An Introduction to Voltage Regulators

Voltage Regulators

Voltage Regulators

A voltage regulator is found in electronic devices, and it is used to maintain the voltage of the power source so that it stays within acceptable limits. Voltage regulators are designed several different ways – it could be a simple “feed-forward” design, it may include negative feedback control loops, or it could use an electromechanical mechanism, or electronic components. Also, voltage regulators may be used to regulate one or more AC or DC voltages, depending on the design.

The voltage regulator is a very crucial and critical part of a power source. Without proper voltage regulators, most electronic devices or projects would not be able to operate accurately. Voltages must be kept within the approved range by the electrical equipment, or else it may burn out and stop working. This is the voltage regulators main duty. This device is very often “used in motor vehicles of all types to match the output voltage of the generator to the electrical load and to the charging requirements of the battery.”*

According to www.britannica.com:

                In motor vehicles, voltage regulators rapidly switch from one to another of three circuit states by means of a spring-loaded, double-pole switch. At low speeds, some current from the generator is used to boost the generator’s magnetic field, thereby increasing voltage output. At higher speeds, resistance is inserted into the generator-field circuit so that its voltage and current are moderated. At still higher speeds, the circuit is switched off, lowering the magnetic field. The regulator switching rate is usually 50 to 200 times per second.

Voltage regulators are not only used in motor vehicles, they are used in a wide range of devices, including computer power supplies, auto alternators, central power station generator plants, and countless others. They may also be installed at a substation, or possibly along distribution lines in an electric power distribution system. This is so all customers can receive steady voltage, no matter how much power is drawn from the line.

Just as they do in motor vehicles, voltage regulators perform the same job in large-scale power-distribution systems as well – which is minimizing variations in voltage so that it can protect the equipment that is using the electricity. The regulators are in the substations or on the feeder lines. There are two types of regulators that are used – step regulators and induction regulators.

  • Step regulators – switches regulate the current supply
  • Induction regulators – supplies a secondary, continually adjusted voltage to even out current variations in the feeder line

The output voltage can only be held “roughly” constant. The regulation is specified by two measurements:

  • Load regulation: the change in output voltage for a given change in load current
  • Line regulation, or input regulation:  the degree to which output voltage changes with input (supply) voltage changes – as a ratio of output to input change or the output voltage change over the entire specified input voltage range

Some other important parameters are:

  • Temperature coefficient of the output voltage is the change with temperature
  • Initial accuracy of a voltage regulator reflects the error in output voltage for a fixed regulator without taking into account temperature or aging effects on output accuracy
  • Dropout voltage is the minimum difference between input voltage and output voltage for which the regulator can still supply the specified current. A low drop-out regulator is made to work well even with an input supply only a volt or so above the output voltage.
  • Absolute maximum ratings are defined for regulator components, specifying the continuous and peak output currents that may be used, the maximum input voltage, maximum power dissipation at a given temperature, etc.
  • Output noise and output dynamic impedance may be specified as graphs versus frequency, while output ripple noise may be given as peak-to-peak or RMS voltages, or in terms of their spectra
  • Quiescent current in a regulator circuit is the current drawn internally, not available to the load, normally measured as the input current while no load is connected

One type of voltage regulator, known as a linear regulator, is based on devices that operate in their linear region. More current designs use one or more transistors, sometimes within an Integrated Circuit. Linear Designs have a very “clean” output with little noise into their DC output. All linear regulators require a higher input than the output. If the input voltage reaches the preferred output voltage, the regulator will “drop out”.

Another kind of regulator, called switching regulators, quickly switch a series device on and off.  The switches’ duty cycle sets how much charge is transferred to the load. A linear regulator has a similar mechanism that controls this.  Also, like linear regulators, nearly-complete switching regulators are available as integrated circuits.

Linear and switching regulators each have their advantages and disadvantages. For instance, linear regulators are best when both a low output noise is required, as well as when a fast response to input and output disturbances is required.  

*Additional quotations and information courtesy of www.britannica.com, as well as www.wikipedia.org.

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