Secondary feedback configuration example

VIPer53 - E

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Since the dynamic characteristics of the converter are set on the secondary side through

components associated to U3, the compensation network has only a role of gain

stabilization for the optocoupler, and its value can be freely chosen. R5 can be set to a fixed

value of 1k

Ω, offering the possibility of using C7 as a soft start capacitor: When starting up

the converter, the VIPer53 device delivers a constant current of 0.6 mA on the COMP pin,

creating a constant voltage of 0.6V in R5 and a rising slope across C7. This voltage shape,

together with the operating range of 0.5V to 4.5V provides a soft start-up of the converter.

The rising speed of the output voltage can be set through the value of C7. The C4 and C6

values must be adjusted accordingly in order to ensure a correct start-up.