Linear regulators are simple in concept. Figure 1 shows a typical linear regulator design that uses a closed-loop control scheme. The pass transistor provides regulation by acting as a variable resistor that limits the current flowing from input to output. As a result, the output voltage must always be lower than the input voltage.
The advantages and disadvantages of switching regulators versus linear regulators for DC/DC conversion
Dec 13, 2024
Regulating DC voltages has a long history: the first integrated circuit regulators date back fifty years. Linear regulators came first and some of the earliest designs are still in use today. The demand for increased efficiency and design flexibility later spurred the development of switching regulator topologies. Both linear and switching designs have advantages and disadvantages in particular applications: this blog will compare and contrast both approaches.
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The resistor divider chain R1/R2 is chosen so that at the required output voltage VOUT, the divided-down voltage at the error amplifier inverting input is the same as the VREF voltage at the non-inverting input. The error amplifier controls its output in such a way that the voltage difference between its inputs is always zero.
Linear regulators produce minimal switching noise, making them suitable for applications requiring low noise levels. In normal operation, even if the input voltage fluctuates rapidly, the output voltage remains stable. This means they can also very effectively filter out input ripple, not only at the fundamental frequency, but also as far as the fifth or tenth harmonic. The limitation is only the bandwidth of the internal error amplifier. Low-noise application examples include data acquisition systems, precision analog circuits, and internet of things (IoT) sensors.
Linear regulators are also cost-effective and have fewer components, making them suitable for low-cost or space-constrained consumer and industrial designs. On the other hand, the voltage between input and output, (VIN – VOUT), appears across the pass transistor, resulting in a power loss that must be dissipated as heat. The loss can be a substantial proportion of the supplied power depending on the voltage difference between input and output. For example, a linear regulator that produces a 5V output from a 9V input wastes 44% of the supplied power as heat for an efficiency of only 56%. Due to heat dissipation requirements, linear regulators may require larger heatsinks or additional cooling mechanisms.
Linear regulators produce minimal switching noise, making them suitable for applications requiring low noise levels. In normal operation, even if the input voltage fluctuates rapidly, the output voltage remains stable. This means they can also very effectively filter out input ripple, not only at the fundamental frequency, but also as far as the fifth or tenth harmonic. The limitation is only the bandwidth of the internal error amplifier. Low-noise application examples include data acquisition systems, precision analog circuits, and internet of things (IoT) sensors.
Linear regulators are also cost-effective and have fewer components, making them suitable for low-cost or space-constrained consumer and industrial designs. On the other hand, the voltage between input and output, (VIN – VOUT), appears across the pass transistor, resulting in a power loss that must be dissipated as heat. The loss can be a substantial proportion of the supplied power depending on the voltage difference between input and output. For example, a linear regulator that produces a 5V output from a 9V input wastes 44% of the supplied power as heat for an efficiency of only 56%. Due to heat dissipation requirements, linear regulators may require larger heatsinks or additional cooling mechanisms.
Switching regulators trade efficiency for complexity
The invention of the switching DC/DC converter provided increased efficiency but required a more complex design methodology. In contrast to linear designs, switching converters exploit the energy-storing properties of inductive and capacitive components to transfer power in discrete energy packets. The packets of energy are stored either in the magnetic field of an inductor or in the electric field of a capacitor. The switching controller ensures that only the energy required by the load is transferred in each packet, so this topology is very efficient. The best designs can achieve efficiencies of 95% or greater. Unlike a linear regulator, the efficiency of a switching regulator is not dependent on the voltage between input and output.
Figure 2 shows the simplified block diagram of a switching DC/DC converter. Numerous types of switching topologies exist, offering great design flexibility. A switching regulator can produce an output that is either higher or lower than the input (step up or step down) or invert the voltage from input to output. There are both isolated and non-isolated topologies.
Switching regulators can be more compact due to their improved efficiency and reduced need for heat dissipation. However, they are more difficult to design and implement, requiring a variety of skills including digital and analog control, magnetics, and board layout. For a given power level, increasing the efficiency of a design typically requires greater complexity with additional components and increased cost.
The rapid switching action can introduce electromagnetic interference (EMI) or switching noise, which may affect nearby components. The designer must pay attention to component placement, grounding, and trace routing to minimize the effects of switching noise. Switching regulators are preferred for any application where high efficiency is critical, including high power supplies for servers, computers, and industrial process control. Applications that are battery-powered also benefit from higher efficiency, which translates into increased battery life. Examples include portable equipment and electric vehicles. Due to their efficient operation, switching regulators often eliminate the need for bulky heatsinks. This is especially beneficial in space-constrained designs.
Switching regulators can be more compact due to their improved efficiency and reduced need for heat dissipation. However, they are more difficult to design and implement, requiring a variety of skills including digital and analog control, magnetics, and board layout. For a given power level, increasing the efficiency of a design typically requires greater complexity with additional components and increased cost.
The rapid switching action can introduce electromagnetic interference (EMI) or switching noise, which may affect nearby components. The designer must pay attention to component placement, grounding, and trace routing to minimize the effects of switching noise. Switching regulators are preferred for any application where high efficiency is critical, including high power supplies for servers, computers, and industrial process control. Applications that are battery-powered also benefit from higher efficiency, which translates into increased battery life. Examples include portable equipment and electric vehicles. Due to their efficient operation, switching regulators often eliminate the need for bulky heatsinks. This is especially beneficial in space-constrained designs.
RECOM’s Regulator
RECOM engineers are skilled at designing the best combination of switching and linear topologies for specific applications.
In higher power designs, the primary conversion is typically done with switching regulators to maximize overall efficiency. The switching stages produce a variety of voltages that may supply loads directly, or a linear regulator can be added in series for those use cases where low noise is required. In low-power applications the best strategy depends on the application. A simple linear regulator may be all that is required.
In some cases, a combination of switching and linear designs can yield the best result. Figure 3 achieves a regulated output by adding a linear regulator in series with the +Vout line on the secondary side of an isolated switching topology – in this case a push-pull converter. This approach packages both regulators in a single device, achieves higher efficiency than a pure linear design, and is employed in some of RECOM’s lowest wattage DC/DC converters.
In some cases, a combination of switching and linear designs can yield the best result. Figure 3 achieves a regulated output by adding a linear regulator in series with the +Vout line on the secondary side of an isolated switching topology – in this case a push-pull converter. This approach packages both regulators in a single device, achieves higher efficiency than a pure linear design, and is employed in some of RECOM’s lowest wattage DC/DC converters.
Conclusion
Switching regulators feature high efficiency, great design flexibility, and smaller form factors, but their designs are more complex and switching noise may cause EMI issues. Linear regulators feature simplicity, low noise, and cost-effectiveness, but are less efficient and can require bulky heatsinks. RECOM can help you pick the right combination of features for all types of power conversion applications.
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