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Power & Energy
Forum Why is my LTC3780 only giving 0.8V - 2.8V output?
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  • lct3780
Related

Why is my LTC3780 only giving 0.8V - 2.8V output?

tim687
tim687 over 8 years ago

Recently I bought two of these, I was needed to remove all of the pots since they where bad. I soldered a resistor (500K) like this to the board to make sure that the undervoltage protection won't go off, since that was the issue I had when I powered up the board for the first time. That issue caused the fault led to light up and the output to not work.

I got one board working, since I wanted to get one working before I changed the other one. I am not sure if the resistor fix is correct here.

image

 

Now, a few days (maybe weeks further), I continued with the project and tried a reverse polarity protection circuit. That didn't work very well, but it was fun to see something, that is not supposed to light up, light up (@28.5V). Everything continued to work after the short!


The next day I soldered the banana plugs that came in to the output wires and all of a sudden the device wouldn't power more than around 2.8V. The fault led is lighting up and the chip is getting very hot.

 

Did I blew up the chip by testing out the lighting effects on components?

 

The strange thing is that, the other board isn't working at all. Same problem as the first one.

I didn't test the shortcut capabilities of the second board though.

 

I have ordered two new LTC3780's and a few of the LM358N's to make sure that they are all good.

 

 

I am doing anything wrong?

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  • michaelkellett
    0 michaelkellett over 8 years ago in reply to tim687

    Some designs have  a resistor between Vin and pin 21 which would explain why the voltage is dropping at that point and your power supply is still alive.

     

    If you take the 3780 off you can test the MOSFETS from its pads without taking the heatsink off.

     

    Put a 100R resistor between that 600W supply and the board while you are testing them.

     

    MK

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  • tim687
    0 tim687 over 8 years ago in reply to michaelkellett

    How do I test the mosfets exactly?

     

    The 100R resistor is preventing huge current flows I suppose?

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  • tim687
    0 tim687 over 8 years ago

    According to a website I found online regarding mosfet testing, the mosfet should be dead. I'll send both boards back to banggood and hope to get decent quality boards back.

     

    Thanks for your help!

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  • michaelkellett
    0 michaelkellett over 8 years ago in reply to tim687

    Good luck.

    What country are you in ?

    MK

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  • tim687
    0 tim687 over 8 years ago in reply to michaelkellett

    The Netherlands

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  • michaelkellett
    0 michaelkellett over 8 years ago in reply to tim687

    If you had been in the UK I could have sent you the board we bought from Amazon - but it's a bit pricey to send it to the Netherlands.

     

    Actually you might not want it since we took the heatsink off and added some wires !

     

    It looks very like yours - we were not impressed with it's stability (it would produce quite large amplitudes of low frequency noise at some load/output settings).

     

    MK

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