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AC to DC Conversion

Alternating Current is the current where the flow of electric current reverses the direction periodically while the flow of direct current happens in only one direction. The AC power is generally used in houses as well as in offices in running the electronic devices whereas the direct current is generally used in mobiles, flashlights and many electronic devices. Sometimes we need to convert the AC to DC to run many of the devices. Can we do so? Lets see how to do so using some simple electronic devices.

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AC to DC Conversion Theory

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Sometimes we need to convert AC power to DC one. Hence the rectification process has to be done. AC and DC converters are generally called as rectifiers and these rectify the waves by taking the waves which periodically reverses the direction  (AC) into dc current that flows in only one direction and the output waves are again freed from the ripples using the filters. Finally the regulators are used that maintains the constant voltage. Basically two rectifiers are well known one is half wave rectifier and the other is full wave rectifier. Half wave rectifier allows only half of the AC waveform to pass through the load resistance. Here only the half of the wave is only used as the output whereas full wave rectifier allows the whole wave and converts the entire wave in a single direction which increase the current wave capacity.
AC to DC Conversion Theory
AC to DC converter with power supply, transformer, rectifier, filter and regulator

We all know that the output voltage of the ac-dc converters using diodes is not controllable. It is because the diode is a self controlled switch. Turning on a diode depends on the polarity of the cathode voltage. Turning off depends on the polarity of the device current. Output voltage can be controlled if the diode can be replaced by the switch whose turning on and off can be controlled by a variable control voltage that is different from the anode to cathode voltage. Three terminal devices such as the thyristors, bipolar transistors and MOSFET's can be used as controllable switches. AC to DC conversion takes place if the power source in an ac supply and if the application is a dc load such as battery charging, dc motors, electrolysis, electromagnets, entertainment equipment and dc power supplies for computers etc. An important application is to provide a dc link between an ac source of one frequency and an ac load of a different frequency. 

AC to DC Conversion Formula

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The ac to dc converter converts the ac input into the dc output. Average power is transferred from an ac source to a dc load. The ac to dc converter is called as rectifier.The peak inverse voltage is the maximum reverse voltage to which the diode is subjected when it is non conducting. The rated PIV is specified by the manufacturer. 

If VRMS is the root mean square of the the given output voltage, VPeak is the peak input voltage of the phase, Vdc is the dc output voltage. The root mean square voltage VRMS is given by
VRMS = $\frac{V_{peak}}{2}$
The dc output voltage Vdc is given by
Vdc = $\frac{V_{peak}}{\pi}$
where Vpeak is the peak of the input phase voltage.

The Full wave rectifier formula has below formulas:
Peak current is given by
Ipeak = $\frac{V_{peak}}{R_L}$
Where V_peak is the peak voltage and RL isthe load resistance.
RMS voltage is given by
IRMS = $\frac{I_{peak}}{\sqrt{2}}$
Where IRMS is rms current and Ipeak is peak current
The AC to DC conversion factor is given by
AC = $\frac{DC}{0.636}$
Where AC is alternating current and DC is direct current.

AC to DC Conversion Methods

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In some of the applications such as domestic and laboratory environments, the portable instrument may be operating near an AC source so that these instruments are charged when necessary. Also, under normal operations it is better to use AC power instead of wasting battery energy. When main power is used, it is necessary to convert AC into DC form. There are many different AC to DC conversion methods with different types of circuit having almost the same electronic components, Here are some main components:
  1. Transformer, to reduce the AC to acceptable levels and isolate from power lines
  2. Rectifier, to convert AC to DC
  3. Filter, to minimize oe eliminate ripples after rectification
  4. Regulator to maintain a constant level of voltage against the fluctuations.

What Converts AC to DC?

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Rectifier is the device that converts alternating current (AC) to the direct current (DC).This flow happens in one direction only. A variety of diode configurations are used to convert AC into DC. The simple illustration is diode. Rectifiers are generally used in power supplies, detectors, transmission systems, laptops, video systems and televisions.There are basically three types of rectifiers:
  1. Half wave rectifier
  2. Full wave rectifier
  3. Bridge rectifier
Half Wave Rectifier: Its circuit consists of transformer where voltage is applied and a single diode in series with a resistance. In a half wave rectifier the negative half wave cycle of input voltage are cut off and the other positive half wave will be taken as the output. 

Half Wave Rectifier
Full Wave Rectifier: If two diodes are connected the conduction happens through one diode during the next half cycle a unidirectional current flows through the load resistance during the full cycle of the input voltage. Here we consider two positive half cycles that gives out the output in a single direction rather than reversing.
Bridge Rectifier: It consists of four diodes where only two diodes in the opposite arms of the bridge conduct simultaneously while other two diodes remain off as shown in circuit. The Diodes D1 and D3 conduct whereas the diodes D2 and D4 do not. Hence the current passes through the load resistance RL. Here the current is unidirectional and voltage is also unidirectional. It produces the output twice that of secondary voltage.

Resultant Output Waveform
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