Instructional buck converter

This is a non-isolated, unregulated, continuous conduction mode (CCM) buck converter with 1.1V output into a 1kOhm load. It operates at 100kHz and 50% duty cycle Wait for the circuit to reach steady-state, then note how the average current through the capacitor is 0, yet the average current through the inductor is positive – AKA "continuous". There is (ideally) no current through the MOSFET when the gate is at 0V, so this means the current must be sourced from the diode during this off period. Inspect the (free-wheeling) diode to confirm. Play with the period (inverse of frequency) and duty cycle (pulse width) of the oscillator to change the output voltage. Change the resistance of the load resistor to see the effect on its supply voltage and stability. This circuit lacks input/output regulation. Start the circuit from 0s and note the power-on conditions as the circuit starts; both output voltage and current overshoot specifications as the capacitor charges (inrush current). Note how the MOSFET operates in the linear region. This generates heat, thereby reducing efficiency. Also notice the (downward) spike in reverse current when the diode's bias reverses (increase frequency to exacerbated the effect). This is diode's charge transferring from one side of the P-N junction to the other (reverse recovery). The high currents generated from this recovery also reduces efficiency.

published 9 years ago