POWER SUPPLY FILTER AND
REGULATOR
• A power supply filter ideally eliminates the fluctuations in the output
voltage of a halfwave or full-wave rectifier and produces a constant-
level dc voltage.
A voltage regulator prevents changes in the filtered dc voltage due to
variations in input voltage or load.
• The small amount of fluctuation in the filter output voltage is called
ripple.
• The filter is simply a capacitor connected from the rectifier output to
ground.
• When the input begins to decrease below its peak, the capacitor retains its charge
and the diode becomes reverse-biased. The capacitor can discharge only through
the load resistance at a rate determined by the RLC time constant . The larger the
time constant, the less the capacitor will discharge.
• the diode will again become forward-biased when the input voltage exceeds the
capacitor voltage by approximately 0.7 V.
• The variation in the capacitor voltage due to the charging and
discharging is called the ripple voltage.
• the full-wave rectified voltage has a smaller ripple than does a half-
wave voltage for the same load resistance and capacitor values.
• Ripple Factor : The ripple factor (r) is an indication of the effectiveness of the
filter and is defined as
𝑉𝑟(𝑝𝑝)
𝑟=
𝑉𝐷𝐶
Example
• Determine the ripple factor for the filtered bridge rectifier with a load
as indicated in the figure.
Voltage Regulators
• A voltage regulator is connected to the output of a filtered rectifier and
maintains a constant output voltage (or current) despite changes in the
input.
• Most regulators are integrated circuits
• The input to the regulator is first filtered with a capacitor to reduce the
ripple to <10%. The regulator reduces the ripple to a negligible
amount.
• Three-terminal regulators designed for fixed output voltages require
only external capacitors to complete the regulation portion of the
power supply.
Percent Regulation
• Line Regulation
It is typically defined as a ratio of a change in output voltage for a
corresponding change in the input voltage expressed as a percentage.
• Load Regulation The load regulation specifies how much change occurs in
the output voltage over a certain range of load current values, usually from
minimum current (no load, NL) to maximum current (full load, FL)
Example
• A certain 7805 regulator has a measured no-load output voltage of
5.18 V and a full-load output of 5.15 V. What is the load regulation
expressed as a percentage?
DIODE LIMITERS AND
CLAMPERS
Diode Limiters OR Clippers
Example
• What would you expect to see displayed on an oscilloscope
connected across RL in the limiter shown in the figure?
• Biased Limiters
THE END
Ahmed Abdelaleem
