1. In the previous lab, you found that the controller would need a phase boost near 1 kHz, which will now be termed the cross-over frequency fc. At this frequency, the buck converter's transfer function had a gain near 25.3 dB and a phase of approximately -141 degrees. Assume that the controller should provide a phase margin of 60° at fc, that the feedback sensor has a gain of kFB = 0.2 and the PWM chip uses a peak ramp voltage of 1.8V. Following the steps outlined in section 4.4 of the Mohan textbook, calculate the following variables, which in turn will help you determine the controller's transfer function:
a) φ boost
b) Kboost
c) fz
d) ωz
e) fp
f) ωp
g) kc
2. Write down the equation for the voltage-mode controller's transfer function, GC(S), with all variables except ‘s' now replaced with numerical values.
3. Given R1 = 100 kΩ, calculate the values of the other components in the op-amp circuit that will be used to implement the voltage-mode controller:
a) C2
b) C1
c) R2
d) R3
e) C3