What is the need of using resistor in half wave rectifier?
It is not necessary to have a resistor in a half-wave rectifier. I think you are referring to the load resistance shown in the circuits. The idea behind the rectifier is to feed a DC load. charging in the real world can be any device running with direct current, such as a mobile phone, a laptop, etc. This load is represented as a simple resistor in the rectifier circuits to facilitate circuit analysis.
The resistance in the hwr circuit can or can not be used. there are no problems. but if we do not use any resistance in the circuit, the current will not flow or a very negligible amount of current will flow into the circuit.
in other words, the resistor acts as a load for the complete circuit and this amount of current will be absorbed by the source by the source.
Rectifiers are used to convert the AC signal into a continuous variable.
The resistance in the circuit is actually a load that requires a DC voltage for its operation.
the load can be resistive, inductive, capacitive.
For example, mobile chargers use an AC rectifier to convert alternating current into variable current. Since the DC output signal is variable, it is converted to pure DC using filters and voltage regulators, which gives a constant DC voltage. mobile. Likewise, rectifiers are used in motors for forward / reverse and braking. A motor forms an inductive load.
a half wave rectifier is usually a dirty and not expensive solution. except in very rare cases, it must not be used. this may be an appropriate solution when grinding a very small power or signal processing.
As it only corrects half of the wave, it creates a continuous superimposed current on the AC side. this current can bring a transformer on the AC side to saturation, causing very high currents on the primary side of the transformer, or even damage it if it is not protected against this type of load.
Even relatively small half-wave rectifiers can have this effect on larger transformers. you could cause a blackout in your neighborhood simply by using a half-wave rectification for a few kilowatts charge.
In addition to this side effect, there are a number of additional negative impacts on the AC circuit (on the motors, on the fault current switch, etc.)
that is why you should never rectify the half with larger loads.
Using a resistor parallel to the rectifier can help attenuate the DC current to a reasonable extent, at a cost (high) for overall efficiency.
the other uses of the resistors in the rectifiers (not only the half-wave rectifiers) serve to damp the high switching signals, but are then (in series with a capacitor) parallel to the diodes or parallel to the DC output (with a capacitor series). These well-proportioned resistors generate very little additional loss, usually less than 1%, or even less than 0.1%.
Finally, as others have said here, you may want to talk about the output resistance that means charging in some exponations of a half-wave rectifier. If this is the case, it is not part of the rectifier. It is simply put in the place of the load of a real application.