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Interesting DC-DC converter circuit

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    #1

    Interesting DC-DC converter circuit

    The attached snippet is from a AC Technology Corp M1230B MC Adjustable AC Drive 3 HP low voltage supply. Link voltage is good at 380VDC. The converter won't start. I'm trying to figure out what you would call this topology so I can search for some theory on how it works. I'm guessing that it's some kind of resonant converter but I haven't been able to find anything like it. Seems like there are not enough parts on the primary side...
    Attached Files
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    #2
    Re: Interesting DC-DC converter circuit

    I should also mention that the other side of the opto-isolator is just connected to the DC output on the secondary side.

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      #3
      Re: Interesting DC-DC converter circuit

      A bit more context. Dates at ~1995. I've tested the transistors and diodes in circuit. All seem fine. I've checked the ESR of C103, it's showing .11 (good). D3-D6 are labeled "37JPH-". I haven't been able to figure out what they are, but they all have a forward voltage of 0.52V. Outputs are something like 6V@100ma, +15V@20ma, -15V@10ma so I'm guessing total output is under 1W. One interesting point is that a couple of the SMD components have come loose from the PCB and had to be resoldered, so I touched up all the SMD parts. I know the unit worked as recently as four days ago. I've updated the schematic and attached a top view of the board. There are no components on the bottom side except for the bridge rectifier and intelligent IGBT bridge, both fine.
      Attached Files

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        #4
        Re: Interesting DC-DC converter circuit

        horrible.
        i hate those type of cheap circuits - it reminds me of 2$ usb chargers.

        the lower winding gets powered, the upper winding then energises and cancels the supply to the lower winding.
        atleast it looks that way!

        go watch some "diode gone wild" video's on utube - he does a lot of psu reverse engineering with deep explanations.

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          #5
          Re: Interesting DC-DC converter circuit

          What was the UF value of this capacitor

          This seems a high value for a capacitor but it depends on the UF value

          “ I've checked the ESR of C103, it's showing .11 (good). ”
          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

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            #6
            Re: Interesting DC-DC converter circuit

            @stj: Thanks for the link to "diode gone wild". He provides the name of the topology (self oscillating flyback converter) and a good explanation for how it should work.

            @sam: I've checked C103 again and got the following:
            C103, Spec: 470uF 35V, measured 450uf and ESR .17 ohms (in circuit)

            I'm going to try replacing it since it does seem to be on the borderline.
            Thanks, -Reed

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