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Original question:

TL2844: Frequency Calculation Question

TL2844: application problem.

Reed
Expert 1620 points
Part Number:

1. What is the role of Qsc? Can it be removed?

2. Can WE replace Q1, DZ and RZ with resistors?

3. For the resistance and capacity of the generated reference design, we will select similar values from the existing material library. After modification, is there any software that can simulate whether the loop composed of TL431 and photocoupler is stable?

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    TI__Mastermind 27795 points

    Hi,

    1. What is the role of Qsc? Can it be removed?
      1. The NPN is a buffer between the RT, CT (Ramp) and the ISENSE. A portion of the Ramp is being added to the ISENSE signal and this is the slope compensation necessary to assure control stability when using peak current mode control at/near 50% duty cycle. If using peak current mode control, do  not remove these components. Here is a E2E thread discussing the "how to" of slope compensation.
    2. Can WE replace Q1, DZ and RZ with resistors?
      1. The three components are forming a series pass regulator necessary to provide a regulated secondary-side bias voltage for the optocoupler. Leave these components as they are, otherwise, if VOUT is dropping and the bias voltage for the4 opto will also be dropping and the gain could drastically decrease.
    3. For the resistance and capacity of the generated reference design, we will select similar values from the existing material library. After modification, is there any software that can simulate whether the loop composed of TL431 and photocoupler is stable?
      1. Please download and experiment with TI Power Stage Designer. After you enter you chosen topology and define your design parameters, you will see a "Loop Calculator" tool tab that can be used to model the control loop.

    Thanks for connecting through E2E.

    Regards,

    Steve M