Rectifier Circuit- Explained

    Making a rectifier circuit all by soldering yourself is a very easy job provided ones knows how to solder.The function of a rectifier is to convert alternating current into direct current. Here it is achieved by some popular and easily available circuit components like the diodes,capacitors,LM 78xx,led,resistor and relimates. Below is a list of components required:

• 5 DIODES (IN4007 for 1 amp)
• 1 SMALL PCB (DOT)
• 1 2500uF CAPACITOR
• 2 47uF CAPACITORS
• 1 LM 7805 (with heat sink)
• 1 0.1uF CAPACITOR
• 1 LED (any colour)
• 1 100Kilo-ohm RESISTOR
• SWITCH

 The circuit diagram looks similar to this schematic:

FIG.1- RECTIFIER SCHEMATIC (CLICK TO MAGNIFY)

   The diode arrangement (owing to its unilateral nature) converts the AC wave (fig.2,above) into a full rectified wave as in fig.2(below).

FIG.2-AC WAVE(ABOVE)
FULL RECTIFIED WAVE(BELOW)

 The capacitor(C1 &C2) gets charged during the first half of the crest when the voltage is rising from zero to a maximum . While the voltage again falls back to zero from the maximum the charged capacitor now discharges to maintain the voltage to the initial value. This process does not achieve a perfect straight line (fig.3) or a constant voltage at the output terminals, these small ripples are looked after by LM 7805, which itself is a fixed linear voltage regulator IC.

FIG.3-THE RESULTANT WAVE FORM FROM
THE CAPACITORS IS NOT FIXED/CONSTANT

 The IC is so designed to filter out ripples in the supply line and provide a fixed voltage as output. This fixed voltage is depicted in the IC name itself. The last two digits of the name signify the fixed voltage it produces as a output, the input to which is a voltage higher than that desired as output. In fact all members of the 78xx family does the same job, where 'xx' again represents the fixed output voltage it regulates the input to. In this case the fixed voltage being 5v depicted by '05' in the name '7805'. The IC with pin configuration is shown in fig.4.The first capacitor C1 is called the filter capacitor and is of 2500uF. Further lies the regulator. Another 47uF capacitor stabilizes the input. LM 7805 as mentioned earlier gives a perfect 5V output. The next lies the de-coupling capacitor (C3) of 47uF which in turn controls the voltage fluctuation if any. The last capacitor is a ceramic capacitor (C4) which protects the de-coupling capacitor from reverse polarization. When the circuit is in use the LED in series with a 100 kilo-ohm resistor lights up. The diode in the end prevents back flow of current which may arise during unexpected situations when in work.

FIG.4-LM7805 PIN
CONFIGURATION.

 The following table illustrates the input and out range of  LM7805. Care must be taken that the input does not exceed the given values :

LM 7805 INPUT AND OUTPUT RANGE

KEEP IN MIND

• While soldering first solder the components. After each component is soldered the ends extensions should be taken care by a wire stripper. If the soldering is good enough, even the fingers are enough to twist and detach the excess wire.
• The polarity of  electrolytic capacitors should be kept in mind.
• Female bugstrip should be used for LM7805. Refrain from soldering it directly to the PCB, the IC being sensitive would blow up.
• Do not forget to attach a heat sink to the IC, it gets really hot !!!
• Do not forget to insulate the copper face of the PCB after the soldering is completed, to avoid short circuiting and shocks. 

EXPERIENCE FIRST HAND  

Having made and used this circuit many a times, I feel that it is a good option for immediate use. Over a period of time the soldered lines begin to crack thus offering high resistance and thus limiting the current. Above this if the current passed is too high or high be the applied voltage leads to malfunction of the IC and may even blow off the capacitor (letting out yellowish mixture with a loud sound). Choosing a  line PCB, in which a whole line is shorted, will employ less soldering labour but the use of jumpers then becomes indispensable leading to a fragile circuit.