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What is a Voltage Regulator?

Sam Sattel

eagle-academy

Regulators, Mount Up:
The Voltage Regulator, and How It Protects Your Circuit

Whether it’s your car, laptop, or smartphone, every electronic device needs some protection from fluctuating voltages. These days, with devices getting packed tighter than ever with sensitive components like microprocessors and integrated circuits (ICs), even the slightest change in voltage can wreak havoc on your carefully designed circuit. So what can a sensitive component do when it requires protection? It needs a regulator to keep voltages running stable and smooth from input to output.

Voltage Regulators at a Glance

In the world of electronic components, the voltage regulator is one of the most widely used, but what does this IC do? It provides a circuit with a predictable and fixed output voltage at all times, regardless of the input voltage.

lm7805-linear-regulator

The LM7805 is one of the most popular linear voltage regulators around. (Image source)

How a voltage regulator achieves this task is ultimately up to the designer. Some voltage can be controlled by a simpler Zener diode, while other applications require an advanced topology of linear or switching regulators. At the end of the day though, every voltage regulator has a primary and secondary goal:

Primary: To generate a steady output voltage of a circuit in response to variations in an input voltage conditions. You might have 9V in, but if you only want 5V out, then you’ll need to step it down (Buck) with a voltage regulator.

Secondary: Voltage regulators also work to shield and protect your electronic circuitry from any potential damage. The last thing you want is to fry your microcontroller because it couldn’t handle a spike in voltage.

When it comes to adding a voltage regulator to your circuit, you’ll typically work with one of two types – Linear Voltage Regulators or Switching Voltage Regulators. Let’s see how both of these work.

Linear Voltage Regulators

This type of regulator acts as a voltage divider on your circuit and is the kind of regulator commonly used when you’re designing low power and low-cost applications. With the linear regulator, you’ll be taking advantage of a power transistor (BJT or MOSFET) that plays the role of a variable resistor, raising and lowering the output voltage of your circuit as your input supply changes.

Regardless of what kind of load is placed on your circuit, a linear voltage regulator will always keep pace to provide you with a constant, steady output voltage. For example, a 3-pin linear voltage regulator like the LM7805 provides a consistent, 5 volt 1 amp output so long as the input voltage doesn’t exceed 36 volts.

lm705-linear-regulator

The LM705 wired in series to provide a stable output voltage. (Image source)

The downside to this type of regulator ultimately comes down to how it functions. Because it behaves like a resistor to stabilize voltage, it ends up wasting a ton of energy as it converts resisted current into heat. This is why linear voltage regulators are ideally suited for applications where power requirements are low, and the difference between input and output voltages is minimal. Let’s compare two different voltage regulation situations to see how a linear regulator stacks up:

With a 10 volt input source that gets stepped down to 5 volts with an LM7805, you’ll end up wasting 5 watts and only getting 50% efficiency from your efforts.

Take the same LM7805 regulator and give it a 7 volt input stepped down to 5 volts, and you’ll end up only wasting 2 watts and achieving 71% efficiency.

As you can see, the lower your initial input power requirements, the more efficient your linear voltage regulator can be. When working with these regulators in your own circuit, you’ll typically encounter two variations, either as a Series or a Shunt.

Series Voltage Regulator

This conventional regulator has a Zener diode controlled transistor in series with the load. Here the regulator uses as a variable element (transistor in this case), ramping resistance up and down depending on a variable input voltage to provide a steady and consistent output voltage.

simple-series-regulator

A simple series voltage regulator circuit providing a regulated DC output. (Image source)

Shunt Voltage Regulator

This application works similar to a series voltage regulator but isn’t wired in series. All excess voltage is still sent to ground through the same process of variable resistance, which again wastes energy. You’ll most commonly see shunt regulators being used in:

  • Precision current limiters
  • Voltage monitoring
  • Adjustable voltage power supplies
  • Error amplifiers
  • Current source and sink circuits
  • Low output voltage switching power supplies
transistor-shunt-regulator

The Shunt voltage regulator isn’t wired in series but still sends excess current to ground. (Image source)

Overall, if you find yourself working with a low power and low-cost application where power conversion efficiency is not a primary focus, then a linear voltage regulator will be your choice. Here are some final advantages and disadvantages to keep in mind before choosing the linear regulator for your next project:

 

Advantages Disadvantages
  • Has lower electromagnetic interference and noise than switching regulators
  • Very energy inefficient option if the difference between your input and output voltage is high
  • Has a quick response time to changes in load or line voltages
  • Will often require the addition of a heatsink to dissipate all of the wasted energy
  • Provides a steady and consistent low output voltage, ideal for low power applications
  • You don’t have the option to get an output voltage higher than your input

Switching Voltage Regulators

Switching regulators are perfect when you have a large difference between your input and output voltages. When compared to linear voltage regulators, switching wins hands down in power conversion efficiency. However, all of this added efficiency also invites greater complexity into your circuit.

