HV9910 Supertex, HV9910 Datasheet - Page 6

• Manufacturer Part Number: HV9910
• Description: Universal High Brightness LED Driver
• Manufacturer: Supertex

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Figure 1: Typical Application Circuit
Inductor Design
Referring to the Typical Application Circuit below
the value can be calculated from the desired peak-
to-peak LED ripple current in the inductor.
Typically, such ripple current is selected to be 30%
of the nominal LED current. In the example given
here, the nominal current I
The next step is determining the total voltage drop
across the LED string. For example, when the
string consists of 10 High-Brightness LEDs and
each diode has a forward voltage drop of 3.0V at its
nominal current; the total LED voltage V
Knowing
V
be determined, as:
D= V
Then, given the switching frequency, in this
example fosc=50KHz, the required on-time of the
MOSFET transistor can be calculated:
Ton=D/fosc=3.5 microsecond
IN
=120V*1.41=169V, the switching duty ratio can
LEDs
85-135V AC
AC Input
/V
LED(s) – a string of HB LEDs , 16 diodes
the
IN
=30/169=0.177
NTC
250 V
2R
2A,
nominal
0.1µ F,
250 V
BUSH-2820R5B
coilcraft
250 V
1n F,
LED
rectified
0.1µ F,
250 V
250 V
is 350mA.
1n F,
1N4004
1N4004
input voltage
1N4004
1N4004
LEDS
160 V
68µ F,
1N4004
optional for PFC
is 30V.
68µ F,
160 V
1N4004
6
1µF,
10V
The required value of the inductor is given by:
L = (Vin - V
Input Bulk Capacitor
An input filter capacitor should be designed to hold
the rectified AC voltage above twice the LED string
voltage throughout the AC line cycle. Assuming
15% relative voltage ripple across the capacitor, a
simplified formula for the minimum value of the bulk
input capacitor is given by:
Cmin = I
Cmin = 22 µF, a value 22uF/250V can be used.
A passive PFC circuit at the input requires using
two series connected capacitors at the place of
calculated C
should be rated for ½ of the input voltage and have
twice as much capacitance.
Enable
The HV9910 can be turned off by pulling the
PWM_D pin to ground. When disabled, the HV9910
draws quiescent current of less than 1mA.
VDD
PW M_D
LD
LED
HV9910
VIN
LEDs
*V
MIN
LEDs
GATE
) * Ton/(0.3 * I
GND
. Each of these identical capacitors
CS
RT
*0.06/V
BYV26B
280 kΩ
IN
^2
LED
VN2224
0.2 Ω
) = 4.6mH
750µΗ ,
220nF,
400 V
HV9910
LEDs
C110504