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UC3843A: Voltage Mode

John Lee11
Prodigy 100 points
Part Number: UC3843A
Other Parts Discussed in Thread: UC1843

I want to configure my UC1843 to run as voltage mode.  Figure 23 of the data sheet gives an example but I do not know how to calculate the resistors. 

www.ti.com/.../uc1843.pdf

  • 0
    TI__Guru 66135 points
    Hello John,

    I am not sure why the data sheet is showing extra circuitry that is not required to get the device to operate in voltage mode control. It might be to get a more linear PWM ramp.

    A simpler way to do this would be to use the circuitry presented in figure 21. The only difference is that you would not need RCS, you would just short RCS to ground. The oscillator has a 1.7V peak amplitude the voltage on the other side of the NPN transistor on figure 21 would be 1.1 to 1.0V. If you used 2K ohm resistors for Rram and Rcsf the circuit would provide a 500 to 550 mV PWM ramp and would operate in voltage mode control.

    Regards,

    Mike