Global Mixed-mode Technology Inc.
Components List
Designation
R1
R2
R3
R4
C1
C2
C3
C4
C5
EV5103-10
Qty
1
1
1
1
1
1
1
1
1
Value& P/N
27
Ω
_1%
120K
Ω
_1%
240K
Ω
_1%
620K
Ω
_1%
4.7µF
0.1µF
1µF
1µF
0.1µF
10µH/0.5A IDC
(LQH32CN100K31)
10µH/0.5A IDC
(976AS-100M)
0.5A/30V(MBR0530)
G5103
G914C
PIC12C509A
NSCW100
Description
Current Sense Resistor
Feedback Resistor (recommend)
PWM Dimming Control Bias Resistor
PWM Dimming Control Mixer Resistor
Input Capacitor
Output Capacitor
Input Capacitor
Output Capacitor
Bypass Capacitor
Inductor
Inductor
Std
Vendor
TAIYO YUDEN
MURATA
TOKO
L1
1
D1
U1
U2
U3
SW1~3
LED1~4
1
1
1
1
3
4
Schottky Diode
ON Semi
Micro Power Step-up DC/DC Converter
Global Mixed-Mode Technology
Mirco power LDO regulator. V
OUT
=3.0V
http://www.gmt.com.tw
8 bits micro-controller
Miocrochip
Push button switch
Std
White LED
NICHIA corporation
Circuit Description
The demo board is configured as a constant current supply. Current regulation is accomplished by regulating
the voltage across a current sense resistor R1. For dimming the LEDs is to inject a pulse width modulated
(PWM) voltage for analog dimming. With this method, the PWM control voltage is converted to its equivalent
analog control voltage. The demo board is designed so that the negative duty cycle from 0% to 100% varies
the LED current from 0mA to 20mA. The output current increases as the duty cycle increases. Use the
equation below to calculate the correctly resistor values.
V
BAT
:
V
BIAS
:
R1:
R2:
R4:
Li-Ion battery power input, bypass to ground with a 4.
7
µF MLCC capacitor.
+3.0VDC provide a PWM dimming DC bias voltage. It is generated by G914C from V
BAT
.
is LED current sense resistor. R1= 0.60V / I
LED,MAX
= 0.60V / 20mA = 30Ω
is feedback resistor, 120KΩ is recommended.
is PWM dimming control mixer resistor. The value is depended on PWM dimming control signal
amplitude. R4= (V
H
- V
L
) / (0.6V / 120KΩ). (maximum value, a little small value could be used)
For 3.0V PWM control signal: R4= 3V / (0.6V / 120KΩ) = 600KΩ.
For 3.3V PWM control signal: R4= 3.3V / (0.6V / 120KΩ) = 660KΩ.
For 5.0V PWM control signal: R4= 5V / (0.6V / 120KΩ) = 1MΩ.
R3:
is PWM dimming control bias resistor. The value is depended on V
BIAS
voltage.
R3=( V
BIAS
– V
FB
) /[(0.6V/120 KΩ)+(V
FB
/ R4)].
For 3VDC V
BIAS
:= (3.0V – 1.2V) / [(0.6V/120 KΩ)+(1.2V / 600 KΩ)] = 257 KΩ.
For 3.3VDC V
BIAS
:= (3.3V – 1.2V) / [(0.6V/120 KΩ)+(1.2V / 660 KΩ)] = 308 KΩ
For 5VDC V
BIAS
:= (5.0V – 1.2V) / [(0.6V/120 KΩ)+(1.2V / 1000 KΩ)] = 612 KΩ
After choose suitable resistors, designer should check I
LED
again.
Jan 21, 2003
TEL: 886-3-5788833
http://www.gmt.com.tw
2
GMT [ GLOBAL MIXED-MODE TECHNOLOGY INC ]
