An Overview of Voltage Regulators

Voltage regulators are used as a part of modern-day electrical circuitry. The purpose of a voltage regulator within a circuit generally is to keep a constant output voltage that is different from the input voltage given to the voltage regulator. In some cases, voltage regulators may also be made to keep voltage throughput constant when the input voltage is variable, but the device being powered requires a constant voltage instead.

Voltage regulators are an important part of the safe and continued function of a circuit or device. Excessive voltage can be damaging to a device’s internal circuitry, and can fry sensitive components like motherboards and microcontrollers, in devices that have such components inside them. For that reason, almost every advanced device on the market today will use some form of voltage regulation inside it.

Industry and Academics

To address this demand, a large market of voltage regulator manufacturers has popped up. There are companies that specialize only in the making and manufacturing of voltage regulators, which are then installed in the circuits of other devices manufactured by other companies. There are also engineering firms that specialize in making voltage regulators that are increasingly efficient and compact; as devices get smaller, the space that can be allocated within the device for controlling input voltage gets correspondingly constricted. Over time, this has put demand on voltage regulator companies to reduce the size of their voltage regulation products, while keeping constant or even improving the devices’ performance.

Besides the industrial aspects of voltage regulator development, the study of voltage regulation is also a part of current academics. Typically, academics working on this are in engineering schools and chemistry departments, as opposed to physics departments. The prevailing view today is that the remaining advances in voltage regulation will be made by improved construction (engineering) and use of novel materials (chemistry) that step up the performance of current regulator designs. Physicists studying electromagnetism have largely moved on from investigations in this area, believing that their field’s ability to advance voltage regulators has been tapped out, at least for now. Absent paradigm-shifting advances in physics, it is unlikely voltage regulation and modulation will again become a topic of study for many physicists working at the professional level.

Automation and Digitization

Today, commercial voltage regulators are both automated and digitized; that is, those using them can set them to output a particular voltage, usually by means of a keypad or dial built onto the regulator. These regulators are most often used by hobbyists working on electrical projects, electricians, engineers, and students working in the realms of electricity and magnetism.

On the other hand, many voltage regulators in consumer electronics are neither automated nor in any way digital. They use mechanical means to hold voltage constant for the device. And since the devices generally do not need much fluctuation in the voltage supplied to them, there is no need for user input to determine what voltage will be supplied.

Adjustable Voltage Regulators

Adjustable regulators are, as their name suggests, adjustable. This means that the output voltage can be moved up and down as needed. In some devices, the adjustment is done by the user, who is responsible for deciding on his or her own what voltage is appropriate for the situation. The output voltage might vary based on the power needs of the device, or based on the voltage that is supplied to the device from the power source.

For instance, a device might be used with one power source that does not supply enough voltage to warrant voltage modulation, and as long as that power source is in use, the voltage regulator does not need to be engaged. However, when such a device his hooked up to a powerful supply of electricity, the voltage regulator would need to be engaged to prevent excessive voltage from frying or doing damage to the internal components of the device.

A good example of such devices that require user -controlled voltage regulators is a hair dryer. Often times, hairdryers are equipped with voltage regulating knobs for when they are used in countries outside the one where they were manufactured. In those cases, the user will have to turn the regulator to the proper setting, or risk damaging his or her device. This is because the voltage supplied from the power grid is not the same in every country. Power conversion—also known as voltage regulation—is needed to make a device like a hair dryer work outside its native power zone.

The LM317 Voltage Regulator

The LM317 is kind of voltage regulator that was developed in 1970 by two employees of National Semiconductor, Robert Dobkin and Robert Widlar. The LM317 can output anywhere from 1.25 volts to 37 volts, and it allows the user or product designer to adjust the output voltage dynamically, without any requirement that the output voltage be set for the long term.

The flexibility and power of the LM317 have ensured that it remains a popular voltage regulator to this day. Additionally, forty some years after its original version, the LM317 has become quite inexpensive to manufacture and purchase, which makes it popular both among amateurs working with electronics, and professionals designing products for consumer and industrial markets. LM317s are available for purchase from most electronic equipment stores, and from some non-specialized stores as well, like Home Depot and Lowes Home Improvement. This makes the LM317 one of the most widely distributed standalone voltage regulators of all.

The LM317’s popularity owes partly to the fame of one of its inventors, Robert Widlar. As a young man, Widlar established himself as an expert in the fields of semiconductors, computer chips, and—more generally—the electrical modulation techniques that are essential to semiconductors and microchip technology. In his mid-30s, Widlar retired unexpectedly from the tech field and moved to Mexico. Several years later, he unretired and returned to California to work at National Semiconductor. It was while at National Semiconductor that he collaborated with Dobkin to invent the LM317. Not long after that, Widlar once again retired to Mexico, and while living there, died prematurely and unexpectedly at the age of 53. His death and iconoclastic life helped enshrine his inventions in the annals of computer and engineering history, and gave the LM317 a great deal of publicity within those fields.

