1.
What is rectifier?
A rectifier is an electrical device composed of one or more
diodes that converts alternating current (AC) to direct current (DC). A diode
is like a one-way valve that allows an electrical current to flow in only one
direction. This process is called rectification.
1.
2. Type of rectifiers
Rectifiers are
classified into a variety of configurations as shown in below figure. Depends
on factors like type of supply, bridge configuration, control nature,
components used, etc these rectifiers are classified. Majorly rectifiers are
classified into single phase and three phase rectifier and these are further
classified into uncontrolled, half controlled and full controlled rectifiers.
Let us see in brief about some of these types of rectifiers.
Single
Phase Uncontrolled RectifiersThis type of rectifiers uses the uncontrolled diode for
rectifying the input AC supply. At the output terminals of this rectifier,
power becomes constant and changes of its magnitude or value depend on load
requirement is not possible.
Half Wave Rectifier
It is a simple type of rectifier made with single diode which is
connected in series with load. For small power levels this type of rectifier
circuit is commonly used.During the positive half of the AC
input, diode becomes forward biased and currents starts flowing through it.
During the negative half of the AC input, diode becomes reverse biased and
current stops flowing through it. Output waveform across the load is shown in
figure. Because of high ripple content in the output, this type of rectifier is
seldom used with pure resistive load.
Full
Wave Center-tapped Rectifier
This type of rectifier uses two diodes and a transformer with
center tapped secondary winding. During the positive half cycle of the input AC
diode D1 is forward biased and the current starts flowing to the load through
it. During the negative half of the input diode D2 forward biased and D1
becomes reverse biased. Load current start flowing through D2 during this
negative peak. Note that the current flow through load has not changed even
when the voltage polarity changed.
Advantages of this rectifier are lower ripple factor and higher
efficiency, but the necessity of transformer with center tapping secondary is
the main disadvantage and makes a circuit as costlier.
1. 3. Rectifier
test and identify?
A rectifier is an
assembly of diodes that allows current in one direction only. There will be two
or three AC terminals and two DC terminals. Within the rectifier, there are two
diodes from each AC terminal—one to each DC terminal—that allow a flow of charge
toward the positive or away from the negative to create a DC output in the
correct direction.
Use a multimeter to
test each diode. First, shut down the turbine and disconnect the battery—be
sure to wait until the turbine is braked. Next, disconnect all of the wires
from the rectifier, taking care to identify them clearly for reconnection. Set
the multimeter to the diode test position, usually marked with a diode symbol.
Touching the meter
probes to each end of a diode will give three possible readings:
·
Open circuit (usually
indicated by a digit 1 on the left-hand side of the display, or the letters OL)
·
Diode forward voltage
(usually a number around 500 mV)
·
Short-circuit (usually
0.0)
A properly functioning
diode will give an asymmetrical outcome—open circuit one way and a forward
voltage the other way. A short-circuit or an open circuit in both directions
indicate a bad diode.
Place the red probe on
the positive DC terminal and check with the black probe on each of the AC
terminals in turn. You should see open circuit (top right photo). Now try
reversing the probes and place black on the positive DC. You should get a
number on the display each time you touch the red probe to an AC terminal.
Check the negative DC terminal in the same way and you should see the exact
opposite (bottom right photo).
If you find a shorted
diode or one that is open in both directions, the rectifier needs to be
replaced. Consider possible causes, including overcurrent, overheating from
poor connections, and lightning surges. Replacing your rectifier with one that
is made for higher voltage and current may prevent similar problems from
occurring in the future.
Application of rectifier?
The primary application of rectifiers is to
derive DC power from an AC supply (AC to DC converter). Virtually all
electronic devices require DC, so rectifiers are used inside the power supplies
of virtually all electronic equipment. Converting DC power from one voltage to
another is much more complicated. One method of DC-to-DC conversion first
converts power to AC (using a device called an inverter), then uses a
transformer to change the voltage, and finally rectifies power back to DC. A
frequency of typically several tens of kilohertz is used, as this requires much
smaller inductance than at lower frequencies and obviates the use of heavy,
bulky, and expensive iron-cored units. Rectifiers are also used for detection
of amplitude modulated radio signals. The signal may be amplified before
detection. If not, a very low voltage drop diode or a diode biased with a fixed
voltage must be used. When using a rectifier for demodulation the capacitor and
load resistance must be carefully matched: too low a capacitance makes the high
frequency carrier pass to the output, and too high makes the capacitor just
charge and stay charged. Rectifiers supply polarised voltage for welding. In
such circuits control of the output current is required; this is sometimes
achieved by replacing some of the diodes in a bridge rectifier with thyristors,
effectively diodes whose voltage output can be regulated by switching on and
off with phase fired controllers.
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