HALF-WAVE RECTIFIER
Circuit Diagram:
o Transformer with primary and secondary coils
o Diode
o Load resistance RL
1. The AC voltage (to be rectified) is connected between the primary of
the transformer
2. Secondary of the transformer connected to the anode of the Diode
3. The output is measured across the load resistance RL
Input and output:
Working:
Case 1
During the positive half cycle of the input voltage, S1 becomes
positive and S2 becomes negative
Now Diode become forward biased (Resistance of the Diode
becomes low)
Hence, current flows in the circuit and we get output across the
load resistance RL
This is indicated in the graph above
Case 2
During the negative half cycle of the voltage, S1 becomes negative
and S2 becomes positive
Now Diode become Reverse biased (Resistance of the Diode
becomes High)
Hence, no current flows in the circuit and we do not get any output
across the load resistance RL
This is indicated in the graph above
The above process is repeated. we get only positive Hence, it is
called as Half-wave rectifier
The output signal is not continuous and available as bursts. Hence,
this is not of much use.
ADVANTAGE OF HALF WAVE RECTIFIER
Cheap (low number of components involved)
Simple
Easy to construct.( straight forwardness in circuit design.)
Disadvantages of Half Wave Rectifier
Only allow a half-cycle through per sine wave, and the other half-cycle is wasted. This
leads to power loss.
produces a low output voltage
The output current we obtain is not purely DC, and it still contains a lot of ripple (i.e. it
has a high ripple factor)
ADVANTAGE OF HALF WAVE RECTIFIER
Cheap (low number of components involved)
Simple
Easy to construct.( straight forwardness in circuit design.)
Disadvantages of Half Wave Rectifier
Only allow a half-cycle through per sine wave, and the other half-cycle is wasted. This
leads to power loss.
produces a low output voltage
The output current we obtain is not purely DC, and it still contains a lot of ripple (i.e. it
has a high ripple factor)
Advantages of full wave rectifier
High efficiency
Low ripple Factor
Disadvantages of full wave rectifier
Design is complicate
Need center tapped transformer
High cost
BRIDGE RECTIFIER
Many electronic circuits require a rectified DC power supply to power various
electronic basic components from the available AC mains supply. Rectifiers are
used to convert an AC power to a DC power. Compare HWR & FWR, BRIDGE
RECTIFIER is the most efficient rectifier circuit. BRIDGE RECTIFIERS as a type
of full-wave rectifier that uses four or more diodes.The bridge circuit configuration
efficiently convert alternating (AC) current to a direct (DC) current.
Construction
The construction of a bridge rectifier is shown in the figure below. The bridge
rectifier circuit is made of four diodes D1, D2, D3, D4, and a load resistor RL. The
four diodes are connected in a closed-loop configuration to efficiently convert the
alternating current (AC) into Direct Current (DC). The main advantage of this
configuration is the absence of the expensive center-tapped transformer. Therefore,
the size and cost are reduced.
The input signal is applied across terminals A and B and the output DC signal is
obtained across the load resistor RL connected between terminals C and D. The
four diodes are arranged in such a way that only two diodes conduct during each
half cycle. D1 and D3 are pairs that conduct during the positive half cycle/.
Likewise, diodes D2 and D4 conduct during a negative half cycle.
Working
When an AC signal is applied across the bridge rectifier, during the positive half
cycle, terminal A becomes positive while terminal B becomes negative. This
results in diodes D1 and D3 to become forward biased while D2 and D4 become
reverse biased
The current flow during the positive half-cycle is shown in the figure below:
During the NEGATIVE HALF-CYCLE, terminal B becomes positive while the
terminal A becomes negative. This causes diodes D2 and D4 to become forward
biased and diode D1 and D3 to be reverse biased.
The CURRENT FLOW DURING THE NEGATIVE HALF CYCLE is shown in the figure below:
From the figures given above, we notice that the current flow across load resistor
RL is the same during the positive half cycle and the negative half cycles. The
output DC signal polarity completely positive
Thus, a bridge rectifier allows electric current during both positive and negative
half cycles of the input AC signal.
The output waveforms of the bridge rectifier are shown in the below figure.
Advantages
The efficiency of the bridge rectifier is higher than the efficiency of a half-
wave rectifier. (efficiency of the bridge rectifier and full-wave rectifier is
same.)
The DC output signal of the bridge rectifier is smoother than the output DC
signal of a half-wave rectifier.
In a half-wave rectifier. Half of the input signal is wasted. However, in a
Bridge rectifier, output DC signal is almost equal to the input AC signal.
Disadvantages
The circuit of a bridge rectifier is complex when compared to a half-wave
rectifier and center-tapped full-wave rectifier
. Bridge rectifiers use 4 diodes while half-wave rectifiers use one Diode and
center tapped full wave rectifiers use only two diodes.
When more diodes are used more power loss occurs. In a center-tapped full-
wave rectifier, only one diode conducts during each half cycle. But in a
bridge rectifier, two diodes connected in series conduct during each half
cycle. Hence, the voltage drop is higher in a bridge rectifier.
DERIVATION IS SAME AS FULL WAVE RECTIFIER
