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AN2129 APPLICATION NOTE

Figure 7. Dimming network with zero dimming voltage (maximum current)

Eq 1

The second limit state is depicted in Figure 8. In this case the current through the Rsense is

zero (LED is off) and thus on point A there is a zero voltage (i.e. ground). The Equation 2

shows the calculation for this state.

Figure 8. Dimming network with maximum dimming voltage (zero output current)

Eq 2

100mV

R5 R6 I

⋅⋅

⋅

R4 R5

⋅

R4 R6

⋅

R5 R6

⋅

++

---------------------------------------------------------------------------

=

100mV

V

dimMAX

R4 R5

⋅

R4 R5

⋅

R4 R6

⋅

R5 R6

⋅

++

---------------------------------------------------------------------------

=