Most electronic systems rely on voltage regulators to provide stable direct current (DC) levels. This article explains how voltage regulators work and reviews the two main types of regulators used for DC-DC conversion: switching regulators and linear regulators. Common applications for each are highlighted by comparing their benefits and limitations.
Regulating and Improving DC Voltage Levels
Electronic systems require specific DC levels to operate safely and efficiently. A rectifier converts alternating current (AC) from the main supply to DC. A DC-DC converter (Figure 1) then optimizes this output, eliminating fluctuations and providing a precise target DC voltage. These converters also adjust the voltage from sources such as solar panels, battery packs, and vehicle alternators to align with predetermined voltage parameters.
Figure 1. Standard DC-DC converter.
Linear and switching regulators help to implement DC-DC conversions for a variety of functions, such as buck, boost, and lift. Linear regulators provide a simple but limited method of achieving small voltage reductions to provide a stable output with minimal noise. These regulators do not support step-up or step-down configurations because of their lower efficiency, inherent voltage drop, and current output limitations. In contrast, switching regulators offer greater flexibility and higher efficiency, adapting to isolated and non-isolated DC to DC conversions in a variety of topologies ranging from significant voltage drop to boost and lift.
Switching Regulators
Switching regulators use power switches, inductors, and diodes to transfer energy from input to output and regulate voltage. They achieve voltage regulation through the fast switching of power switches, which are typically field-effect transistors (FETs) and managed by switching controller integrated circuits (ICs). A key method of regulating these FETs involves pulse width modulation (PWM), where the duration of the “on” state is adjusted to regulate the amount of energy transferred to the load.
Figure 2. Simplified schematic of a switching regulator circuit, highlighting the PWM logic and FET drivers. (Image credit: Renesas)
In a feedback control loop, these ICs, along with resistors, capacitors, and voltage/current sensors, continuously adjust the switching state and PWM duty cycle to ensure a stable and accurate voltage output.
The switching regulators can place the FETs as discrete components external to the controller or integrate them into the same IC (Figure 2). The latter configuration broadens the applicability to a variety of devices and functions, such as buck and boost converters, inverters, and flyback transformers. IC integration also simplifies design, enabling compact form factors while improving performance and efficiency.
Switching regulators typically achieve efficiencies over 90% by using transistors as switches (fully on or off). This configuration reduces the voltage drop across the switch (when it is on) and limits the current (when it is off), effectively minimizing power losses. In addition, the switching regulator significantly reduces thermal dissipation, resulting in a low input-output voltage differential and medium load current.
Linear Regulators
Linear regulators (Figure 3) use transistors in the input DC path to precisely regulate voltage and current. A feedback loop controls the on-state of the transistors, effectively stabilizing the output voltage even when the input voltage or load changes.
Figure 3. Basic schematic of a linear regulator circuit showing key components and current management. (Image credit: Analog Devices)
However, linear regulators incur power losses because the transistors dissipate energy in the form of heat when bridging input and output voltage gaps. The inefficiency is most noticeable in high-power applications, such as powering a 5 V, 10 A load from a 10 VDC supply, which results in 50W losses and 50% conversion. To operate efficiently, the input voltage must exceed the output voltage by a minimum difference called the dropout voltage.
It is important to note that low dropout (LDO) linear regulators can improve efficiency with minimal difference between the input and output voltages. LDOs use a feedback mechanism to adjust their internal resistance to precisely control the output voltage, ensuring minimal dropout even when the supply voltage slightly exceeds the output voltage. LDOs are well-suited for applications that require stable regulation and closely matched voltage levels.
Advantages and Limitations of Switching Regulators
Versatile, high-efficiency switching regulators accommodate isolated and non-isolated DC-DC conversions from significant buck to boost and buck-boost, including flyback, forward converter configurations, and single-ended primary inductor converters (SEPICs). Effectively reducing power loss and heat dissipation, switching regulators utilize low quiescent current (IQ) to maintain no-load operation. Switching regulators are implemented in integrated solutions (FETs directly inside the IC) or modular designs using external power MOSFETs.
Smartphones, smartwatches, and other advanced wearable devices rely on switching regulators to extend battery life through optimized power management, low IQ, and precise voltage regulation. Switching regulators play an equally important role in solar inverters and battery management systems (BMS) that require efficient voltage conversion. In addition, switching regulators in automotive DC to DC converters stabilizes the voltage in advanced vehicle systems, compensating for fluctuations and ensuring consistent power flow. In industrial automation, switching regulators provide reliable, accurate voltage levels for advanced sensors and controllers.
Despite their versatility and efficiency, switching regulators are not typically used for sensitive analog circuits or audio applications that require ultra-low noise and ripple. This is because the switching action typically introduces electrical noise and affects performance. Linear regulators have minimal electrical noise and are considered more suitable for these use cases.
Why Use Linear Regulators?
Linear regulators provide a simple, cost-effective solution for achieving small voltage drops with minimal efficiency losses. They effectively dissipate excess voltage as heat, requiring only basic connections such as input voltage (VIN), output voltage (VOUT), feedback (FB), and (optionally) ground (GND).
A large voltage difference between the input and output can significantly increase the power loss of a linear regulator, thus reducing its efficiency. Although LDOs can operate efficiently when the voltage difference between the input and output is very small, they are unable to raise the output voltage above the input or reverse the polarity of the voltage, so they are limited to buck conversion.
Despite their limitations, linear regulators are a popular choice for analog circuits and audio equipment that require low noise, fast transient response, and minimal voltage difference. Simple, cost-effective linear regulators are also targeted at low-power devices that require no external inductors and very low heat, such as basic digital watches, LED drivers, and low-power analog sensor modules for precision measurement and monitoring.
For communication infrastructure and radio equipment, linear regulators ensure minimal power supply noise and low output voltage ripple. In addition, an internal feedback loop helps to respond quickly to changes in load or input voltage without the need for external compensation.
Summary
Switching regulators offer versatility and efficiency for many DC-DC conversion configurations, including buck, boost, and buck-boost. In contrast, low-noise linear regulators provide a more limited solution for smaller voltage drops where efficiency losses are minimal. Linear regulators are a popular choice for analog circuits, LED drivers, and audio or communications equipment. Switching regulators are aimed at a wider range of applications, from complex wearables and automotive systems to industrial automation, solar inverters, and battery management systems.
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