TOP264EG Dual output cross regulation improvement.

Posted by: Brosnan Gomes on 11/08/2018

Hi,
I have designed a circuit using PI expert suite for 40V, 0.5A and 5V, 0.5A dual output with the 5V output being regulated through an opto coupler.

The circuit at no load on both outputs gives the required voltages with the 5V being better regulated with no fluctuations.
But as I load the 40v rail without loading the 5v one, the 40v output fails to supply the required current and the voltage drops to around 17V.
Next I loaded the 5V output keeping the 40v one open and found the 5v one could supply the required current. So I went ahead loading the 40v one too and noticed that it was now supplying the required current.
Is there a way to make the 40V supply the required current while the feedback loop is on the 5v supply?

Is there a way to regulated both the outputs simultaneously? Anyways I want the 40v one to be a tighter regulated output.
Have attached the design pdf for reference.

Please suggest the methods I should be looking at to improve the cross regulation.

Thanks
Brosnan

Files

Design_for_dual_output.pdf (2.43 MB)

Comments

Hi Brosnan,
I have created a sample computation that you can use for iterations in your circuit. You will need additional resistor to have weighted feedback. (Please refer to attached file)
Regards,
Jedidiah

Attachment	Size
Weighted_Feedback.PNG (95.17 KB)	95.17 KB

Hi Jedidiah,

Thanks for replying,
So we just need to add a 4.8M ohms feedback from the 40v side?

Regards
Brosnan

Regards,
Brosnan

Hi Brosnan,
Sorry, I got mistake in the computations. Change R10 to 2.22 Mohms, R12 to 74kohms, and R11 to 4.83kohms.
Regards,
Jedidiah

Attachment	Size
Weighted_Feedback_revised.PNG (72.15 KB)	72.15 KB