Implementing the TL431 feedbac...

Implementing the TL431 feedback loopImplementing the TL431 feedback loop
Christophe BASSO MOTOROLA SPS, Toulouse Center Avenue Eisenhower, BP1029, 31023 TOULOUSE Cedex France 33 (0)5 61 19 90 12; e-mail: R38010@email.sps.mot.com

This paper details the numerous ways to implement a feedback network with an optocoupler and a TL431 when implementing shunt regulators. Depending on the configuration of the devices and the method used to measure the open-loop response, some unusual results may appear. The shunt regulator The optocoupler is used alone and delivers some current to a shunt regulator such as implemented by the MC3337X series or the MC44608. In these devices, the duty-cycle DC is adjusted by injecting a current into a feedback pin (FB). When the current is low or zero, the duty-cycle is pushed to the max (74% for the M