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UC2842A: can i use this controller for flyback converter for 450V DC output?

sharathkumar jidigam99
Prodigy 110 points
Part Number: UC2842A
Other Parts Discussed in Thread: UC2844A

Hi

i am using UC2842A i.e 100% duty cycle controller for my flyback converter power output is 160W,output voltage is 450V, input is 90-264 VAc can i use this controller for this application?

presently i am testing with this controller facing problem like PWM,out put voltage is oscillating when it is coming to loop,and getting full voltage at 130Vac input with 65% load but not at 90V ac

transformer is ETD34, 35 Primary,80 Secondary turns.

same power tested with UC2844A Facing same problem that getting full 450V Out put at 140-150V ac input but not oscillating with full load with same transformer and other transformer i.e 92 secondary turns 35 primary turns. To resolve the issue of getting full out put voltage in universal input voltage changed the controller to 2842 but facing same problem with one added problem 

please help me in this regards.

  • 0
    TI__Genius 9130 points

    Sharathkumar,
    Thanks for your interest in TI here. This sounds like a very tough spec for a Flyback, regardless of the chosen controller. Why are you using a Flyback at 160 W?

    Can you provide as much detail as possible about the spec and requirements?  
    We can then see if there is any existing TI Design with a similar spec that can be reommended.

    Thanks,
    Bernard

  • 0 in reply to Bernard Keogh
    Prodigy 110 points

    Hi Bernard,

    Thanks for reply

    Spec

    input 90-264V Ac, 

    out put

    Voltage 450V DC

    Current 350mA but continuous 300 to 320ma  load is available.

    initially i tried with UC2844A with input bridge rectifier in doubler mode i.e selection switch for 110/230 operation this flyback is worked fine, then changed to normal rectifier mode facing problem at full load notable to deliver the power at input 90VAC.

  • 0 in reply to sharathkumar jidigam99
    TI__Genius 9130 points
    Sharathkumar,

    Can you post you schematic and values? Particularly transformer magnetising inductances and Rcs values.

    How much capacitance is after the bridge rectifier?

    It sounds like you may not have enough capacitance after the diode bridge in standard non-doubler mode, so the Flyback stage cannot cope with the minimum ripple point.

    Or it may be that the power stage design just cannot cope with the low line operation, regardless of the low-freq ripple.

    Even going to higher Dmax controller may not help if the Flyback stage is not properly designed.


    Some other questions

    - if the doubler scheme works, why change?

    - why use a Flyback stage instead of a boost stage (would even get PFC with a boost)?


    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    Prodigy 110 points

    Magnetizing inductance is 170uH,Rcs =0.75 connected 3 nos parallel,

    Capacitance after the bridge rectifier is 560uF,i connected other values parallel to this  but not  getting output voltage at 90VAC

    PFC is not used because we need a isolation between input and output.

    actually one more converter is running on the board so we changed from doubler mode to rectifier mode.

  • 0 in reply to sharathkumar jidigam99
    TI__Genius 9130 points
    Sharathkumar,

    Can you post better quality copies of the schematics? I cannot read the images you posted.

    Can you also include transformer details - magnetising inductance, turns ratios, core size, turns counts?


    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    Prodigy 110 points

    HCLAMP_450VSUPPLY.pdf

    Transformer details 

    ETD34 Primary 35 turns secondary each section 40 turns and Auxiliary 3 Turns, Magnetizing Inductance 170uH

    another transformer ETD34 Primary 35Turns,Secondary each section 46 turns (92turns) ,Auxiliary 4 turns,Magnetizing Inductance 170uH

  • 0 in reply to sharathkumar jidigam99
    TI__Genius 9130 points
    Sharathkumar,

    I see from your schematic that the transformer aux winding polarity is backwards. This means that the bias rail is proportional to Vin rather than Vout, and may be the reason that you are having trouble operating at lower input voltage.

    I would recommend that you double check the transformer and schematic aux winding polarity to verify.


    Thanks,
    Bernard
  • 0 in reply to Bernard Keogh
    Prodigy 110 points
    transformer polarity is correct only but mentioned wrong in schematic i.e (dot end is 5 in auxiliary winding),i given bias voltage from external supply the behavior was same.