LED Brightness vs current

1. Purpose of study

- Use LED for powering 1.8-3.8V MCU with Li-ion battery

2. LED brightness vs current

- Jundouli Enterprise SJ-E54DxR24VU-S LED's

- 20mA : max. forward current

- LED dimming: PWM

3. LED driver

- Constant current: set by external resistor with 1.2V voltage source. The value of this resistor defines the amount of current flowing from this reference voltage source. The flowing current is copied by current mirror and multiplied by certain coefficient (usually 16) to set the driver’s output current. Driver latch just determines whether current source should be in on or off state.

- Current transmitted serially, shift register is used for reception.

- Driver dropout voltage: 0.4-0.7V

FFP: far-field pattern

Figure: LED brightness deviations from sample to sample

[Ref

[1] Svilainis, "LED forward current errors induced in video display tile's PCB