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mc33063 buck configuration pull down resistor

david sabalesky0
Intellectual 275 points


What value should the pull down resistor be when using the MC33063 in buck mode with external npn transistor?

Should you use a current limiting resistor to the base of the external npn transistor? Buck Mode

  • 0
    TI__Guru**** 166606 points

    David,

    Figure 9a in data sheet should have the external resistor between NPN base and emitter (not ground) and should be about 100 ohms to help turn off the transistor quickly. (new data sheet coming soon corrects error in drawing)

    The base current limits itself to (emitter current) / (beta +1) so no series resistance is needed.