AN2435

Practical design example of a sepic converter

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2.7

Selection of other components

Selection of the other components of the circuit may be made using the guidelines for a

boost converter which are given in [2 ]. Capacitor C1 must be considered in parallel with the

input capacitor, which means that a small capacitor of 10 nF is adequate for the current

design.

For the control loop design the procedure used for a boost converter in [4 ] may be followed.

The small signal model developed in this document must be considered.

The charge pump which supplies the IC, while respecting the calculated steady state

values, needs to be a little over-sized. During start-up, capacitor C2 is not pre-charged by

the inrush current as in a boost converter, and therefore, the charge pump provides less

L6562 has to be increased during start up phase to supply the IC, even if the charge pump

is not able to provide enough current.

Figure 11.

Output diode current averaged over the switching cycles

Figure 12.

Transformers with symmetrical structures

Primary Winding

Secondary Winding

Primary Winding

Secondary Winding

a

b