Buck Converter Design Demystified
Buck-Converter Design Demystified
Stepdown (buck) switching converters are integral to modern electronics. They can convert a voltage source (typically 8 V to 25 V) into a lower regulated voltage (typically 0.5 V to 5 V). Stepdown converters transfer small packets of energy using a switch, a diode, an inductor and several capacitors. Though substantially larger and noisier than their linear-regulator counterparts, buck converters offer higher efficiency in most cases. Despite their widespread use, buck-converter designs can pose challenges to both novice and intermediate power-supply designers because almost all of the rules of thumb and some of the calculations governing their design are hard to find. And though some of the calculations are readily available in IC data sheets, even these calculations are occasionally reprinted with errors. In this article, all of the design information required to design a buck converter is conveniently collected in one place. Buck-converter manufacturers often specify a typical application circuit to help engineers quickly design a working prototype, which in turn often specifies component values and part numbers. What they rarely provide is a detailed description of how the components are selected. Suppose a customer uses the exact circuit provided. When a critical component becomes obsolete or a cheaper substitute is needed, the customer is usually without a method for selecting an equivalent component. This article covers only one stepdown regulator topology — one with a fixed switching frequency, pulse width modulation (PWM) and operation in the continuous-current mode (CCM). The principles discussed can be applied to other topologies, but the equations do not apply directly to other topologies. To highlight the intricacies of stepdown converter design, we present an example that includes a detailed analysis for calculating the various component values. Four design parameters are required: input-voltage range, regulated
Stepdown (buck) switching converters are integral to modern electronics. They can convert a voltage source (typically 8 V to 25 V) into a lower regulated voltage (typically 0.5 V to 5 V). Stepdown converters transfer small packets of energy using a switch, a diode, an inductor and several capacitors. Though substantially larger and noisier than their linear-regulator counterparts, buck converters offer higher efficiency in most cases. Despite their widespread use, buck-converter designs can pose challenges to both novice and intermediate power-supply designers because almost all of the rules of thumb and some of the calculations governing their design are hard to find. And though some of the calculations are readily available in IC data sheets, even these calculations are occasionally reprinted with errors. In this article, all of the design information required to design a buck converter is conveniently collected in one place. Buck-converter manufacturers often specify a typical application circuit to help engineers quickly design a working prototype, which in turn often specifies component values and part numbers. What they rarely provide is a detailed description of how the components are selected. Suppose a customer uses the exact circuit provided. When a critical component becomes obsolete or a cheaper substitute is needed, the customer is usually without a method for selecting an equivalent component. This article covers only one stepdown regulator topology — one with a fixed switching frequency, pulse width modulation (PWM) and operation in the continuous-current mode (CCM). The principles discussed can be applied to other topologies, but the equations do not apply directly to other topologies. To highlight the intricacies of stepdown converter design, we present an example that includes a detailed analysis for calculating the various component values. Four design parameters are required: input-voltage range, regulated