Stabilized Power Supplies, Physics tutorial

Constant voltage power supplies:

The voltage regulator is the electrical regulator that automatically maintains the constant voltage level. The voltage regulator may be the simple design or may comprise negative feedback control loops and may be electromechanical or electronic. It may, subject to design be utilized to regulate alternating or direct current voltages.

Electronic voltage regulators are found in different devices ranging from computer power supplies where they stabilize direct current voltages used by processor and other elements, to automobile alternators and central power station generator plants where voltage regulators manage output of plant.

They are also to be found in electric power distribution systems where voltage regulators are generally installed at substations or along distribution lines so that all customers obtain steady voltage independent of how much power is drawn from line.

Real-world sources of electrical energy, like batteries, generators, or power systems, can be modeled for analysis reasons as combination of ideal voltage source and extra combinations of impedance elements.

The simple voltage regulator can be made from resistor in series with diode or tandem of diodes in series where because of logarithmic shape of diode V-I curves, voltage across diode changes only somewhat because of changes in current drawn. When precise voltage control is not significant, this design is suitable.

Feedback voltage regulators run by comparing actual output voltage to some fixed reference voltage whereas any difference is amplified and utilized to control regulation element in such a way as to decrease voltage error. This arrangement forms the negative feedback control loop. If we increase open-loop gain, it leads to the increase in regulation accuracy but decreases stability. It also results in the trade-off between stability and speed of response to changes.

If output voltage is too low that may result from input voltage reduction or load current increase, regulation element generate the higher output voltage and vice versa.

Active regulators:

The active regulator needs at least one active element like a triode valve, the transistor or an operational amplifier. Known for being extremely ineffective, shunt regulators are frequently made up of passive and simple components. They are ineffective as they shunt excess current not required by load and when more power should be supplied, more sophisticated circuits are utilized.

Active regulators are divided in classes; two most significant and universally utilized being linear series regulators and switching regulators.

Linear Regulators:

Linear regulators use devices which operate in linear region of their characteristic curve with modern designs utilizing one or more transistors or Integrated Circuit, while in switching regulator, device is forced to serve as an on/off switch.

The major benefit of linear regulators is extremely low noise introduced in their direct current output but they aren't as energy efficient as their switched counterparts. As all linear regulators need a higher input voltage than their output voltage, if input voltage approaches desired output voltage, regulator output will experience drop out and input to output voltage differential at which this takes place is called as regulator's drop-out voltage. Integration has made it possible to realize complete linear regulators as integrated circuits like 78 and 79 series; that are positive and negative voltage regulators respectively. Voltage regulator chips are either fixed or adjustable voltage regulators.

Switching Regulators:

Switching regulators as name signifies operate by rapidly switching the series active device on and off while duty cycle of switched device finds out how much electrical charge is transferred to load. This function is managed by the feedback mechanism which is like that in linear regulator and as series element is either completely conducting, or switched off, very little energy is dissipated in switching device. This result in very high efficiency related with switching regulators. In contrast with linear regulators, Switching regulators are also capable to produce output voltages that are higher than input, or output voltages of reverse polarity.

Complete integrated circuit switching regulators aren't available as power reactive elements needs in switching regulators can't be implemented on the chip, though nearly-complete switching regulators are available as integrated circuits that generally need one external component: inductor which serves as energy storage element.

The two kinds of regulators have advantages and disadvantages as given below:

Linear regulators introduce extremely little noise to the output voltage that in contrast with switching regulators that have very noisy output that generate lot of radio frequency interference if extra circuitry is not utilized to suppress output noise. Linear regulators are thus better when low output noise; mainly low radio frequency interference is needed

Linear regulators have quicker response to input and output variations of voltage and load respectively. Switching regulators on other hand are much slower and suffer more slow tracking of reference voltage and as such are less suitable for applications where fast response to input and output disturbances is required.

In low power applications, Liner regulators are more cost-effective; they cost less and need less space as complete and comprehensive designs can be implemented on the chip.

Switching regulators are superior to linear regulators where power efficiency is important.

Where only source of power is direct current at the lower voltage than desired output voltage, Switching regulators are only way which voltage can be generated.

In several power supplies there is need to use more than one regulating method in series and thus, output from the switching regulator can be further controlled by the linear regulator. Switching regulator accepts the wide range of input voltages and efficiently produces the voltage slightly above eventually desired output. Linear regulator which produces exactly the desired voltage and eliminates almost all noise produced by switching regulator follows switching regulator. This combination of regulating methods is called as Hybrid regulator.

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