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

Novin George Thomas1

Part Number: UCC28810

Dear Sir / Madam,

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

Please find the link below or find the attachment

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

Thanks in Advance

Regards

George Thomas

slua752.pdf

over 4 years ago

0 John Griffin1 over 4 years ago

TI__Mastermind 34465 points

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

0 Novin George Thomas1 over 4 years ago in reply to John Griffin1

Prodigy 160 points

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

0 John Griffin1 over 4 years ago in reply to Novin George Thomas1

TI__Mastermind 34465 points

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:

https://www.ti.com/ww/en/power-training/login.shtml?DCMP=pwr-psds-archive&HQS=pwr-psds-archive-psds

Regards

John

0 Novin George Thomas1 over 4 years ago in reply to John Griffin1

Prodigy 160 points

Hello John Sir,

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

Have a great day!

Regards

George Thomas

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