The document discusses filter circuits used in rectifiers to convert pulsating DC voltage into steady DC voltage by removing AC components called ripples. It covers various types of filters including shunt capacitor, series inductor, choke input, and capacitor input filters, detailing their advantages and disadvantages. The effectiveness of these filters is influenced by the values of the inductors and capacitors used.

1. FILTER CIRCUITS
G.PRASHANT

2. ● In a rectifier, a pulsating dc voltage is obtained by rectifying the ac
voltage, then filtering to a dc level and, finally, regulating to obtain a
desired fixed dc voltage.
FILTER CIRCUITS - INTRODUCTION

3. ● The output resulting from a rectifier is a pulsating dc
voltage.
● The smaller the AC variation with respect to the DC level, the better the
filter circuit operation.
FILTER CIRCUITS - INTRODUCTION

4. FILTER CIRCUITS - INTRODUCTION
● The output from the rectifier circuits is not purely DC, It also has some
AC components associated with it called ripples.
● A filter circuit is a device that converts the pulsating output of a rectifier
into a steady DC level.

5. ● A filter circuit is generally a combination of inductors L and capacitors
C.
● The filtering action of L and C depends on the facts an inductor only
allows DC and a capacitor allows AC only
● The values of L and C will determine the effective filtering out of the
AC components from the rectified output.
FILTER CIRCUITS - INTRODUCTION

6. FILTER CIRCUITS - FOR POWER SUPPLIES
● The most commonly used filter circuits
are :
1. Series inductor filter
2. Shunt capacitor filter
3. Choke input filter
4. Capacitor input

7. FILTER CIRCUITS - Shunt Capacitor Filter
● A high value capacitor C is placed in
parallel with the rectifier and the load
● The large value capacitor offers a low
impedance shunt path to the ripples
but offers high impedance to the DC
components.
● As we know, XC
= 1 / 2𝛑fC
● The ripple factor in capacitor filter is
given b

8. Full wave rectifier with Shunt
Capacitor
● In this case, capacitance C discharges twice during one cycle.
● Because both diodes conduct, non-conduction period is reduced
resulting in reduction in ripple voltage to half and DC voltage doubled
compared to
half-wave rectifier.

9. FILTER CIRCUITS - Shunt Capacitor Filter

10. Advantages
● Small size and weight
● Good characteristics
● Improved d.c. output
● Low cost
Disadvantages
● Capacitor draws more
current
FILTER CIRCUITS - Shunt Capacitor Filter

11. FILTER CIRCUITS - Series Inductor Filter
● A high value inductor or choke L
is connected in series with the
rectifier element and the load
● Thus the inductor offers a high
impedance to the AC components but
offers zero resistance to the desired DC
components, thereby removing ripples
● As we know, XL
= 2𝛑fL
● The ripple factor in series inductor filter

12. FILTER CIRCUITS - Choke Input Filter
● The inductor L allows DC to pass
but opposes AC
● Any remaining fluctuations are
largely bypassed by the shunt
capacitor
● Also known as L-section filter
● Ripple Factor = Vac rms/Vdc
= ( 2/3)(Xc/
√
XL)
= ( 2/3)(1/[2wc])(1/[2wL])
√
= 1/(6* 2*w^2*L*C)
√
● Salient features :

13. Advantages of Choke Filter or L-section Filter
1. It provides better voltage regulation.
2. The ripple factor can be varied according to the need.
Disadvantages of Choke Filter or L-Section filter
3. Bulky Size: These kinds of filters were popular in ancient time but it has
become obsolete now due to bulky size of inductors and capacitors.
4. Not suitable for low voltage power Supplies: These are not suitable for low
voltage power supplies. IC regulators or active filters are used in such
devices.
FILTER CIRCUITS - Choke Input Filter

14. FILTER CIRCUITS - Capacitor Input Filter
● Rectified output fed directly to a capacitor
C1
● Major part of filtering is done by C1
● The remaining ripple is removed by the
L-section filter consisting of an inductor L
and capacitor C2
● Also called 𝛑 filter
● Ripple Factor = 2/(8w3C1C2LRload)
√
● Salient features :
○ DC output voltage high
○ Voltage regulation PIV is high

15. Advantages of Pi filter (π- filter)
1. High Output Voltage
2. Low Ripple factor
3. High PIV
Disadvantage of Pi filter (π-
filter) Poor Voltage
Regulation
FILTER CIRCUITS - Capacitor Input Filter

16. THANK YOU