA
The brightness levels were controlled with "echo 100 > /sys/class/backlight/rpi_backlight/brightness"

The highest brightness off the display occurs with a brightness setting of 200, further increases cause the display to go dimmer.

Deducting the Pi's base power consumption, I would say the display draws between 65mA and 505mA, depending on the brightness setting.

I was also curious to see if complete blanking of the display reduced the power consumption so I used "echo 1 > /sys/class/backlight/rpi_backlight/bl_power" to switch the display off in the same way as most screen savers, but the power consumption remained at 325mA, same as when the display brightness is set to 0.

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