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Conversion of AC Supply to DC Supply

Updated on January 6, 2015

AC to DC conversion is the process of converting the alternating current (AC) to direct current (DC).

In general most of the electronic device requires the DC supply to perform their duties in circuits. The electronic devices or circuits are amplifiers, Oscillators, and other electronic equipments.

In practice dc power for electronic circuit is most conveniently obtain form AC lines by using the rectifier-filter-regulator, called a power supply.

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There are two types of power supply.

They are

  1. Linear mode power supply (LMPS):AC/DC power supply converter
  2. Switch mode power supply (SMPS): DC/DC power supply (converter) and DC/AC power supply (inverter)

Linear mode power supply (LMPS):

Transformer: Transformer is the static device which transfer the power from one circuit to another circuit

Transformers are two types:

  • Step up transformer
  • Step down transformer

Step up transformer:

In this transformer, primary winding has less number of turns when compare to secondary winding. So the primary voltage is less than the secondary.i.eN1<N2

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Step down transformer:

In this transformer, primary winding has more number of turns when compare to secondary winding. So the primary voltage is more than the secondary voltage. i.e. N1>N2

Rectifier:

Rectifier is defined as an electronic device used for converting ac voltage into unidirectional voltage

Rectifiers are classified into

1. Half wave rectifier

2. Full wave rectifier (centre tap)

3. Bridge rectifier

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Half wave rectifier:

It is the rectifier which converts the ac voltage into pulsating dc voltage using only one-half of the applied ac voltage because of the only one diode present in the circuit.

The components require for the half wave rectifier is one diode, transformer, load resistance.

Operation:

During the positive half cycle of the input signal the diode D is in forward bias that means the diode is conducting (closed switch). The entire positive half cycle output voltage appears across the load resistance.

During the negative half cycle of the input signal the diode D is in reverse bias that means the diode is not conducting (open switch). The entire negative half cycle output voltage appears across the load resistance is Zero volts.

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Full wave rectifier (center tapped):

In the full wave rectifier the currents flows through the load about both positive and negative half cycles and the components required for the circuit is, center tapped transformer, two P-N junction diodes, and load.

Operation:

During the positive half cycle of the input signal to the diode D1 in forward bias (conducts) and diode D2 in reverse bias then the entire positive half cycle output voltage from the diode D1 will appear across the load resistance.

During the negative half cycle of the input signal the Diode D1 in reverse bias and Diode D2 in forward bias (conducts) then the entire negative half cycle output voltage from the Diode D2 will appear across the load resistance.

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Bridge rectifier:

Full wave operation can be obtained even without the center tapped transformer in bridge rectifier. Bridge rectifier the components required they are four diodes D1, D2, D3, D4 are connected in the form of bridge and connected the load resistance across the supply voltage.

Operation:

During the positive half cycle of the input is given to the bridge rectifier then the diodes D1, D3 are in the forward bias(conducts) and Diodes D2, D4 are in the reverse bias then the entire positive half cycle output voltage appears across load resistance is obtained by the diodes D1, D3.

During the negative half cycle of the input signal from the supply then the DiodesD2, D4are in the forward bias (conducts)and diodes D3, D1 are in the reverse bias then the entire negative half cycle output voltage will appear across the load resistance by diodes D2,D4.

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Filter circuits:

Filter is the one of the electronic device which is used to remove the unwanted materials from the rectified output voltage. (it contains the ac and dc components) i.e we get the pure dc voltage from the filter circuit.

The ac component is undesirable and must be kept away from the load. The filter circuit is used to remove the ac component and to allow only the dc component to reach the load. Filter circuit should always kept the between the rectifier circuit and load

Types of filters:

They are four types of filters circuits they are:

1. Capacitor filter

2. Inductor filter

3. Capacitor and inductor filter (LC filter)

4. Capacitor inductor and capacitor (CLC filter)

Capacitor filter:

Capacitor is the one of the electronic device which is used to store the electrical energy in the form of electrical field

In the capacitor filter circuit, it consists of capacitor C which is connected across the rectifier output voltage. That is pulsating voltage from the rectifier circuit is applied across the capacitor.

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As we known the rectifier voltage increases to Vmax, at that time the capacitor fully charged. As the input voltage reaches peak value then the diode stops the conducting because of applied voltage of + Vmax at anode and voltage across the charge capacitor + Vmax at cathode. So the diode know act also open switch. Since the applied voltage slightly less than the Vmax the diode goes reverse bias then the output voltage stays at capacitors with the diode open switch the capacitor starts discharge through the load resistance the discharge time is constant for RLC circuit is much greater than the period of input signal.

Voltage regulator:

The output voltage form the filter circuits is not constant but varies with load when we applied to the voltage regulator we will get constant DC output voltage. The best example voltage regulator is zener diode because of the zener diode works in breakdown region as good condition.

In the circuit, the zener diode reversely connected across the load resistance should maintain output constant voltage. The series resistance absorbs the output voltage fluctuation.

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© 2015 KALYAN CHAKRAVARTHY THADAKA

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