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Buck Boost with 555

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by polashd, Nov 27, 2016.

  1. int main(){return 0;}

    int main(){return 0;} New Member

    Oct 10, 2017
    Noo Joizee
    Before spicing the booster I'm working on (with a 555 oscillator) I wanted to spice the simplest possible SMPS booster I could find: http://soundation.blogspot.com/2012/07/very-simple-5v-to-65v-dc-boost.html

    I replaced the MOSFET with the MPSA42 I'm using, and the circuit seems to work in spice, switching at about 40 kHz and with an open-circuit output voltage a bit above 80 V. I'd like to breadboard it and need advice on a suitable PNP to use. Here's a plot of the voltages seen by the PNP:
    Node 2 is the emitter, 1 is base and 5 is collector. Those Vbe spikes up to the full output voltage look a bit worrisome. Would a suitable high-voltage PNP BJT tolerate them?

    Edit: this circuit has awful efficiency and is of no practical interest. Sorry for the noise.
    Last edited: Dec 3, 2017
  2. dr pepper

    dr pepper Well-Known Member Most Helpful Member

    Oct 6, 2008
    North west UK
    An mpsa92 is a complement for the mpsa42.

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