I'm trying to turn on/off the backlight of this LCD for the power saving when my ESP8266 goes to deep sleep. Because the ESP8266 has a maximum output current of 12mA and the LCD needs a current about 60mA, I decided to use a PNP transistor;(BC177.) According to the datasheet, it can handle currents about 100mA, so it seems to me that it's safe and good to use the following circuit:
simulate this circuit – Schematic created using CircuitLab
This page includes the state of the GPIOs when the ESP8266 goes to the deep sleep. I've tested this circuit and it works but I'm not sure if the circuit is appropriate and safe. Does turning off the backlight save power? The mentioned LCD has two other power supplirs which are unaffected when the ESP8266 goes to deep sleep.
Edit: We have the following information from the mentioned page:
- Backlight type: LED*4 current 60mA
- Voltage: working voltage VDDI=VDD= 2.8V-3.3V
- Total power consumption: 0.22W
With the above circuit, I'm getting about 2.96V collector voltage measured by oscilloscope.
Edit2: I found the datasheet for the LCD and uploaded it here.