AN2754

Buck topology switching power supply

9/20

reduce the ripple current on the LEDs branch. To calculate the ripple current that flows

through the LEDs it is necessary to estimate the impedances of the branches of both the

LED and output capacitor (Zo, Zc). In this procedure let us suppose that the triangular shape

of the ripple current on the inductor is approximately sinusoidal.

Figure 8.

Output impedence

Equation 15

Equation 16

The following equation can be used to estimate the impedance of the output capacitor which

guarantees the desired ripple current on the LEDs for a given inductor ripple current:

Equation 17

RFB

rD

+

=

Cout

Fsw

2

1

ESR

⋅

⋅

π

⋅

+

=

O

LED

L

LED

C

Z

i

i

i

Z

×

∆

−

∆

∆

=