Flyback PWM controller maximum allowable VCC voltage?

[treez]

Hello,

We are using L6566B PWM controller for an offline flyback.

L6566B DATASHEET
https://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00167474.pdf

Do you know if the VCC pin voltage is "self limited" by an internal 23V zener?....the datasheet doesn't say.

(we need to know as the vcc pin is supplied by an unregulated bias winding which "wanders" high and low due to poor coupling.)

 

[Anna Conda]

Geez, you are a lazy son of a ...

The data sheet specifies an internal zener 23-27 volts which only operates when the IC is disabled, normally an internal regulator keeps this pin to 23V for currents up to 20mA.
Therefor if you want to power the IC from an aux supply that has more than 20mA capability you need to keep the volts below 22V, ideally 16-18V for startup...

Try reading data sheets..!!!!!!