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measured LED driver
Rd --- Resistance of LED driver, can be calculated by V-I curve
Rd Coefficient = Rd / (Vo / Io)
Vf——LED Positive conduction bias, can be calculated from the Rd, please find the
specific example as follows.
Rf ——resistivity of the working point, can be calculated from the Rd
LED is equivalent to the resistor Rd and the power source Vf in series. Its I-V curve is
equivalent to the tangent of the true LED nonlinear VI curve at the operating point (Vo,
Io),as shown in Figure 3.24:
Vo = Vf + Io×Rd;--------------------- formula 3.1
Let Vf = a×Vo; (a<1)
Vo = a×Vo + Io×Rd;
Rd = (1 − a) ×
Vo
Io
Let coeff = Rf = 1-a
That is
Rd = Rf ×
Vo
Io
a = 1 − Rd ×
Io
Vo
;--------------------- formula 3.2
By checking LED specification to know Vo, Io, and Rd, a can be calculated by formula 3.2;
Rf = 1 − a = Rd ×
Io
Vo
;----------------- formula 3.3
Figure 3.25 LED Mode setting Page
ET System electronic GmbH
