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Why is D5 failing?

inavitech

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Project I am working on. I'm not a board designer. Box integration is more my thing. This circuit is needed for providing a 13VDC output. Input power is 28VDC. When 28VDC is applied the power supply voltmeter drops to 6VDC, and it goes into current limiting mode. Current output is maxed out at 5 amps. D5 starts to look like a well done hotdog on the grill and begins to smoke. There were other parts of this circuit in the original design that are not being utilized, but as I said I'm not a board guy. I think with the removal of the unnecessary portion, the current is too high, thus R15's value is too low now. Figured maybe one of you on the forum might have the answer. So how this works is the tester utilizes 28VDC to test a battery pack. All of the other functions work properly when removing this part of the circuit from the equation. There is a test for a particular circuit in the battery that requires 13VDC to verify proper operation, so I can't ditch this portion of the tester. Maybe there is a better way to do this?

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  • 0

    if you supply an external  13v to the output of this how much current is required to run the rest of it ? 

    is this a commercial machine with a brand and model ?

    do you have the original circuit diagram or have you just traced this out. ?

    is there a shunt resister ( for current sence ) after Q1 ? 

    which the op amp is connected to.

    You said there are unnecessary portion, i think you need to draw more of circuit

    if this machine is for testing batteries  could this be part of a current dump to control the discharge of the battery

      

Reply
  • 0

    if you supply an external  13v to the output of this how much current is required to run the rest of it ? 

    is this a commercial machine with a brand and model ?

    do you have the original circuit diagram or have you just traced this out. ?

    is there a shunt resister ( for current sence ) after Q1 ? 

    which the op amp is connected to.

    You said there are unnecessary portion, i think you need to draw more of circuit

    if this machine is for testing batteries  could this be part of a current dump to control the discharge of the battery

      

Children
  • 0 in reply to acdc90

    The 13VDC is just a pass through in the battery pack to test a diode. If the circuit path is good the annunciator LED on the test box will be lit dim since it is receiving 50% power. Then the next step is to throw another switch that adds 24VDC from the battery to the line internal to the battery giving the output about 32VDC, so the annunciator should be on brightly. That is all it is for. Just to test a pass through circuit in the battery with a diode. The diode is there to prevent back flow of current when the battery has output on the pass through so it flows the correct direction.