LM317 Specifications

Every voltage converter comes with a list of specifications that describe how much voltage it can accept, how much it can output, what temperatures it operates at, and how many amperes it can output and accept.

The LM317 is able to output voltages between 1.25 volts and 37 volts. The difference in the voltage accepted and the voltage output can be anywhere between three and 40 volts. The LM317 operates most efficiently when the air around it is at temperatures between zero degrees Celsius and one hundred twenty five degrees Celsius. Additionally, its output must fall beneath 1.5 amperes and its minimum input current is at least 10 milli-Amps. Outside these parameters, the operation of the LM317 suffers. When the input values are sufficiently out of these ranges, then the device can degrade, break down, or fail to regulate voltage entirely, which may cause damage to the device the LM317 is intended to protect.

Linear Regulators

Linear regulators are the most common type of regulator on the market, and they are the most inexpensive and easiest type of regulator to produce for a customer.

Linear regulators are distinguished by their ability to produce a constant output current, without any deviations, increases, or decreases. To achieve this, linear voltage converters pass the power through a transistor, which steps down the supply voltage to the correct levels. Usually, this dissipation occurs as a result of power being dissipated into waste heat. The amount of power wasted as heat can be increased or decreased with a switch or digital meter, or in some cases, it is fixed and cannot be changed.

One challenge of linear converters is keeping them cool. Because they dissipate heat into the environment, the voltage regulators themselves tend to assume most of the heat, and consequently warm to levels that can degrade their materials, or compromise their performance. This is one of the chief reasons that linear converters will have a “maximum step down” indicated on their electrical component datasheets. When the converters are asked to step down a greater amount of voltage than this for long periods of time, they tend to become overheated. In a theoretical construct, the maximum step down voltage is calculated in part based on how much heat the voltage regulator can absorb before it overheats. More practically, the heat absorption number is also dependent on other factors, such as how hot the ambient environment is, and the conductive properties of the other materials attached to the voltage regulator.

Linear converters are the most simple converters in common use, and also relatively inefficient. Devices that demand greater power efficiency, or which cannot deal with the absorption of much waste heat, will instead use switching-current voltage regulators, or switching-current power supplies.

Voltage Regulator Terminology

Now that you understand some of the basic aspects of voltage regulators, have a look at some of their more technical points. Here follows a listing of some key characteristics of voltage converters, with a brief explanation of each and an overview of its significance.

Maximum Output Current

In electromagnetics, current and voltage are closely related. Voltage is measured in volts, of course, and current is measured in amps. A voltage current will output a certain voltage, but it will also have a maximum current that it can output. That current is denoted on the voltage regulator’s datasheet as “maximum output current.”

Output Voltage

This is the central characteristic of any voltage converter. Output voltage, measured in volts, is the voltage that the regulator allows to pass across the circuit. The output voltage will differ from the supply voltage by a set range of values, and it will always be less than the supply voltage, though not necessarily by a wide margin. Many voltage converters are now capable of outputting voltages just one volt beneath the supply voltage.

Mounting Type

Mounting type refers to the way in which the voltage regulator is attached to the circuit’s substrate, in classical circuitry. In more practical terms, this simply means the mechanism by which the voltage regulator is affixed to whichever section of the circuit it works on. There is a range of mounting types. Some voltage regulators are screw-mounted. Others are attached to the surface of the substrate by adhesives, magnets, or even the force of gravity. Still others are attached to a substrate that is shot through with numerous holes to allow for components to be fixed to it. When a voltage regulator is manufactured to be attached in this way, it is said to be a “through-hole voltage regulator.”


A voltage regulator is either rated to output a particular voltage, or it is capable of being calibrated to output a number of different voltages. In either case, there will be some indication of what voltage it is outputting; however, the exact voltage it does output will be slightly different from this rating. The discrepancy between the voltage it is intended to output and the voltage it actually does output is called “accuracy.”


Voltage regulators have polarity, which is how electricity is drawn across the transistors within them. One side of the regulator is positive, and the other is negative. The electricity, which is actually the flow of electrons, will flow from the negative to the positive, because electrons are repelled from negative poles and attracted to positive poles.

Minimum Input Voltage

Voltage regulators have a minimum voltage drop off of which they are capable. That is, when electricity is passed across the poles of their transistors, the voltage of the electricity has to drop by at least that amount. Adjustable regulators can decrease the voltage by more, but never any less. The minimum input voltage will be at least this number; if it were lower, voltage would drop to zero and electrical flow would cease.

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