Introduction to Half Wave Rectifier:
Half Wave Rectifier, Rectifier is a most fundamental and commonly used electronic circuit. Most of our electronic appliances consume D.C (Direct Current) power. Transmission of D.C over a long distance is very lossy. Moreover, DC Power can’t be stepped up or down as easily as AC.
To step up or step down AC, we can use transformers step-up or step-down which are freely designed and available. But same process can’t be used for DC. And generation of AC is more convenient. So globally most countries generate and transmit AC Power.
The property of AC is the polarity or direction of current changes every half cycle. The rapid changes in direction of current make AC not usable for digital appliances like smartphones, computers, and many such appliances.
In order to overcome this, we use a rectifier. In applications where DC Power is required while available power is AC in nature,we convert power using a Rectifier. Rectifier converts AC power to DC power. There are various type of Rectifiers based on their nature of operation, efficiency and components used.
Half Wave Rectifier (HWR) is one of most basic and primitive design. Its design is pretty simple but output power is not efficient. Power delivered at load is almost half of input power, that makes it undesirable for commercial use.
Circuit Diagram of Half Wave Rectifier:
Above figure shows circuit diagram for half wave rectifier, as seen it is very simple and uses very few components.
Step-Down Transformer is used in initial stage which steps-down or lowers input voltage to a desirable value. For example, consider a smartphone charger requires to deliver 5 V at output while power lines deliver 220/230 V AC. Output Voltage required is quite low as compared to AC mains so it should be lowered to desired range. Lowering the voltage decreases size of circuit, reduces size of components and makes device more safe for use.
The output of Step Down Transformer is fed to a diode. As all of us know diode’s operation is quite similar to operation of a switch. That it acts as a closed switched in forward bias and as a open switch in reverse bias. To attain forward bias, the voltage at Anode should be greater than the voltage or potential at cathode of diode. Similarly complete opposite conditions form reverse bias.
Operation of Half Wave Rectifier:
As from circuit its easy to understand operation of circuit. AC voltage consists of two half-cycles which together for a cycle. So if we evaluate the above circuit the conditions required to get the diode in forward bias will be achieved only in one of the two half cycles. Depending upon position of diode it will either conduct in positive half cycle or in negative half cycle. If the diode is placed as shown in above figure it will conduct in positive half cycle. If it is connected on lower wire/path it will conduct in negative half cycle.
Thus in which ever pattern diode is connected, it will only conduct in one half cycle, leading loss of half of the total power. That makes this circuit unfit for commercial use. To improve the design we can transform it using few components. And the modified circuit, Full Wave Rectifier can conduct in both half cycles. Thus making efficient use of power.