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UC3843A maximum duty vs Rt

George Chen
Intellectual 2175 points

Hi Team,

Is there any guarantee range for this maximum duty vs Rt figure?

For example, is Rt is set as 3.1kohm, the maximum duty should be 85% from the figure of datasheet page7.

And what is the range? 80~90%?

Or is there any formula with relationship to this figure?

Thanks.

  • 0
    TI__Genius 15910 points

    Unfortunately, back when this device was developed, it was common to empirically derive the curves.  The maximum duty cycle limit is set by the ratio of the external oscillating charge resistor , RT, and the internal oscillator discharge transistor on-resistance, with some impact from the parasitic capacitance of the package and bond wires.  There isn't an equation that calculates the duty cycle with any guarentee of precision.