08-09-2017, 09:14 AM
The control schemes of type 1, 2 and 3 are characterized by having 1, 2 and 3 poles respectively in the compensation response. This document provides mathematical formulas, resulting bode plots, and real-world implementation for these control schemes using standard op-amp voltage feedback amplifiers. Most modern PWM ICs have the built-in error amplifier but, for clarity, the error amplifier is shown here as a stand-alone component. The op-amp is supposed to be ideal. All mathematical expressions here include a minus sign at the start that refers to the 'subtraction' part of the feedback loop when the output voltage is compared to the reference. The actual offset bode plots ignore this minus sign to give the conventional responses of the transfer function.