+ Post New Thread
Results 1 to 10 of 10
  1. #1
    Full Member level 5
    Points: 1,571, Level: 9

    Join Date
    Jul 2015
    Location
    Faridabad India
    Posts
    242
    Helped
    21 / 21
    Points
    1,571
    Level
    9

    SMPS circuit fault analizing help

    Hello,

    i want some help regarding to SMPS circuit fault correction. In the PCB circuit i found the driver mosfet ic is damaged (locking physically). I want to know, what other components (like any diode) can be damaged as per this situation.

    Circuit diagram

    untitled2.png

    Thanks in advance.

    •   Alt30th November 2016, 11:25

      advertising

        
       

  2. #2
    Full Member level 4
    Points: 1,753, Level: 9

    Join Date
    Sep 2013
    Posts
    207
    Helped
    72 / 72
    Points
    1,753
    Level
    9

    Re: SMPS circuit fault analizing help

    VIPER 20 is an integrated fly back switch, this IC may burn due to its internal circuit problems so no other external components will effect. If the IC is burn badly then surrounding components may distort. For a complete troubleshooting, First check BR1 Bridge rectifier,if BR1 is ok then check D3 and ISO1
    No other components failure


    1 members found this post helpful.

  3. #3
    Super Moderator
    Points: 21,730, Level: 35
    andre_teprom's Avatar
    Join Date
    Nov 2006
    Location
    Rio de Janeiro, Brazil
    Posts
    6,655
    Helped
    809 / 809
    Points
    21,730
    Level
    35
    Blog Entries
    5

    Re: SMPS circuit fault analizing help

    Although the silicon components are generally more prone to burn, and the electrolytic capacitors are also affected in the event of any overvoltage, I would not rule out the possibility that the transformer if it is not burned, that at least had its properties changed, In the case of overheating of the insulation varnish of the windings; Just a guess.
    --------------------------------------------------------------------------------------------------
    Part of the world that you live in, You are the part that you're giving ( Renaissance )



  4. #4
    Full Member level 5
    Points: 1,571, Level: 9

    Join Date
    Jul 2015
    Location
    Faridabad India
    Posts
    242
    Helped
    21 / 21
    Points
    1,571
    Level
    9

    Re: SMPS circuit fault analizing help

    Thank you very much

    I will try according your instruction and will reoprt.


    Although the silicon components are generally more prone to burn, and the electrolytic capacitors are also affected in the event of any overvoltage, I would not rule out the possibility that the transformer if it is not burned, that at least had its properties changed, In the case of overheating of the insulation varnish of the windings; Just a guess.
    Yes you can be right.



    •   Alt30th November 2016, 12:09

      advertising

        
       

  5. #5
    Full Member level 5
    Points: 1,571, Level: 9

    Join Date
    Jul 2015
    Location
    Faridabad India
    Posts
    242
    Helped
    21 / 21
    Points
    1,571
    Level
    9

    Re: SMPS circuit fault analizing help

    Hi,

    I checked pcb circuit and found a zener diode (do not have any value on it) is connected on opto 817B collector and emitter pin (see attached picture). I checked it with multimeter and found it resistance was 25E in both condition (probe changed).

    IC Viper53 datasheet says

    COMP pin
    "Input of the current mode structure, and output of the internal error amplifier. Allows
    the setting of thedynamic characteristic of the converter through an external passive
    network. The useful voltage range extends from 0.5V to 4.5V. The Power MOSFET is
    always off below 0.5V, and the overload protection is triggered if the voltage exceeds
    4.35V. This action is delayed by the timing capacitor connected to the TOVL pin."

    and

    "The VIPer53 device delivers a constant current of 0.6 mA on the COMP pin,
    creating a constant voltage of 0.6V in R5 and a rising slope across C7. This voltage shape,
    together with the operating range of 0.5V to 4.5V provides a soft start-up of the converter."

    My question is, what is the value of zener diode?
    Is it damaged?


    smps-circuit.png
    Last edited by Ranbeer Singh; 6th December 2016 at 05:26.



  6. #6
    Full Member level 4
    Points: 1,753, Level: 9

    Join Date
    Sep 2013
    Posts
    207
    Helped
    72 / 72
    Points
    1,753
    Level
    9

    Re: SMPS circuit fault analizing help

    Hi,

    Schematic symbol is not look like Zener; any way I believe your word.

    If the Zener diode reads low resistances in both directions, this is a sign that the diode is shorted. A diode should not measure low resistance in the reverse biased direction. Defected diode will cause the compensation pin voltage always less than 0.5V, so the mosfet will remain off state
    Over voltage protection will work if the voltage on the com pin exceeds 4.35V. So the Zener voltage will fall between 9V to 15V



  7. #7
    Full Member level 5
    Points: 1,571, Level: 9

    Join Date
    Jul 2015
    Location
    Faridabad India
    Posts
    242
    Helped
    21 / 21
    Points
    1,571
    Level
    9

    Re: SMPS circuit fault analizing help

    So the Zener voltage will fall between 9V to 15V
    I am not understanding, if 4.35v is comp pin threshold limit voltage. It's means if limit crosses, over voltage condition will occur and mosfet will be off. I mean the voltage never will above 4.35. So how will we need a much voltage zener diode.



  8. #8
    Full Member level 4
    Points: 1,753, Level: 9

    Join Date
    Sep 2013
    Posts
    207
    Helped
    72 / 72
    Points
    1,753
    Level
    9

    Re: SMPS circuit fault analizing help

    Data sheet says
    Input of the current mode struct
    ure, and output of the intern
    al error amplifier. Allows
    the setting of thedynamic c
    haracteristic of the converter through an external passive
    network. The useful voltage range extends fr
    om 0.5V to 4.5V. The Power MOSFET is
    always off below 0.5V, and the overload prot
    ection is triggered if the voltage exceeds
    4.35V. This action is delayed by the
    timing capacitor connected tothe TOVL pin.

    It means if the voltage exceed 4.35V(Due to overload) then only overload protection will work by varying the pulse sequence. If you put 4.35V Zener at that place over load protection should not work

    Hope it is clear



    •   Alt6th December 2016, 12:21

      advertising

        
       

  9. #9
    Full Member level 5
    Points: 1,571, Level: 9

    Join Date
    Jul 2015
    Location
    Faridabad India
    Posts
    242
    Helped
    21 / 21
    Points
    1,571
    Level
    9

    Re: SMPS circuit fault analizing help

    Yes

    What will be sutable value? 9v zener?



  10. #10
    Full Member level 4
    Points: 1,753, Level: 9

    Join Date
    Sep 2013
    Posts
    207
    Helped
    72 / 72
    Points
    1,753
    Level
    9

    Re: SMPS circuit fault analizing help

    Better try and see the result


    1 members found this post helpful.

+ Post New Thread
Please login
--[[ ]]--