If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

# UCC28810: Doubt regrading a reference design - Application note SLUA 752

Part Number: UCC28810

Greetings of the day, I am George, a novice player in power electronics, currently learning about led drivers and circuits. While referring UCC28810's Application note SLUA752(70W Streetlight driver)

I have some doubt about a portion of circuits, I would like to know what is the function of those particular arrangement of components.

1. R21A , R21B ( 1 M ohm) L2,L3 (100uH)  I would like to know why a filter circuit after the Bridge ? What is function of that?

2. D9A(1N4007), R38A(1M ohm) along with C19A, C20A(10uf,450V). Here I would like to know why the diode and resistor connected in parallel and the capacitor in series instead of using one 407uF 300/450V

I would be grateful if anyone could explain me with the reason behind of using and also the functionality of the circuit

Regards

George Thomas

• Hello George,

1 This is the EMI filter
R21A,B dampen out any high frequency oscillations caused by high frequency ringing of L2,3 with C6A and provide attenuation at high frequency

2  The caps C19A,C20A are in series so that together they have a continuous  voltage rating of 630V.
The diode charges the caps fast and the resistor provides a slow discharge.
This is important because directly connecting the caps to the line will give you a poor power factor.
The purpose of the caps is only to absorb any high voltage line transient energy due to lightening or ESD transient

Regards

John  I

• Hello John Sir,

Thank you for the reply, Second one I understood clearly,

About the EMI filter after the bridge circuit! , I have another doubt,

I saw many other design with Inductor -resisitor in parallel only on the  positive + line. Is that does the same job?  is it mandatory to put EMI filter on both lines after bridge.?

I like to learn more about CMC &  Differential mode choke design for AC to DC converter especially for LED driver from 30W - 110W , if you could help me with relevant lead I would be happy.

Kind Regards

George Thomas

• George,

Normally the EMI filter is placed directly on the AC line , after the fuse and before the filter.
On low power designs a simple choke is sufficient to meet EMI requirements and this is placed after the bridge because the RMS current is smaller here.
The subject of EMI is discussed extensively in the TI power seminars and these are located here:

Regards

John

• Hello John Sir,

Thank you for the information, I will look into the seminar.

Have a great day!

Regards

George Thomas