MLX10803_06 Datasheet, PDF (20/25 Pages) List of Unclassifed Manufacturers – High power LED driver

IC specification MLX10803
High power LED driver
7.3. Switching frequency considerations and constant light output
As already shown, the switching frequency depends on the peak current as well as on the monoflop time for a given
coil. Furthermore it depends on the coil inductance itself.
Due to the principle of switch mode power supplies, the current through the LED is kept constant for any
supply change. The parameter that changes in order to keep the current constant is the switching
frequency itself. The lower the supply voltage, the lower the switching frequency. Furthermore, the supply
current is affected by supply changes: with an increasing supply voltage the average supply current decreases.
The graph below shows the normalised luminous flux versus the power supply for a standard application with one
white Luxeon III LED driven at 750mA. The parameters are optimised for the 24V board net.
The luminous flux at 24V has been set to 100%. The graph indicates that the light output is minimally dependent on
supply changes over the whole range from 16 to 32V.
120.00
115.00
110.00
105.00
100.00
95.00
90.00
85.00
80.00
16
MLX10803
Normalized luminous flux Θv/Θv(24V) vs. supply voltage
Θv/Θv(24V)=f(VBAT)
Iled=750mA, fsw=70kHz (@24V)
18
20
22
24
26
28
30
32
VBAT [V]
3901010803
Rev 024
Page 20/25
Data Sheet
7/DEC/06