www.delorie.com/electronics/spice-stuff/   search  
Spice/GNUCap Projects

Buck Regulator

This circuit is a simplified buck regulator. Instead of a digital logic block controlling the regulator, a simple triangle wave and comparator generates the switch pulses. Commands to run:
gnetlist -v -g spice-sdb -obuck.net buck.sch
ngspice
    source buck.net
    tran 0.001us 0.25ms
    plot nout ndiode nin Vind#branch Vcap#branch

gnucap notes

gnucap
    get buck.net
    print tran v(*) i(*)
    tran 0.25ms 0.25ms trace all >z
    !gwave z &
then drag the signals you want onto the gwave canvas.

Things to try

The buck-math script generates ideal values for the inductor and capacitor based on the load and vin/vout parameters. What happens is you use a smaller inductor? A smaller capacitor?

The inductor value is a minimum. Try one ten times bigger. Add a PWL/switch/resistor to the load to simulate a step load. What happens to the load response time?

The current through the inductor falls nearly to zero, or even hits zero depending on the vin/vout ratio. What can you do to keep it from falling to zero?

What changes if you change the frequency? What doesn't change?


  webmaster   donations   bookstore     delorie software   privacy  
  Copyright 2011   by DJ Delorie     Updated Dec 2011