How to Use DC Regulators/Converters

Updated 15 February 2017

So, you might have the best project in the world, an amazing idea and design, but no matter how clever your circuitry or how advanced your prototype is, unless you can power your project correctly, it all counts for nothing. Often you will need different voltage levels for different parts of your circuit; 12V for a motor, 5V and 3.3V for your microcontrollers, and perhaps 9V for a relay. Now it wouldn’t make sense to use individual power supplies for each requirement. You want to simply connect a USB cable, power pack, or battery up and have that power your entire circuit. That’s all well and good, but you’ll need a way to convert one voltage to another, and control how much current your circuit can draw in case something goes wrong.

Today we’re going to look at different types of voltage regulators and converters, how to use off-the-shelf modules, how to make your own, and how they work. Before we get started, we’ll be dealing with different electrical concepts and electronic components so we recommend taking a look at our Analogue Electronics Crash Course first. Now let’s dig in!

Useful Terms

Pololu step-up regulatorBefore we dive into the hardware, let’s take a moment to discuss a couple of common terms used for voltage regulation and conversion.

  • Load Regulation: This defines how much the output voltage changes in relation to the output current being drawn. In an ideal world, you could draw as much current as you want and the output voltage wouldn’t change, but Ohms law makes that impossible.
  • Line Regulation: This is how much a change in the input voltage affects the output voltage. Devices with high standards of line regulation will give a rock solid output voltage regardless of noise, or changes to the input voltage (within the standard operating range).
  • Drop Out Voltage: This value (given in datasheets) specifies how low the input voltage can be above the desired output voltage on a step-down regulator before the output voltage becomes unreliable. On standard regulators, it’s a couple of volts, however, special Low-Dropout regulators (LDO) can have a dropout voltage as little as 1V.

So anyway, enough talk of terms and clarification, let’s get to the hardware.

Zener diodeZener Diodes

A Zener diode is an interesting variation of a standard diode. Whilst it possesses the valve-like functionality of a regular diode, when it is reverse-biased at a certain voltage, it will conduct the opposite way. Simply put this means that if you apply a voltage equal to or greater than it’s ‘Zener voltage’, it will conduct in the opposite direction to a normal diode. This is incredibly useful as it allows as to use these Zener diodes to create simple voltage regulators.

Switching vs. Linear Regulators

Zener diodes are all well and good, but if you want a regulator that’s a bit more robust, then you’ll want a solution in the form of an IC (Integrated Circuit). There are two main types of regulators; switching and linear regulators. They operate slightly different from device to device however both types of regulators work in a different way.

A switching regulator operates by rapidly switching the supply voltage and storing energy in an inductor which allows it to convert an input voltage into a higher or lower voltage. Because the switch is operating as either fully on or fully off, there is little energy wasted and makes switching regulators highly efficient, although the switching creates some noise in the output voltage and because of that, switching regulators aren’t recommended for audio use where that switching may become audible.

A linear regulator, however, operates by using a shunt or feedback loop with a transistor to generate the required voltage. Linear regulators are much simpler and cheaper devices, however, because of their operation, they waste a lot of energy which is converted into heat. Linear regulators can only operate as ‘Buck’ type converters which mean they can only reduce a voltage, not increase it (boost).

Both types of regulators are available as either fixed or variable. There are different methods for each, however, this makes them far more versatile as it allows a range of output voltages to be achieved from a single input voltage usually via a mechanical control, or fancier regulators may provide a digital interface for a microcontroller to adjust the output voltage.

We can categorise both types of regulators with the following general characteristics:

Linear Regulators:

  • Simpler
  • Less efficient (consume more power and hence generate more heat than switching regulators)
  • Cheaper
  • The power dissipation of a linear regulator is given as P = (Vin – Vout) x load current. This shows us that the closer the output voltage is to the input voltage (with the dropout voltage taken into consideration), the more efficient a linear regulator is
  • Only capable of ‘Buck’ type conversion (step down regulation)
  • Low noise

Switching Regulators:

  • More complex.
  • More efficient with a wide range of input voltages (often used after a rectifier for regulating mains power)
  • Higher noise due to the high-frequency switching
  • Capable of Buck and Boost conversion (step-down/step-up)

Linear Regulators

For many projects, a simple linear regulator will do the trick. Take, for example, the venerable L7805 which is a 3-pin linear, step-down regulator which outputs 5V. It’s been used in millions of designs and products across the globe and is a good choice if you want a solid 5V supply for digital systems at a low cost. Shown below is a sample setup for an L7805 including smoothing capacitors.

L7805 sample circuit

Switching Regulators

So which one should you use, a Buck converter, a Boost converter, or a Buck-Boost converter? Well, it depends, remember that Buck = step-down, Boost = step-up, and Buck-Boost = step-up/step-down. Bear in mind that the terms 'buck' and 'boost' only refer to switching regulators, not linear ones. 

Linear regulators are nice and simple, however, many projects require a high efficiency that only switching regulators can provide. For most applications, people tend to gravitate automatically towards Pololu regulators for their low-cost/high-performance design, and a wide range of voltages and models which make them ideal for all kinds of applications.

Calculating Efficiency

One thing to keep in mind is that Power is a function of Voltage x Current (P=VI). Voltage regulators/converters are able to handle a certain amount of power. So if you have an input voltage of 5V that you’re stepping up to 10V, if your power supply can handle 500mA of current, then according to P=VI, you’ll only have 250mA available on the output. THEORETICALLY. That is before you take into account the conversion losses. When considering a voltage regulator for your application, you should always take a look at the datasheet which will provide efficiency graphs which compare different input/output voltages and the current draw. Take a look at the graph below:

 Voltage regulator efficiency graph

As you can see, the closer the input voltage is to the output voltage, the higher the efficiency (lower power wastage) especially as you draw more and more current. For this reason, it’s important to carefully plan how you will use voltage regulators in your project. If you’re powering everything from a 12V LiPo and you use a 5V regulator for something, don’t then regulate that 5V back up to 9V for something else. That’s two conversions that occur and accrue power loss. Tap directly onto the 12V output, and it you are using a variable power supply, such as a LiPo battery which has a higher voltage when fully charged, than when depleted, ensure that the lowest voltage will still work with your regulators.

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