Hi guys, I want to understand the concepts behind switching power supplies and have done a bit of reading. I would like to show a schematic that I have drawn up and explain my thinking with the purpose of getting some general constructive feed back on my grasp of the concept.
As far as my understanding goes, energy is stored within the inductor and the voltage drop across the inductor depends on its charge state. If it was a simple RL circuit then the voltage drop would change as a function of time. The switching of the supply is what keeps the voltage drop across the inductor at equilibrium. The diode acts to keep the circuit when the switching transistor is off, so the diode needs to be very fast acting and a schotkky diode is chosen due to this speed requirement.
In my schematic, the switching is controlled with a comparator and a reference voltage. If the voltage across the load is below the reference voltage, then the supply is switched on. When the voltage drop exceeds the reference, the supply switches off and the load is powered only by the energy stored within the inductor. This switching keeps going back and forth as the load discharges the inductor. Switching speed in this instance is dependant on the load, but I understand well designed units would have a fixed switching rate with a dynamic duty cycles, and a microcontroller could be used here to manage this.
I have used a PNP BJT as a high side switch, whereas supplies that handle more current would likely use P channel mosfets.