UC2845L-Q1: Flyback design

Hi Wenjie,

Yes, UC3845 belongs to the same family. So for the first 2 questions, please use the same WEBENCH with UC3845 for your application, and let us know if you have further questions.

wenjie Yang said:

3. Does UC2845L-Q1 has the design reference doc?

By reference document, do you mean like a EVM reference? If so, unfortunately, no, we do not have an EVM for UC2845L-Q1.

wenjie Yang said:

4. In my applicaiton, shall I remove the primary aux winding, only using Input battery for VCC?

Yes, you can bias the IC externally.

wenjie Yang said:

5. What's the design purpose of RZ/DZ/Q1 and R21/D21/C21 in the attached UC3845 WB design file?

RZ/DZ/Q1 is the over-voltage protection clamp circuit. It is a zener clamp circuit with a transistor buffer to handle high current.

R21/D21/C21 are used for compensation.

Thank you.

Best,

Adhvaidh

Hi, Wenjie,

The schematics looks good in theory. But it is difficult to judge the two feedback loops how they can work. It looks the higher regulated output voltage takes control. In flyback the two outputs are cross regulated  through transformer windings coupling so difficult to use feedback loop to regulate the other one. In your design, 170V 100W will dominate and 12V 1W will be largely depending on 170W and 100W load condition. You can try your idea. But from our experience 12V 1W loop does not seem useful.  

Hi Wenjie,

We really appreciate your patience. The circuit looks good after the changes were made.

Best,

Adhvaidh