COMPENSATING DIGITAL PWM CONTROL LOOPS

摘要

Digital pulse width modulators (PWM) are emerging in commercially viablepower supply control Ics. Although digital PWMs provide many benefits in terms offlexibility and power system management, they also present some challenges to powersupply designers not familiar with digital signal processing (DSP) techniques. Thisdifficulty is evident when compensating the power supply control loop. This paper willshow the parallels between the analog control loop and the digital control loop. It will beshown that each block in a digital control loop can be represented by a continuous “s”domain transfer function, and thus can be modeled or simulated with commonly availableprograms such as MathCAD. Using a minimum of DSP theory, equations are derivedwhich allow the designer to calculate digital filter settings (coefficients) with a calculator.The paper will show a worked example with test results from a power supply controlledby a digital PWM.