Analysis, Simulation And Experimentation Enable Successful Design Of Power Supply Compensation
by Christophe Basso, ON Semiconductor, Toulouse, France, How2Power Today, Jul 15 2020
Focus:
This 19-page article reviews some of the tools currently available to let you calculate
and simulate the control loop of your power supply design as part of the process of
designing a robust compensation network. Article begins by reviewing the importance of the
power stage response and why designers need to determine the control-to-output transfer
function of the power stage to design the compensation network. It explains how the
compensator corrects the response, the three options for implementing the compensator—op
amp, TL431 and OTA—and the three types of compensation. The next part describes three
techniques to obtain the power stage response including SPICE simulation of an average
model, obtaining the control-to-output transfer function from a small-signal model and
fast analytical circuit techniques (FACTs), and using a SIMPLIS (piece-wise linear)
simulation. The next section describes compensation strategies for buck, buck-boost and
boost topologies, providing guidelines for selecting crossover frequency and phase margin.
Finally, a design example is presented, an ac-dc flyback converter, using SIMPLIS to
extract the power stage response, designing a type 2 compensator and then using SIMPLIS to
check crossover frequency, phase margin and transient response. Finally, designers are
advised to verify performance on the bench and to perform Monte Carlo and worst-cases
analyses.
What you’ll learn:
- How to analyze a power supply’s control loop and design a robust compensation network
- How to obtain a power supply’s power stage response using SPICE simulation of average PWM models, a small signal model and circuit analysis, or a SIMPLIS simulation
- How to ensure the stability of a power supply control loop across real world operating conditions
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