Types of Voltage Regulators

An Explanation of Three Different Types of Voltage Regulators

An assortment of 78xx series ICs
BotMultichill/Wikimedia Commons/CC BY-SA 3.0

When a steady, reliable voltage is needed, voltage regulators are the go-to component. They take an input voltage and create a regulated output voltage regardless of the input voltage at either a fixed voltage level or adjustable voltage level (by selecting the right external components).

This automatic regulation of the output voltage level is handled by various feedback techniques, some as simple as a Zener diode while others include complex feedback topologies that can improve performance, reliability, efficiency, and add other features like boosting output voltage above the input voltage to the voltage regulator.

Types of Voltage Regulators

There are a number of types of voltage regulators that range from very affordable to very efficient. The most affordable and often the easiest type of voltage regulator to use are linear voltage regulators.

Linear regulators come in a couple of types, are very compact, and used often in low voltage, low power systems.

Switching regulators are much more efficient than linear voltage regulators, but they are harder to work with and more expensive.

Linear Regulators

One of the most basic ways to regulate voltage and 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 effective series resistance of the regulator based on a feedback voltage, essentially becoming a voltage divider circuit.

This lets the regulator output an effective constant voltage regardless of what current load is placed on it, up to its current capacity.

One of the big downsides to linear voltage regulators is the large minimum voltage drop across the voltage regulator, 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 would have to dissipate at least 2 watts if it was delivering a 1 amp load (2 volt voltage drop times 1 amp).

The power dissipation gets worse the larger the difference between the input and output voltage. So, for example, while a 7 volt source regulated to 5 volts delivering 1 amp would dissipate 2 watts through the linear regulator, a 10 volt source regulated to 5 volts delivering the same current would dissipate 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 down side to linear regulators is that they are very inefficient, which is where switching regulators come into play.

When high efficiency is needed or a wide range of input voltage is expected, including inputs voltages below the desired output voltage, 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, and the values of the components have much more of an impact on the overall performance of switching regulators than linear regulators.

There are also more design challenges in using switching regulators effectively without compromising the performance or behavior of the rest of the circuit due to the electronic noise that the regulator can generate.

Zener Diodes

One of the simplest ways to regulate voltage is with a Zener diode. While a linear regulator is a pretty basic component with few extra components required to work and very little design complexity, a Zener diode can provide adequate voltage regulation in some cases with just a single component.

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

Unfortunately, Zeners are often very limited in their ability to handle power which limits where they can be used as voltage regulators to very 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.