CPC9909 Datasheet, PDF (9/12 Pages) IXYS Corporation – High Effciency,Off-line, High Brightness LED Driver

INTEGRATED CIRCUITS DIVISION
CPC9909
2.10 Linear Dimming
A linear dimming function can be implemented by
applying a DC control voltage to the LD pin. By varying
this voltage from 0V to V_CS(high), the user can adjust
the current level in the LEDs which in turn will increase
or decrease the light intensity. The control voltage to
the LD pin can be generated from an external voltage
divider network from V_DD. This function is useful if the
Figure 3 Typical Linear Dimming Application Circuit
user requires LED current of a particular level, and
there is no exact R_T value available. Note that applying
a voltage higher than the current sense threshold
voltage to the LD pin will not change the output current
due to the fixed internal threshold setting. When the
LD pin is not used, it should be connected to V_DD.
Fuse F2
2A
AC Input
90 - 265V_rms
NTC1
BR1
AC -
AC +
D1
BYV26B
C1
0.1μF
400V
C1
22μF
400V
HB LEDs
350mA
L1
4.7mH
IXTA8N50P
R4
0.56Ω
LD
Monitor
R1
402kΩ
CPC9909
V_IN
CS
GND
GATE
R_T
LD
V_DD
PWMD
C1
2.2μF
16V
C1
0.1μF
25V
R2
51kΩ
RA1
5.0kΩ
2.11 PWM Dimming
Pulse width modulation dimming can be implemented
by driving the PWMD pin with a low frequency square
wave signal in the range of a few hundred Hertz. The
PWMD signal controls the LED brightness by gating
the PWM gate driver output pin GATE. The signal can
be generated by a microcontroller or a pulse generator
with a duty cycle proportional to the amount of desired
light output.
Figure 4 Buck Driver for PWM Dimming Application Circuit
V_IN
12 - 30V_DC
10μF
50V
D1 Schottky
40V
220μH
Q1
CPC9909
V_IN
CS
GND
GATE
R_T
LD
V_DD
PWMD
402kΩ
R1
0.27Ω
0.1μF
50V
HB LEDs
900mA Max
ASMT-Mx00
CPC1001N*
PWM
*Optional Isolation
2.12 Combination Linear and PWM Dimming
A combination of linear and PWM dimming techniques
can be used to achieve a large dimming ratio.
R03
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