Solution Finder Get Tech Support

Feedback Gain for Adjustable Outputs

Posted by: aliaykan on

Hi,

 

How can I set feedback opto gain for adjustable outputs? Instead of directly connect the gain resistor to output, fixing the gain resistor's voltage via zener is useful like attachment?

 

Requirements:

3-25V / 10A output by Flyback

3-25V / 18A output by LLC

Files

Attachment Size
Fixed Bias.jpg 169.49 KB

Comments

Submitted by PI-Tucker on 10/01/2014

Yes it's a good idea but you may need to add a phase lead network, a series RC, from the output to the top of the opto LED.  

Also 3 V is pretty low; you'll have to use either a TLV431 (1.25V), or have a separate winding from the transformer. For the flyback, a "forward" winding. Its voltage will vary less than 3-25V.  For the LLC, a winding wound on the primary.

 

Also, note that an LLC running from 3-25V output voltage will have issues with making the feedback loop fast and stable across the wide ratio of input to output votlage as Vo goes from 3-25V.  It helps to always make it run above resonance. However efficiency won't be so good.