Types of Voltage Regulators

An explanation of three different types of voltage regulators

Voltage regulators take an input voltage and create a regulated output voltage at either a fixed or adjustable level. This automatic regulation of the output voltage level is handled differently by various types of voltage regulators.

Types of Voltage Regulators

The most affordable and often the easiest type of voltage regulators to use are linear voltage regulators. Linear regulators are compact and often used in low-voltage, low-power systems. Switching regulators are more efficient than linear voltage regulators, but are harder to work with and are more expensive. Zener diodes are inexpensive and simple to use but are less efficient than linear regulators.

Assortment of voltage regulators
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Linear Regulators

One of the most basic ways to provide a stable voltage for electronics is to use a standard 3-pin linear voltage regulator, such as the LM7805, which provides a 5-volt, 1-amp output with an input voltage at up to 36 volts (depending on the model).

Linear regulators work by adjusting the equivalent series resistance (ESR) of the regulator based on a feedback voltage, essentially becoming a voltage divider circuit. This lets the regulator output a constant voltage regardless of the current load placed on it, up to its current capacity.

One of the big downsides to linear voltage regulators is the large minimum voltage drop, which is 2.0 volts on the standard LM7805 linear voltage regulator. This means that to get the stable 5 volts output, at least a 7-volt input is required. This voltage drop plays a large role in the power dissipated by the linear regulator, which must dissipate at least 2 watts if it delivers a 1-amp load (2-volt voltage drop times 1 amp).

The power dissipation gets worse as the difference between the input and output voltage widens. For example, while a 7-volt source regulated to 5 volts delivering 1 amp dissipates 2 watts through the linear regulator, a 10-volt source regulated to 5 volts delivering the same current dissipates 5 watts, making the regulator only 50% efficient.

Switching Regulators

Linear regulators are great solutions for low-power, low-cost applications where the voltage difference between the input and output is low, and not much power is required. The biggest downside to linear regulators is that these are inefficient, which is where switching regulators come into play.

When high efficiency is needed, or a wide range of input voltage is expected, a switching regulator becomes the best option. Switching voltage regulators have power efficiencies of 85% or better compared to linear voltage regulator efficiencies that are often below 50%.

Switching regulators generally require extra components over linear regulators. The values of the components have more of an effect on the overall performance of switching regulators than linear regulators. There are also design challenges in using switching regulators effectively without compromising the performance of the circuit resulting from the electronic noise that the regulator generates.

Zener Diodes

One of the simplest ways to regulate voltage is with a Zener diode. While linear regulators are usually basic in design, a Zener diode provides adequate voltage regulation in a single component.

Since Zener diodes shunt all extra voltage above its breakdown voltage threshold to ground, it can be used as a simple voltage regulator with the output voltage pulled across the leads of the Zener diode.

However, Zeners often have limited ability to handle power, which limits these to low-power applications only. When using Zener diodes in this manner, it's best to limit the available power that can flow through the Zener by strategically selecting a properly sized resistor.