What Is a Voltage Regulator and What Does It Do?

A voltage regulator is a component that gives you a stable output voltage, no matter if the input voltage changes. It’s an integrated circuit (IC), usually with three or more pins.

A typical example of when you need a voltage regulator is if all you have is a 9V battery, but your device needs 5V. A voltage regulator can take those 9V as input and create a nice and stable 5V output that you can use to power your device.

Or if you need different voltage levels for a circuit you’re building. Let’s say you have a circuit with a microcontroller that needs 5V and a motor that needs 12V. Instead of using two power supplies, you can use just one 12V supply and add a voltage regulator to provide 5V for the microcontroller.

How To Connect a Voltage Regulator

Usually, you need a few extra components connected to your voltage regulator to make the output a bit more stable. At least a capacitor or two. But it depends on the voltage regulator you have.

You’ll find info about how to connect a specific voltage regulator in its datasheet.

For example, the voltage regulator 7805 is a common one. It gives you 5V out. From the 7805 datasheet, you can find this example circuit that shows that you need two capacitors:

Types Of Voltage Regulators

There are two main types of voltage regulators that are worth knowing about:

• Linear Voltage Regulators
• DC-DC Switching Regulators

The linear voltage regulator is the simplest one that only requires a couple of capacitors and maybe a resistor or two to work. But it can only create an output voltage that is lower than the input.

Examples of linear regulators are the 7805 and the LM317 with an adjustable output voltage.

The DC-DC switching regulator is a bit more complex and also needs an inductor and a diode to work. One example is the LM2596. But often you can find these as small modules (look for DC-DC converters) that have everything you need on the board.

Some DC-DC converters can give you a higher output voltage than what you put in.

Linear vs Switching Regulators

The main difference between the two regulator types is that a linear regulator wastes much more power than a switching regulator. So the linear regulator can easily get really warm if you don’t provide good cooling. And if it gets too warm, it shuts down.

Also, the switching regulator is the only one that can give you a higher output voltage than the one you put in. A linear regulator will always give you a lower output voltage.

How Linear Voltage Regulators Work

There are many ways to design a linear voltage regulator. Here’s maybe one of the simplest:

The output will always be the Zener voltage of the Zener diode minus the V_BE voltage of the transistor. V_BE is usually around 0.6V to 0.7V. So with a 5.6V Zener diode, you’ll get around 5V on the output.

If the output voltage goes up beyond 5V, that means V_BE becomes lower. That would make the transistor reduce the current so that the voltage goes down again. If the output goes lower than 5V, the opposite would happen.

Low-Dropout (LDO) Regulators

With linear voltage regulators, you often need to provide an input voltage that is at least 2V higher than the output you want. But a low-dropout, or LDO regulator, is a linear regulator where you can get away with an input voltage that is much closer to the output voltage you want.

How Switching Regulators Work

The other main type is the switching regulator. This is a voltage regulator that is switching the input voltage on and off and uses some smart circuit tricks with an inductor to convert the voltage in a much more power-efficient way.

There are 3 main types:

• Buck (or step-down) converter – Can convert to a lower voltage
• Boost (or step-up) converter – Can convert to a higher voltage
• Buck-boost converter – Can convert both to a lower and a higher voltage

Here’s the basic concept of a buck converter:

To really understand how this works, you need to understand how the inductor works.

When the switch is pushed, current flows into the inductor, capacitor, and load from the battery. Both the inductor and the capacitor gets charged. When the switch is released, the stored energy in the inductor and capacitor provides the current for the load.

In real life, the switch is replaced by a transistor. And there is a sensing mechanism that checks the output voltage and turns the transistor on and off faster (to get more voltage) or slower (to get less voltage).

How to Choose a Voltage Regulator

Choosing a voltage regulator is pretty easy. Here are a few example cases:

• Is your input voltage just a few volts higher than your desired output voltage? Then you can use any voltage regulator.
• Is your input voltage just a few volts higher than your desired output voltage, but you need a lot of current? Then the best choice is a Buck converter since a linear regulator would get very hot.
• Is your input voltage much higher than the output voltage you need (ex 24V input and 5V output)? Then you most likely need a Buck converter.
• Do you need the output voltage from the regulator to be higher than the input? Then you need a Boost or a Buck-Boost converter.
• Is your input voltage unstable and can be both higher and lower than the output voltage you want? Then you need a buck-boost converter.

Questions?

Let me know what questions you have about the voltage regulator in the comment section below. I’ll do my best to answer them and update the article accordingly!

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