LED2000 datasheet(15/40 Pages) STMICROELECTRONICS

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DocID023432 Rev 4

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LED2000

Application notes

The embedded compensation network is RC = 70 K, CC = 195 pF while CP and CO can be

considered as negligible. The error amplifier output resistance is 240 M



so the relevant

singularities are:

Equation 12

6.4

LED small signal model

Once the system reaches the working condition, the LEDs composing the row are biased

and their equivalent circuit can be considered as a resistor for frequencies << 1 MHz.

The LED manufacturer typically provides the equivalent dynamic resistance of the LED

biased at different DC currents. This parameter is required to study the behavior of the

system in the small signal analysis.

For instance, the equivalent dynamic resistance of the Luxeon III Star from Lumiled

measured with different biasing current level is reported below:

Equation 13

If the LED datasheet does not report the equivalent resistor value, it can be simply derived

as the tangent to the diode I-V characteristic in the present working point (see Figure 7).

11 6 kHz



fP LF

34 Hz



rLED

1,3



ILED 350mA

0,9



ILED 700mA







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