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Department of Electrical & Electronics Engineering, Amrita School of Engineering

Diode Applications


Diode Application


Diode Application


Rectifiers


Rectifiers

• The basic function of a Rectifier is to convert an AC voltage

to a pulsating DC voltage.


Half-wave Rectifier

• Vout = (Vin – 0.7) V

• The average VDC or VAVG = Vp/


Half-wave Rectifier

The output frequency is the

same as the input frequency.

fout = fin

PIV = Vpeak


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/


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


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


Bridge Rectifier

PIV = Vpeak


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


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


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


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 ,


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.


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.


Capacitor-input filters

• Peak-to-peak ripple voltage is,

VR - peak-to-peak ripple voltage, I - dc load current, f - ripple

frequency, C – capacitance

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Networked Embedded Systemseeeforum.weebly.com/uploads/1/0/2/5/10254481/15eee111_lec15.pdf · Diode Applications . Department of Electrical & Electronics Engineering, Amrita School