POWER SUPPLY

Rectifier .Types of Power Supply
There are many types of strength deliver. Most are designed to transform excessive voltage AC mains strength to a appropriate low voltage supply for electronics circuits and different devices. A energy deliver can by means of damaged down into a sequence of blocks, each of which performs a particular function.

For example a 5V regulated supply:

Block Diagram of a Regulated Power Supply System

 Transformer – steps down high voltage AC mains to low voltage AC.
• Rectifier – converts AC to DC, however the DC output is various.
• Smoothing – smooths the DC from varying significantly to a small ripple.
• Regulator – eliminates ripple by way of setting DC output to a fixed voltage.
Power supplies crafted from those blocks are described underneath with a circuit diagram and a graph of their output:Transformer only

AC power supply, transformer only

The low voltage AC output is suitable for lamps, heaters and unique AC motors. It isn’t always suitable for digital circuits except they include a rectifier and a smoothing capacitor.
See: Transformer


Transformer + Rectifier

DC power supply, transformer + rectifier

The varying DC output is suitable for lamps, warmers and standard motors. It is not suitable for electronic circuits unless they encompass a smoothing capacitor.See: Transformer | Rectifier


Transformer + Rectifier + Smoothing

Smooth DC power supply, transformer + rectifier + smoothing

The smooth DC output has a small ripple. It is suitable for most electronic circuits.

See: Transformer | Rectifier | Smoothing


Transformer + Rectifier + Smoothing + Regulator

Regulated DC power supply, transformer + rectifier + smoothing + regulator

The regulated DC output is very smooth with no ripple. It is suitable for all electronic circuits

Transformer

Transformers convert AC power from one voltage to another with little loss of power. Transformers work best with AC and this is one of the reasons why mains electricity is AC.
Step-up transformers growth voltage, step-down transformers reduce voltage. Most electricity resources use a step-down transformer to lessen the dangerously high mains voltage (230V in UK) to a more secure low voltage.
Transformers waste very little electricity so the electricity out is (nearly) same to the power in. Note that as voltage is stepped down modern-day is stepped up.Transformer, photograph © Rapid Electronics

The input coil is known as the primary and the output coil is called the secondary. There is no electrical connection between the two coils, instead they are linked by means of an alternating magnetic subject created inside the soft-iron center of the transformer. The lines within the center of the circuit image constitute the middle.Rapid Electronics: Transformers

transformer symbol

Transformer circuit symbol

Turns ratio
The ratio of the number of activates every coil, referred to as the turns ratio, determines the ratio of the voltages. A step-down transformer has a large wide variety of turns on its primary (input) coil that’s linked to the high voltage mains deliver, and a small number of activates its secondary (output) coil to offer a low output voltage.

Turns ratio = Vp = Np
Vs Ns
power out = electricity in
Vs × Is = Vp × Ip
Vp = number one (input) voltage
Np = variety of turns on number one coil
Ip = number one (enter) modern-day
Vs = secondary (output) voltage
Ns = number of turns on secondary coil
Is = secondary (output) cutting-edge


Rectifier

There are numerous methods of connecting diodes to make a rectifier to convert AC to DC. The bridge rectifier is the maximum essential and it produces full-wave various DC. A full-wave rectifier can also be crafted from just two diodes if a centre-tap transformer is used, but this technique is rarely used now that diodes are cheaper. A single diode can be used as a rectifier but it best uses the superb (+) elements of the AC wave to produce half of-wave varying DC.
Bridge rectifier
A bridge rectifier can be made the usage of four individual diodes, however it is also to be had in packages containing the four diodes required. It is referred to as a complete-wave rectifier due to the fact it makes use of all of the AC wave (both effective and terrible sections). Alternate pairs of diodes conduct, this modifications over the connections so the alternating directions of AC are converted to the one course of DC.
1.4V is used up in a bridge rectifier because there is 0.7V throughout each diode while undertaking and there are constantly diodes conducting, as shown in the diagram.
Bridge rectifiers are rated with the aid of the most modern they could skip and the maximum reverse voltage they are able to withstand. Their voltage rating need to be as a minimum three times the RMS voltage of the deliver so the rectifier can withstand the peak voltages. Please see the Diodes web page for greater details, including pictures of bridge rectifiers.

Operation of a Bridge Rectifier

Bridge rectifier

Full-wave Varying DC

Output: full-wave varying DC
(using all the AC wave)

Single diode rectifier

A unmarried diode can be used as a rectifier however this produces half-wave varying DC which has gaps when the AC is terrible. It is difficult to smooth this sufficiently well to deliver electronic circuits except they require a completely small present day so the smoothing capacitor does not drastically discharge at some stage in the gaps. Please see the Diodes web page for some examples of rectifier diodes..

Rapid Electronics: Rectifier diodes

Single diode rectifier

Single diode rectifier

Half-wave Varying DC

Output: half-wave varying DC
(using only half the AC wave)


Smoothing

Smoothing is executed with the aid of a big cost electrolytic capacitor connected throughout the DC deliver to act as a reservoir, supplying contemporary to the output whilst the various DC voltage from the rectifier is falling. The diagram indicates the unsmoothed various DC (dotted line) and the smoothed DC (solid line). The capacitor prices quickly near the height of the various DC, and then discharges because it supplies current to the outputSmoothing

Note that smoothing appreciably will increase the average DC voltage to almost the height price (1.4 × RMS cost). For example 6V RMS AC is rectified to complete wave DC of about 4.6V RMS (1.4V is lost inside the bridge rectifier), with smoothing this increases to nearly the peak value giving 1.4 × 4.6 = 6.4V easy DC.
Smoothing is not perfect because of the capacitor voltage falling a little because it discharges, giving a small ripple voltage. For many circuits a ripple that’s 10% of the deliver voltage is fine and the equation beneath gives the required value for the smoothing capacitor. A large capacitor will give less ripple. The capacitor price ought to be doubled when smoothing half-wave DC.
Rapid Electronics: Electrolytic Capacitors
Smoothing capacitor, C, for 10% ripple:

C = 5 × Io
Vs × f
where:
C = smoothing capacitance in farads (F)
Io = output cutting-edge in amps (A)
Vs = supply voltage in volts (V), that is the peak price of the unsmoothed DC
f = frequency of the AC deliver in hertz (Hz), this is 50Hz inside the UK.

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