Module-1
Part-A
Block diagram of a d.c. power supply
The block diagram of a d.c. power supply is as shown in Fig. Since the mains input is at a
relatively high voltage, a step-down transformer of appropriate turns ratio is used to convert
this to a low voltage. The a.c. output from the transformer secondary is then rectified using
conventional silicon rectifier diodes to produce an unsmoothed (sometimes referred to as
pulsating d.c.) output. This is then smoothed and filtered before being applied to a circuit
which will regulate (or stabilize) the output voltage so that it remains relatively constant in
spite of variations in both load current and incoming mains voltage. Figure shows how some
of the electronic components that we have already met can be used in the realization of the
block diagram in Fig. The iron-cored step-down transformer feeds a rectifier arrangement
(often based on a bridge circuit). The output of the rectifier is then applied to a high-value
reservoir capacitor. This capacitor stores a considerable amount of charge and is being
constantly topped-up by the rectifier arrangement. The capacitor also helps to smooth out the
voltage pulses produced by the rectifier. Finally, a stabilizing circuit (often based on a series
transistor regulator and a zener diode voltage reference) provides a constant output voltage.
Rectifiers
They are the devices that transforms input AC to output DC. The component which converts
a sinusoidal AC signal waveform into single polarity half cycle is diode. One important
application of diode is rectification. Process of conversion of AC to DC is called rectification.
Any electrical instrument used for rectification provides a lesser resistance to the current in
__________________________________________________________________________________
Dr Raghunandan G H 1
, one direction but a much higher resistance to current in opposite direction is known as
rectifier.
The two types of rectifiers are
1. Half Wave Rectifier. 2. Full Wave Rectifier
Half Wave Rectifier
Fig.(a) Halfwave rectifier circuit (b) Halfwave rectifiers during positive half cycle (c) Half
wave rectifiers during negative half cycle
In almost all the rectifier circuits, transformers are generally used for following purposes.
i. Either to step up or step down the input voltage.
ii. To provide better isolation between AC supply and rectifier
circuit.
Operation: When AC input is given to primary of the transformer, it is mutually coupled
across secondary. During positive half cycle of Vi point A is positive, point b is negative.
Since anode is positive, diode is forward biased and acts as short circuit. Current flows
through RL and Vo follows the input.
Vo = Vm sin wt
__________________________________________________________________________________
Dr Raghunandan G H 2
Part-A
Block diagram of a d.c. power supply
The block diagram of a d.c. power supply is as shown in Fig. Since the mains input is at a
relatively high voltage, a step-down transformer of appropriate turns ratio is used to convert
this to a low voltage. The a.c. output from the transformer secondary is then rectified using
conventional silicon rectifier diodes to produce an unsmoothed (sometimes referred to as
pulsating d.c.) output. This is then smoothed and filtered before being applied to a circuit
which will regulate (or stabilize) the output voltage so that it remains relatively constant in
spite of variations in both load current and incoming mains voltage. Figure shows how some
of the electronic components that we have already met can be used in the realization of the
block diagram in Fig. The iron-cored step-down transformer feeds a rectifier arrangement
(often based on a bridge circuit). The output of the rectifier is then applied to a high-value
reservoir capacitor. This capacitor stores a considerable amount of charge and is being
constantly topped-up by the rectifier arrangement. The capacitor also helps to smooth out the
voltage pulses produced by the rectifier. Finally, a stabilizing circuit (often based on a series
transistor regulator and a zener diode voltage reference) provides a constant output voltage.
Rectifiers
They are the devices that transforms input AC to output DC. The component which converts
a sinusoidal AC signal waveform into single polarity half cycle is diode. One important
application of diode is rectification. Process of conversion of AC to DC is called rectification.
Any electrical instrument used for rectification provides a lesser resistance to the current in
__________________________________________________________________________________
Dr Raghunandan G H 1
, one direction but a much higher resistance to current in opposite direction is known as
rectifier.
The two types of rectifiers are
1. Half Wave Rectifier. 2. Full Wave Rectifier
Half Wave Rectifier
Fig.(a) Halfwave rectifier circuit (b) Halfwave rectifiers during positive half cycle (c) Half
wave rectifiers during negative half cycle
In almost all the rectifier circuits, transformers are generally used for following purposes.
i. Either to step up or step down the input voltage.
ii. To provide better isolation between AC supply and rectifier
circuit.
Operation: When AC input is given to primary of the transformer, it is mutually coupled
across secondary. During positive half cycle of Vi point A is positive, point b is negative.
Since anode is positive, diode is forward biased and acts as short circuit. Current flows
through RL and Vo follows the input.
Vo = Vm sin wt
__________________________________________________________________________________
Dr Raghunandan G H 2
