A shunt regulator, sometimes known as a shunt voltage regulator, is a kind of voltage regulator in which the regulating element shunts current to ground. The shunt regulator works by keeping a constant voltage across its terminals and absorbing extra current to keep the voltage across the load constant.
In general, voltage regulators can be divided into two main categories: active and passive. Active regulators require an external power source and some sort of energy storage device such as a battery or capacitor. They generate their own output voltage based on the input voltage and how much energy is stored in the battery. Active regulators are used when maximum efficiency is required at all times because they provide continuous regulation of voltage and power to loads. Active regulators include DC-to-DC converters, linear regulators, and switch-mode regulators.
Passive regulators do not require an external power source and instead use one circuit component to produce a constant output voltage. Passive regulators include resistors, thermistors, and diodes. A disadvantage of using passive components for voltage regulation is that they tend to be large compared to active elements like transistors.
Shunt regulators are a type of passive voltage regulator that use a resistor to absorb excess current from an electrical circuit to prevent overloading or destroying other components in the circuit. A shunt regulator does not need to be switched on and off like an active regulator, so they are usually more efficient than active regulators of equal capacity.
The basic Zener diode circuit, in which the Zener diode operates as the shunt element, is one of the most popular examples of a shunt regulator. It can be used to provide a stable voltage source for other circuits on the same IC or on different ICs. For example, an LED driver might use several of these regulators to control the output voltage from 5V to 15V. The energy from the battery is sent to each regulator in turn; when there is not enough power left to run all the regulators, then only the highest-voltage unit will remain activated.
Zeners are semiconductor diodes that have their resistance increase dramatically if their voltage exceeds a certain value (typically around 14V). This means they can be used as voltage sources instead of resistors, providing that the higher voltage does not appear across any other component. For example, if you wanted to create a 3VDC supply from a single 9V battery, you could do this with two Zeners in series, giving you approximately 14V across both devices. However, because these diodes leak current even when exposed to air, they need to be used in parallel with another device that provides some form of isolation.
A shunt is an electrical device that creates a low-resistance channel for a current. This allows the current to flow to a different location in the circuit. Shunts are sometimes known as ammeter shunts or current shunt resistors. The word "shunt" comes from the word "shunter", which means "someone who cuts wires". A shunt is used when there is not enough room to fit an entire resistor in the circuit. For example, if the circuit requires a 1K resistor but only has access to 500-ohm shuns, then those shuns have to be connected in parallel to get the required resistance.
There are three main uses for shunt circuits: measurement, protection and control. In measurement applications, such as power meters and voltage regulators, a shunt monitors the current flowing through a component such as a transformer or power supply. The information from the shunt can then be used by the meter or controller to adjust the operation of the device being measured.
In protection applications, such as circuit breakers and contactors, a shunt prevents current from flowing through a section of the circuit if something goes wrong with another part of the circuit. For example, if there is a short circuit on one side of a diode, the current will flow through it until it fails. When this happens, the protector senses the loss of current and acts accordingly.