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Original question:

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

UCC28810: SLUA752 Application Note doubt

Novin George Thomas1
Prodigy 160 points
Part Number: UCC28810

Dear Sir,

         While I was going through the reference design of UCC28810 in  application note SLUA752, I have a doubt regarding the secondary side diode (output diode ) selection.!

 In the application note SLUA752 page 3 , output diode ( D4 ) part number is STTH1008DTI which have the Forward current rating of 10A, there the design is for 70W which 106 VDC and 600mA Current!

1. I would like to know why that much high rated diode is being used there, what are consideration to choose that part number?

2. Can I used some MUR420 or ES3J in parallel instead of that part number?

I would be grateful if you could help me with relevant information and educate me.

Thanks in advance

*

3302.slua752.pdf

  • 0
    TI__Mastermind 34465 points

    Hello Novin,

    This diode was chosen because it has an 800V reverse voltage rating an a less than 75nS reverse recovery time.
    If you do a search on Digikey for example with these parameters you will find the results are very limited.
    Available parts are mostly in a TO220 package and this of course makes for a fairly high current rating because of the heatsinking properties of the TO220 package.
    If you can find a high voltage ultrafast rectifier  with a current rating of a few Amps instead of 10A then you can consider using that part.

    Regards

    John

  • 0 in reply to John Griffin1
    Prodigy 160 points

    Dear John Sir,

        Thank you for the information. Sir while I have gone through many other design files I could see some used MUR460  x 8  or ES3K  x 6 or US3M x 6 in parallel is that a good practice?

    I have gone through the datasheet of ES3k is has reserve recovery voltage rating of 800V!

    Why do we need we need that much if reverse recovery rate for a 106V 600mA output? I would like to learn more about it ?

    I look forward to hearing from you soon

    Thank you

    Regards

    Novin George Thomas

  • 0 in reply to Novin George Thomas1
    TI__Mastermind 34465 points

    Hello Novin,

    You can certainly try this other part and check its behaviour in the circuit.
    It does have a smaller mechanical package and you can expect it get get hotter in the application.
    You will need to calculate or measure the rms output current in your application and check the forward voltage drop of the selected part.
    Reverse recovery times may vary and some parts have soft recovery versus hard recovery.
    Soft recovery parts tend to give lower voltage recovery spikes.
    This is something you can only test for and is not usually found in the data sheets.
    I recommend that you choose some different parts, test, review your results and make an informed decision on the part you finally choose.
    This is how the process is optimized.

    Regards

    John

  • 0 in reply to John Griffin1
    Prodigy 160 points

    Dear John Sir,

                           Thank you for the support, Sir I have another doubt too,

     IN the Application Note Page No:3, D9A, R38A, C19A, C20A what is function of this circuit? What is this does exactly?

  • 0 in reply to Novin George Thomas1
    TI__Mastermind 34465 points

    Hello Novin,

    You are certainly having a lot of doubts about the SLUA752.

    Your last question was answered in part 2  a previous question that you posted

    Regards

    John