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    #61
    Re: A question about PWM IC's

    Originally posted by R_J View Post
    Just a note on the source resistor, it should be a non-inductive type once you do the final repair. Also without a load on the power supply, the circuit may start but be in burst mode until a load is placed on the secondary. This is a complex, green mode ic, and the circuit operates at high frequency. The whole circuit is fairly simple as the ic does a lot of the work, I suspect and hope the ic should fix the smps.
    Originally posted by R_J View Post
    Just a note on the source resistor, it should be a non-inductive type once you do the final repair. Also without a load on the power supply, the circuit may start but be in burst mode until a load is placed on the secondary. This is a complex, green mode ic, and the circuit operates at high frequency
    Nice one for the heads-up on those points.

    I was unware on 'non-conductive' resistors, so that is for sure good to know.

    There are three different ones here, two are wire-wound, one a fat, green 5W affair and the other looking like a wire-wound carbon.
    The third is a square-edged, white ceramic axial, 2W

    Looking into it, some non-inductive resistors have an extra yellow band, which none of these have. I'll see if I can't get back to the shops today.

    Comment


      #62
      Re: A question about PWM IC's

      Originally posted by keeney123 View Post
      As a last thing I can point you to in understanding this circuit and others is this site.

      https://training.ti.com/pulse-width-...pwm-converters

      I find the free ti training course offer a good fundamental understanding.

      Cool.

      Thank you for your patience.

      Comment


        #63
        Re: A question about PWM IC's

        Originally posted by keeney123 View Post
        As a last thing I can point you to in understanding this circuit and others is this site.

        https://training.ti.com/pulse-width-...pwm-converters

        I find the free ti training course offer a good fundamental understanding.
        Thanks for posting this website link for this type of information
        Very informative information
        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


          #64
          Re: A question about PWM IC's

          Originally posted by sam_sam_sam View Post
          Thanks for posting this website link for this type of information
          Very informative information
          I once took an amplifier source from them for free. At the time they actually gave you a test and they graded it. So, your welcome.

          Comment


            #65
            Re: A question about PWM IC's

            Originally posted by Crystaleyes View Post
            Nice one for the heads-up on those points.

            I was unware on 'non-conductive' resistors, so that is for sure good to know.

            There are three different ones here, two are wire-wound, one a fat, green 5W affair and the other looking like a wire-wound carbon.
            The third is a square-edged, white ceramic axial, 2W

            Looking into it, some non-inductive resistors have an extra yellow band, which none of these have. I'll see if I can't get back to the shops today.
            Most non-inductive resistors have a black band as the last band

            In this case I would just use a metal oxide type resistor, like a MOSX2CT52RR12J 0.12Ω/2watt from digikey
            Attached Files
            Last edited by R_J; 04-24-2022, 02:52 PM.

            Comment


              #66
              Re: A question about PWM IC's

              Originally posted by R_J View Post
              Most non-inductive resistors have a black band as the last band

              In this case I would just use a metal oxide type resistor, like a MOSX2CT52RR12J 0.12Ω/2watt from digikey
              The shops were all shut on saturday due to Carnival, but are you saying that this will cause the unit to fail?
              Digikey is a long way from here and the 40 USD postage is too much, so it'll have to be something else, at least for now, until I get back to Europe.

              The new chip is installed, and only the source resistor remains.

              Can the PSU not be switched on for a short period of time, just to verify, or is it absolutely critical to use non-inductive resistors on the source of the switching Mosfets?

              Comment


                #67
                Re: A question about PWM IC's

                Any resistor should be ok for the source resistor, being such a low value I doubt there would much inductance in even a wire wound resistor. So you should be ok.
                The part number I gave was from digikey KOA Speer electronics, but any supplier should be able to provide a suitable resistor

                Comment


                  #68
                  Re: A question about PWM IC's

                  Originally posted by Crystaleyes View Post
                  The shops were all shut on saturday due to Carnival, but are you saying that this will cause the unit to fail?
                  Digikey is a long way from here and the 40 USD postage is too much, so it'll have to be something else, at least for now, until I get back to Europe.

                  The new chip is installed, and only the source resistor remains.

                  Can the PSU not be switched on for a short period of time, just to verify, or is it absolutely critical to use non-inductive resistors on the source of the switching Mosfets?
                  So here is an insight to wire wound resistors.

                  https://eepower.com/resistor-guide/r...und-resistor/#

                  Comment


                    #69
                    Re: A question about PWM IC's

                    A quick update.

                    I replaced the Ic and used a 0.12 ohm ceramic resistor and switched it on.

                    No 24V DC output and no frequency on the gate pin of the IC.

                    Unfortunately I had been using hooks to measure the FET voltages and even though it was switched off, I hadn't waited for the filter caps to discharge before removing them which shorted it out, so until I get a replacement FET there is not a lot else to report.

                    All invaluable lessons, although I am now short of ideas on resolving this.

                    This PSU is not really so important, so I may just take the experience learnt and move on, if a replacement FET does nothing new.

                    Comment


                      #70
                      Re: A question about PWM IC's

                      Originally posted by keeney123 View Post
                      So here is an insight to wire wound resistors.

                      https://eepower.com/resistor-guide/r...und-resistor/#
                      Thanks.

                      Classic quote from the first page seems to sum up my situation perfectly


                      “The way to succeed is to double your failure rate.”

                      - Thomas J. Watson

                      Comment


                        #71
                        Re: A question about PWM IC's

                        Originally posted by Crystaleyes View Post
                        Thanks.

                        Classic quote from the first page seems to sum up my situation perfectly


                        “The way to succeed is to double your failure rate.”

                        - Thomas J. Watson
                        One of my teachers once quoted Thomas Edison on inventing something new. "It's 1% genius and 99% persistence."
                        Edison tried thousands of experiments to come up with the light bulb. He categorized everything he did. One of those things was the foundation for a vacuum tube.
                        My teacher was one of the people who made the first transistor computer that Westinghouse paid $2 million to develop.

                        Comment

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