EV5103 Datasheet, PDF (3/4 Pages) Global Mixed-mode Technology Inc – G5103 White LED Demo Board V1.0

Global Mixed-mode Technology Inc.
EV5103-10
When PWM dimming signal is low (almost equal to 0V):
I_LED = V_R1 / R1
V_R1 = V_FB – V_R2
V_R2 = I_R2 x R2
I_R2 = I_R3 – I_R4 - I_FB = (V_R3 / R3) – (V_R4 / R4) - I_FB = ((V_BIAS – V_FB)/R3) – (V_FB/R4) - I_FB
I_LED = (V_FB – R2 x (((V_BIAS – V_FB)/R3) – (V_FB/R4) - I_FB)) / R1
I_LED should be the design full current.
When PWM dimming signal is high (almost equal to V_{PWM_H}):
I_LED = V_R1 / R1
V_R1 = V_FB – V_R2
V_R2 = I_R2 x R2
I_R2 = I_R3 – I_R4 - I_FB = (V_R3 / R3) – (V_R4 / R4) - I_FB = ((V_BIAS – V_FB)/R3) – ((V_FB - V_{PWM_H})/R4) - I_FB
I_LED = (V_FB – R2 x (((V_BIAS – V_FB)/R3) – ((V_FB - V_{PWM_H})/R4) - I_FB)) / R1
I_LED should be a little negative current to make sure that LED is full dark.
In this demo board, GMT choose R1 = 27Ω, R2=120 KΩ, R3=240KΩ, R4=620KΩ.
When PWM signal is low:
I_LED = (1.2V – 120KΩ x (((3V – 1.2V)/240KΩ) – (1.2V/620KΩ) – 30nA)) / 27Ω = 19.7mA
When PWM signal is high:
I_LED = (1.2V – 120KΩ x (((3V – 1.2V)/240KΩ) – ((1.2V-3V)/620KΩ) – 30nA)) / 27Ω = -1.79mA
U2:
G914C is a micro power LDO regulator that make by GMT. It could regulate a +3VDC from a +3V
~ +5.5V power source. The +3VDC provide as V_BIAS for PWM dimming bias voltage, and provide
as the power of U3.
U3:
PIC12C509A is a 8bit micro controller that make by Microship. It is programmed as a PWM
dimming signal generator, and monitor 3 push button to change PWM duty and frequency for
dimming control.
Note: You need download the hex code to program a blank new PIC12C509A before solder it on demo board. You could
download this hex code from GMT web site http://www.gmt.com.tw
Jan 21, 2003
TEL: [phone]
http://www.gmt.com.tw
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