+ Post New Thread
Results 1 to 2 of 2
  1. #1
    Advanced Member level 5
    Points: 32,618, Level: 44
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    6,791
    Helped
    492 / 492
    Points
    32,618
    Level
    44

    Bridge rectifier dissipation in 60W offline flyback

    Hello,

    We have designed a 60W offline 240VAC input Flyback LED driver with PFC.
    We had to use a DBLS209G rectifier bridge because we couldn’t fit anything bigger on the PCB.
    Each of the 4 diodes in the DBLS209G bridge package carries 124mA average , but each carries 341mA RMS.

    In a thermal test, with a thermocouple glued to the case, the DBLS209G case temperature was 102degC. This was with the PCB in its plastic enclosure, which is also inside a metal enclosure….and the external ambient was 22degC. In the real application, the highest external ambient will be 25degC. –But the lamp will be on for 7 hours per night.

    The DBLS209G datasheet says operating temperature can be up to 150degC. However, I cannot believe this gives long life….i remember when I was at Panasonic, the cases of semiconductors was never above 90degC.

    Do you think we are running this diode too hot for long life?

    Incidentally, there would actually be room to have two DBLS209G packages on the PCB, one on the top side, and one directly underneath it……we could then tie the “AC connection points” of each DBLS209G package together, and make up one more_thermally_capable bridge rectifier out of the two DBLS209G packages. Has anyone actually trIed this?.......i saw them doing this kind of thing on a reverse engineered 3Kw Electric car battery charger. The diode voltage increases significantly enough with current to make this work I would have thought?


    DBLS209G rectifier:
    http://www.taiwansemi.com/products/d...SERIES_I15.pdf

    •   AltAdvertisement

        
       

  2. #2
    Super Moderator
    Points: 259,307, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,270
    Helped
    13773 / 13773
    Points
    259,307
    Level
    100

    Re: Bridge rectifier dissipation in 60W offline flyback

    We can guess about 500 mW total bridge rectifier power dissipation, gives not more than 20K delta over internal "ambient" temperature. Means problem isn't the rectifier, it's total circuit power dissipation. Other components must be expected to be exposed to similar temperatures.



--[[ ]]--