You’ll find that switching regulators have an entirely different internal circuitry, using a controlled switch to regulate the voltage.  This is why it is called a switching regulator.

How does a switching regulator work? Instead of constantly resisting an input voltage and sending it to ground as a sink, switching regulators instead stores and then delivers the charge in smaller pieces to the output voltage based on the feedback. By feeding an output voltage back into the switch, the regulator gets a constant check-in on whether it needs to increase or decrease the timing of the voltage chunks to output.

Switching-Regulator-Circuit

Switching regulators get a bit more complex. (Image source)

A switching regulator maintains its charge level through the help of a transistor which turns on when its storage requires more energy, and off when it’s at the desired output voltage. This helps to provide a much more energy efficient method for managing output voltage levels with a kind of dam-like system that isn’t just resisting the flow of an input voltage, but instead is reacting to changes in voltage and switching on/off as needed.

There are some downsides to this on/off switching process though. The faster that your switching regulator switches, the more time it will spend moving from a conductive to a nonconductive state, which leads to an overall reduction in conversion efficiency. You’ll also get a lot more noise in your circuit with a switching regulator than you would with a linear voltage regulator.

However, unlike linear voltage regulators, switching regulators are a lot more diverse in their available applications. These regulators don’t just step down or boost your voltage, but it can also invert it. Here are the three techniques that switching voltage regulators are known for:

Boosting (Step-Up)

This method produces a higher regulated output voltage by boosting the input voltage.

lm2577-switching-regulator-schematic

This circuit is boosting up a 5V input to 12V at its output. (Image source)

Bucking (Step-Down)

This technique produces a lower regulated output voltage based on a variable input voltage, similar to how a linear regulator works.

buck-switching-regulator

This circuit is bucking down an 8-40V input to 5V at its output. (Image source)

Boosting/Bucking (Inverter)

This technique is a kind of hybrid, providing the designer with the ability to step up, step down, or invert an output voltage as needed.

Overall, if you’re working with a sophisticated design where power conversion efficiency is a concern and the differences between input and output voltages are high, then switching regulators are the way to go. Here are some final advantages and disadvantages to keep in mind before choosing this regulator for your next project:

Advantages Disadvantages
  • Achieves a much higher power conversion efficiency than linear regulators, 85%+
  • Produces more electromagnetic interference and noise than linear regulators
  • Does not require the addition of a heatsink on your board, saving space
  • Requires more complexity and additional components on your layout
  • Can easily handle power applications where there’s a wide range between input and output voltages
  • Additional components add to overall project costs, not ideal for low cost or budget projects.

Staying Simple – Zener Diode

Many designers might not need to deal with the complexity of linear or switching voltage regulators. In these situations, we can rely on an even simpler solution for regulating voltage with a Zener diode. This one component alone can in some cases provide all the voltage regulation you need, without requiring any special parts.

The Zener diode gets the job done by shunting all excess voltage above its threshold to ground. However, all of this simplicity does come with limited abilities, and you’ll typically only use Zener diodes as voltage regulators for very low power applications.

Which Regulator Do You Need?

All designs are unique, and there’s not one universal regulator that will meet the needs of every engineer. Rather, you’ll want to evaluate each new project on a case-by-case basis and ask yourself the following questions:

  • Does your design requirement call for low output noise and low electromagnetic interference? If so then linear regulators are the way to go.
  • Does your design require the fastest response to input and output disturbances? Linear regulators win again.
  • Does your design have strict cost constraints and you need to account for every dollar? Linear regulators are the economical choice.
  • Does your design operate at a power level above a few watts? In this situation switching regulators are cheaper since they don’t require a heatsink.
  • Does your design require a high power conversion efficiency? Switching regulators are the way to go and offer efficiencies at 85%+ for step-up and step-down applications.
  • Does your device operate solely off of a DC power supply and you need to step up the output voltage? Switching regulators will handle this.

Still not sure which realtor to choose? Here are some other details to consider in How do I pick the best voltage regulator for my circuit? from Power Electronics.

Regulators, Mount Up

Whichever device you’re designing, it’s going to need some serious protection from fluctuating voltages. Voltage regulators are the perfect tool for the task, capable of providing a steady output voltage to ensure your circuit works as intended. Which voltage regulator you need ultimately comes down to the requirements of your design. Working with a low power and low-cost application where power efficiency conversion isn’t a concern? Linear regulators might be the way to go. Or maybe you’re working on a design that’s more complex, requiring voltages that can be stepped up and down as needed. Consider switching regulators if that’s the case. Whichever regulator you choose, you’ll be protecting your circuit from the dangers of those voltages out in the wild.

Did you know that Autodesk EAGLE includes a ton of free voltage regulator libraries ready for you to use in your next project? Try Autodesk EAGLE for free today!

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