Current Limit Reduction with Line Voltage

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For a design using TOPSWITCH-JX, what is the appropriate calculation for the resistance connecting from line DC voltage to pin X? I need to limit the power output with varying line input.

You have to choose the resistor based on the Fig 36 in data sheet page 31. Select X pin ressitor based on your target and Fig 37 first, and then calculate the resistor which connected between Line and X pin. As can be seen from Fig36, the current limit is kind of linear with X pin current.




I understand how to select the external current limiting via Figure 37. What is the equation or formula to calculate the resistor between Line and X pin to limit the power output?

Sorry,  we can not provide you with the equation to calculate that.


Is there a reason why Power Integrations can not provide a method of calculating the resistor value between Line and X pin? How does PI Expert and PIXls Designer calculate this value? I'm asking this because there are conflicting results between the two programs. If I spend some time analyzing this circuit I can get to the equation(s) to calculate this value but it's discouraging to use a part where the manufacturer does not give full support!