FB pin LNK-PH series

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             I made a circuit using lnk419, 24V 2A. The over-voltage circuit similar to Figure 7 of the data sheet, but the output current was always low, even changing the value of the feedback resisitor.

            So I pulled out the circuit transistor Q3 and the current output improved, ie increased. Then I cut the rest of the track circuit board approximately 10mm and current output came in 2A. The sensitivity of this pin is very high! Now the circuit is functioning well, and I made over voltage protection controlled by BP pin.

            BUT now, I need PWM dimming using FB pin...  Dimerization through the FB pin is really possible? The components associated to do dimerization via this pin will not to "load" this pin ??  just 10mm of pcb track was terrible to me.  

Regarding noise sensitivity of the trace, please follow the layout guidelines in LinkSwitch-PH datasheet. Many design examples and actual designs that have been done with LinkSwitch-PH and the it certainly does not need 10mm clearance. Please review your layout and make sure that there is no high-current switching trace like drain trace close to FB pin.

 

As for pwm dimming, you can refer to DER-263 or check out this forum thread since there are various types of pwm dimming.

 

http://www.powerint.com/forum/power-supply-design/can-i-perform-pwm-dimming-using-linkswitch-ph