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AC-DC rectifier 5V, 2A learning and testing

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    #1

    AC-DC rectifier 5V, 2A learning and testing

    Hello guys,
    I have a TV box power supply adapter, 5V, 2A that's not working correctly. Input is AC 230V 50 Hz.
    I would like to use this as a learning example.
    First of all, when adapter is connected to AC power, there is 5 V DC at its output (4.95V) when no load is connected.
    If a small light bulb is connected (5V, 0.3A), the output voltage drops to 0.85V and there is a weak light on the bulb.

    Attached is a picture of PCB. There are two black IC s on the board. The smaller one 4 legs is probably a voltage feedback chip. On it is written something like: PC817C 1452, and I cannot see that anything is written on larger 8 legs chip.

    So when load is connected voltage drops and even green LED light becomes weak. Even after I remove the adapter from the AC power, its DC output remains 0.85V for a long time.

    What could be the problem in such cases, i.e. when there is output voltage with no load connected?

    Thank you.
    Attached Files
    Tags: None
    #2
    Re: AC-DC rectifier 5V, 2A learning and testing

    Can you please show the back side of this board thanks
    9 PC LCD Monitor
    6 LCD Flat Screen TV
    30 Desk Top Switching Power Supply
    10 Battery Charger Switching Power Supply for Power Tool
    6 18v Lithium Battery Power Boards for Tool Battery Packs
    1 XBox 360 Switching Power Supply and M Board
    25 Servo Drives 220/460 3 Phase
    6 De-soldering Station Switching Power Supply 1 Power Supply
    1 Dell Mother Board
    15 Computer Power Supply
    1 HP Printer Supply & Control Board * lighting finished it *


    These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

    1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
    2 Hem Saw Computer Stack Board

    All of these had CAPs POOF
    All of the mosfet that are taken out by bad caps

    Comment

      #3
      Re: AC-DC rectifier 5V, 2A learning and testing

      Usually these capacitors are the problem, especially at the power output.
      Attached Files

      Comment

        #4
        Re: AC-DC rectifier 5V, 2A learning and testing

        Originally posted by Adenitz View Post
        Hello guys,
        On it is written something like: PC817C 1452
        Thank you.

        Here is the data sheet for the part that you were asking about

        https://cdn.badcaps-static.com/pdfs/...34e9701c06.pdf

        The 8 pin ic chip is probably some type of switching transformer power supply regulator
        Last edited by sam_sam_sam; 10-11-2022, 11:36 AM.
        9 PC LCD Monitor
        6 LCD Flat Screen TV
        30 Desk Top Switching Power Supply
        10 Battery Charger Switching Power Supply for Power Tool
        6 18v Lithium Battery Power Boards for Tool Battery Packs
        1 XBox 360 Switching Power Supply and M Board
        25 Servo Drives 220/460 3 Phase
        6 De-soldering Station Switching Power Supply 1 Power Supply
        1 Dell Mother Board
        15 Computer Power Supply
        1 HP Printer Supply & Control Board * lighting finished it *


        These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

        1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
        2 Hem Saw Computer Stack Board

        All of these had CAPs POOF
        All of the mosfet that are taken out by bad caps

        Comment

          #5
          Re: AC-DC rectifier 5V, 2A learning and testing

          Hello and thank you all for your replies.
          The backside of PCB is given in the attached picture.
          The caps don't show and visual signs of wearing (bumps).
          One capacitor is 400V , while other two are 47 uF 50V and 470 uF 25V.

          Should I try to replace the caps?

          What could be a reason for voltage drop if bulb is connected, 7V, 0.3A should not be a large load for 5V 2A power supply, right?
          Attached Files

          Comment

            #6
            Re: AC-DC rectifier 5V, 2A learning and testing

            Capacitors do not always show a malfunction if the cover is swollen, some of which have rubber squeezed out on the back side, where the conclusions are, the ESR increases (the main reason), but because of them it happens mainly that it does not hold the load, try changing that which is 12v output. (470x25)

            Comment

              #7
              Re: AC-DC rectifier 5V, 2A learning and testing

              I had a (new) 5V 2A PSU that was very weak, it could not supply even 0.5A without sagging voltage and it was a bad IC, the DIP-8.

              Comment

                #8
                Re: AC-DC rectifier 5V, 2A learning and testing

                thats clearly a USB psu, i seriously doubt it is designed for more than 1A

                Comment

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