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Department of Electrical & Electronics Engineering, Amrita School of Engineering
Diode Applications
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Diode Application
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Diode Application
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Rectifiers
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Rectifiers
• The basic function of a Rectifier is to convert an AC voltage
to a pulsating DC voltage.
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Half-wave Rectifier
• Vout = (Vin – 0.7) V
• The average VDC or VAVG = Vp/
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Half-wave Rectifier
The output frequency is the
same as the input frequency.
fout = fin
PIV = Vpeak
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Full-wave Rectifier
• This method of rectification employs two diodes connected
to a center-tapped transformer.
• Full-wave signal has twice as many positive cycles as the
half-wave signal.
• Vout = (Vin – 0.7) V • The dc or average value VDC or VAVG = 2Vp/
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Full-wave Rectifier
• A full-wave output has twice as
many cycles as the sine-wave input.
• Frequency of the full-wave signal is
double the input frequency
fout = 2fin
PIV = 2Vpeak
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Bridge Rectifier
• Similar to full-wave rectifier as it produces a full-wave output
voltage
• The entire secondary voltage can be used
• Vout = (Vin – 1.4) V
• The dc or average value VDC or VAVG = 2Vp/
• Output frequency is double the input frequency
fout = 2fin
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Bridge Rectifier
PIV = Vpeak
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Filters
• The fluctuating or pulsating voltage from rectifier is
smoothened with a filter usually made of passive devices.
• Types of filters
• Choke-input filter
• Capacitive filter
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Choke-input filters
• Use inductor and capacitor as filters in the arrangement
shown below.
• The ac current in each component depends on the inductive
reactance, capacitive reactance, and the resistance.
• The choke (or inductor) has the primary characteristic of
opposing a change in current.
• A choke-input filter ideally reduces the ac current in the load
resistor to zero
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Choke-input filters
• Inductor has reactance given by
• Capacitor has reactance given by
• Design requirement – a well-designed choke-input filter
have XC at the input frequency much smaller than RL.
• When this condition is satisfied, load resistance is negligible
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Choke-input filters
• Second design requirement - a well-designed filter have XL
much greater than XC at the input frequency.
• When this condition is satisfied, the ac output voltage
approaches zero.
• Choke approximates a short circuit at 0 Hz and the capacitor
approximates an open at 0 Hz - the dc current can be
passed to the load resistance with minimum loss
• When XL is much greater than XC, almost all the ac voltage
is dropped across the choke.
• AC output voltage ,
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Choke-input filters
• All of the dc component is passed on to the load resistor,
and almost all of the ac component is blocked
• Output is not a perfect dc voltage but with a small ac load
voltage – ripple
• Advantages - Reduced ripples, Action is independent of load
current
• Disadvantages - Low output voltage, Bulky and large in size
The choke-input filter produces a dc output voltage
equal to the average value of the rectified voltage.
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Capacitor-input filters
• The capacitor-input filter produces a dc output voltage equal
to the peak value of the rectified voltage.
• Most widely used in power supplies
• Effect of Load Resistor - As long as the RLC time constant
is much greater than the period, the capacitor remains
almost fully charged and output is Vp.
Department of Electrical & Electronics Engineering, Amrita School of Engineering
Capacitor-input filters
• Peak-to-peak ripple voltage is,
VR - peak-to-peak ripple voltage, I - dc load current, f - ripple
frequency, C – capacitance