• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 869 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

About the function of TL2842B.

masahiro nasu
Prodigy 30 points
Other Parts Discussed in Thread: TL2842B

Hello!

I use the TL2842B with the fly-back circuit.
The composition of the current detection circuit is equal to Fig-2 in the TL2842B datasheet.
The VFB-pin is connected to GND.
The COMP-pin connects the phototransistor through the 100Ω.
(The emitter of the phototransistor is connected to GND.)

An intermittent oscillation has been generated at a light load.
However, when the 100Ω is connected between Rf/Cf and ISENS-pin of Fig-2,intermittent oscillation is improved.

Can you explain this phenomenon?
I was not able to do.
And,is this good method?

Could you please help me?

Best regards.
Masahiro

  • 0
    TI__Guru**** 164976 points

    Hello Masahiro,

    When you say "the" 100 ohm resistor, did you move the 100 ohm to pin 2 (Isense) and now have no resistor (0 ohms) between pin 1 (comp) and the phototransistor?

    That change probably did not change the phase margin of the control loop much; you are likely just marginally stable at this point.

    I suggest changing the frequency compensation of the output side of the optocoupler.

    Regards,
    Ron M.

     

     

  • 0 in reply to Ron Michallick
    Prodigy 30 points

    Hello! Ron,

    100 ohms are connected with both COMP and ISENS.
    Could you see the following connection diagrams?


    I'm sorry in longhand.

    How do you think by seeing this connection diagram?

    I want to know the reason that an intermittent oscillation improved.

    Best regards.
    Masahiro

     

  • 0 in reply to masahiro nasu
    TI__Guru**** 164976 points

    The resistor will drop a voltage proportional to the input bias current, but this will be less than 1mV.

    I do not understand how that insignificant shift in operating point would prevent an oscillation.

    Regards,
    Ron M.

     

  • 0 in reply to Ron Michallick
    Prodigy 30 points

    Hello! Ron,

    Thank you for your comment.
    I'm sorry for troubling your hand.

    Best regards.
    Masahiro