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  1. #1
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    LT3750 Capacitor Charging Problem

    Hey Guys,

    I am new to this forum. I just wanted some help regarding the Lt3750 chip. I have read the previous threads on the same.. I didn't want to reply on that since it is too old. I have designed my PCB for charging a 470uF 400V Cap with a 6A configuration 300V circuit configuration. I have followed the recommended design for the PCB and also the components I am using are as recommended in the datasheet. The capacitor is not getting charged though. It only charged once. None of the components have been damaged. I also connected the charge and done pin with arduino and on triggering the charge pin,done pin goes low immediately and on giving LOW to charge Pin the Done goes HIGH immediately. The capacitor is not getting charged though. Please someone help me on what are the first steps of debugging I should consider.

    Thanks!

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  2. #2
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    Re: LT3750 Capacitor Charging Problem

    Although you say otherwise, it sure SOUNDS like you've got a damaged component. According to the data sheet:

    DONE (Pin 2): Open Collector Indication Pin. When target output voltage is reached, an NPN transistor turns on. Requires a pull-up resistor or current source. Any fault conditions such as thermal shutdown or undervoltagelockout will also turn on the NPN.

    So, maybe you've got some other issue.

    I would take an oscilloscope and look at the the MOSFET gate and drain, the voltage on the RBG pin, etc.



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  3. #3
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    Re: LT3750 Capacitor Charging Problem

    Make sure that you have connected the transformer with the correct polarity of the windings.
    The output should go negative when the MOSFET is switched on, and the capacitor is charged via the diode when the MOSFET is switched off.



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  4. #4
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    Re: LT3750 Capacitor Charging Problem

    Thanks for the reply.Yeah I think you are right. The switching of the transistor might be because of thermal shutdown. I don't have an oscilloscope with me for now.. I am arranging for that. One thing I wanted to confirm is the transformer connection. I have uploaded the pic of my schematic.. please have a look and let me know if the connections are right. The transformer I am using is DA2032-ald and I have also uploaded a pic of transformer pins.
    Click image for larger version. 

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