All the electronics circuits need a dc power supply of
required voltage for their operation.
To obtain this from the 230V ac mains supply we need to use
a rectifier. The rectified dc voltage is pulsating in nature.
therefore filters are used to obtain steady dc voltage.
The ripple or ac part in the rectified output is thus minimized
The filtered dc voltage is then applied to a regulator which will
try to keep the dc output voltage constant even if there is
mains voltage fluctuations.
• Filter: a circuit used to reduce the fluctuation in the rectified
output voltage or ripple. This provides a steadier dc voltage.
• Regulator: a circuit used to produces a constant dc output
voltage by reducing the ripple to negligible amount. One part of
Factors affecting the output voltage:
• The factors affecting the output voltage of a regulated power
1.Load current (IL) 2.input voltage (Vin)
A. Variation in output due to change in IL :
The output voltage of an unregulated power supply
reduces with increase in the load current,due to the voltage drops
across the secondary resistance.
B. Variation in output due to change in VIN :
As the output voltage of the unregulated power supply
changes with the change in ac i/p vol.,the regulator o/p also is likely to
change to some extent.
C. Variation in output due to change in temperature:
It takes place because the characteristics of the devices
used in the regulator ,filter circuit are temperature dependent.
Specifications of a voltage regulator :
Some of important parameters are:
1.Load regulation 2.Line regulation 3.Output resistance
4.Temperature stability factor 5.Ripple rejection
• Load regulation : Load regulation can be defined as the
percentage change in the output voltage from no-load (NL) to full-
load (FL).it should be as small as possible.
• Line regulation : Line regulation can be defined as the
percentage change in the output voltage for a given change in the
input voltage. it should be as small as possible.
• Output resistance should be low.
• Ripple rejection : it is the ability of the circuit to reject the ripple
in its input.
• Temperature stability factor: it should be low to prevent change in
output with the change in temperature.
VNL = the no-load output voltage
VFL = the full-load output voltage
Ripple rejection :
Ripple content in the output
Ripple content in the input
R.R.(dB) :20 log 10
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