Encyclopedia of Electrical Engineering
Encyclopedia of Electrical Engineering

Voltage Regulation

What is the purpose of voltage regulator?

Voltage regulator used to keep the voltage in a circuit relatively close to a desired value. A voltage regulator is designed to automatically regulate voltage level. It basically steps down the input voltage to the desired level and keeps that in that same level during the supply. This makes sure that even when a load is applied the voltage doesn't drop.
To help us anticipate the expected response of a supply, a defining quantity called voltage regulation (abbreviated VR; often called load regulation on specification sheets) was established. The basic equation is the following:
$$\bbox[5px,border:1px solid red] {\color{blue}{V_R = {{V_{NL} - V_{FL}} \over V_{FL}} \times 100\%}}$$Eq.(1)
The examples to follow demonstrate that the smaller the voltage or load regulation of a supply, the less will the terminal voltage change with increasing levels of current demand. For the supply above with a no-load voltage of 20.1 V and a full-load voltage of 18.2 V, at 275.2 mA the voltage regulation is $$\begin{array} {rcl} V_R &=& {{V_{NL} - V_{FL}} \over V_{FL}} \times 100\%\\ &=& {20.1 V - 18.2 V\over 18.2 V} \times 100\%\\ & =&10.44\% \end{array}$$ which is quite high, revealing that we have a very sensitive supply. Most modern commercial supplies have regulation factors less than 1%, with 0.01% being very typical.
Voltage regulators are one of the most common electronic components, since a power supply frequently produces raw current that would otherwise damage one of the components in the circuit. Voltage regulators have a variety of specific functions, depending on their particular application.

Passive Voltage Regulation

A passive voltage regulator may be used if the power supply consistently produces a voltage greater than what the circuit require. This type of voltage regulator essentially consists of a resistor reduces the incoming voltage to the desired output level and dumps the excess energy as heat. A heat sink is require to dissipate this unneeded heat.

Active Voltage Regulation

Circuits that require the voltage to increase will require an active voltage regulator. Such voltage regulators typically use negative feedback loop to control the voltage. This means that a voltage outside the desired range causes the voltage regulator to bring the voltage back to its specified range.

Transformer Mains Regulators

The transformer on a mains line has multiple taps that control the circuit voltage. When the output voltage of the mains regulator drops below a minimum value, the regulator connects to a tap with a higher voltage. Similarly, when the output voltage rises above a maximum value, the regulator connects to a tap with a lower voltage.

AC Voltage Stabilization

AC voltage stabilization refers to the regulation of relatively minor fluctuations in AC voltage. These voltage regulators are routinely used in a home to keep the voltage within the range needed by household appliances.

DC Voltage Stabilization

DC voltage stabilizers control the voltage in a circuit that uses a battery. They use a shunting device such an avalanche breakdown diode, voltage regulator tube or zener diode to conduct only at a specified voltage. The shunt will carry as much current as needed to output this voltage. In order for a DC voltage stabilizer to operate safely, the current from the power supply may not exceed the maximum safe voltage limit of the shunting device. This is typically accomplished by including a series resistor in the circuit.