VOLTAGE REGULATORS The working principles of voltage regulators
A voltage regulator is a circuit that creates and maintains a fixed output voltage regardless of how the input voltage and load conditions change, keeping power supplies in a range compatible with other components.
A voltage regulator is a very simple device with a feed-forward design that makes use of negative feedback control loops. When a steady and reliable voltage is needed, the voltage regulator is the device of choice. It’s used to generate a fixed output voltage that stays constant despite changes in both input voltage and load conditions. By doing this, it protects other components from damage that could be caused by voltage spikes.
There are two main types of voltage regulator: linear and switching, each with their own sub-types. These are used in a variety of applications.
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Linear voltage regulators
There are two types of linear voltage regulator: series and shunt. Linear regulators act as voltage dividers. The resistance of the voltage regulator changes with the load, resulting in a constant output voltage.
A linear voltage regulator uses an active pass device such as a MOSFET or BJT which is controlled by a high-gain operational amplifier. To maintain a constant output voltage, linear regulators adjust the pass device resistance by comparing internal voltage to the sampled output voltage and then driving the error to zero.
While linear voltage regulators have fast response times to load or line changes, low electromagnetic interference, low noise, and produce a low output ripple voltage, they’re relatively inefficient, take up a large amount of space, and require the use of a heatsink. Furthermore, voltage above the input cannot be increased.
To operate, linear voltage regulators only need an input and output capacitor. This makes them simple, reliable, and highly cost-effective for design engineers to use.
Linear regulators are often found in applications that are cost- and noise-sensitive, low-current, or constrained by space. Examples include consumer electronics and Internet of Things devices which can’t accommodate bulky packages.
Switching voltage regulators
In contrast, switching voltage regulators are typically more complicated and require selecting external component values, tuning control loops, and more careful designs and circuit layouts.
Switching regulators can be both step-down and step-up converters or a combination of both. This makes them far more versatile than linear regulators and makes them inherently useful to a wider variety of applications.
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Switching voltage regulators are highly efficient, offer better thermal performance, and can support a higher current. Depending on the application requirements, switching regulators can achieve efficiency levels of up to 95 percent. Unlike linear regulators, however, switching regulators may require additional external components such as inductors or feedback resistors, making them more challenging from a design perspective and generally more expensive to integrate.
Switching regulators are often found in applications where efficiency and performance drive design. Examples include industrial, enterprise, and automotive applications.
Voltage regulator limitations
One of the biggest drawbacks of linear regulators is that they can be inefficient due to large levels of power dissipation in certain applications. A linear regulator’s voltage drop is comparable to that across a resistor, making them better for applications that have lower VIN/VOUT differentials.
When considering a linear regulator, it’s important for design engineers to forecast power dissipation so as to avoid instances of overheating and component damage. It’s also important to keep in mind that linear regulators are only capable of step-down conversion.
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While switching regulators are highly efficient, this makes them less cost-effective than linear regulators. This is because they’re larger, more complex, and can create more noise if the wrong external components are used, which themselves lead to a larger bill of materials. Noise is an important consideration for any given application because this can negatively impact circuit operation and performance.