UC3845: Inquire about the impact of UC3845's flyback switching power supply, RCD absorption circuit of MOS transistor on EMC, and how to calculate the RCD value? What is the function of the capacitor between pin 3 and pin 4?

liujun

Part Number: UC3845

Tool/software:

How to calculate the value of C11 in Figure 1 when using UC3845 as a flyback switching power supply? What is the function of C11?
In addition, what are the effects of R, C, and D on EMC in Q1's RCD absorption circuit?

thank you!

Figure 1

11 months ago

0 Hong Huang 11 months ago

TI__Guru 74115 points

Where did you got this circuit? In typical applications, C11 does not exist. You need to talk to the circuit designer to find out.

Your cited circuit does not show R C D around Q1, so you need to label where these are.

0 liujun 11 months ago in reply to Hong Huang

Intellectual 310 points

What are the effects of resistors, capacitors, and diodes on EMC in RCD (R1, C7, D1) circuits?

Figure 2

How to optimize and improve EMC of flyback switching power supply?

Thank you

0 Ning Tan 11 months ago in reply to liujun

TI__Genius 12795 points

Liujun,

There are many tutorials online to explain the RCD impact on EMC. Here are few examples.

https://www.youtube.com/watch?v=KHw9IueFcwA

https://www.youtube.com/watch?v=FXpsAsVJFVc

EMC optimization is a big topic and it is beyond the scope of this forum as well.

0 liujun 11 months ago in reply to Ning Tan

Intellectual 310 points

Thank you

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UC3845: Inquire about the impact of UC3845's flyback switching power supply, RCD absorption circuit of MOS transistor on EMC, and how to calculate the RCD value? What is the function of the capacitor between pin 3 and pin 4?