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QUESTION: 1

An L section filter with L=2henry and C= 49µF is used in the output of a full wave single phase rectifier that is fed from a 40-0-40 V peak transformer. The load current is 0.2A. Calculate the output dc voltage.

Solution:

Given, V_{L}= 40V.

V_{DC}=2/π*V_{L}=2/π*40=25.46V.

QUESTION: 2

Calculate LC for a full wave rectifier which provides 10V dc at 100mA with a maximum ripple of 2%. Input ac frequency is 50Hz.

Solution:

LC=1/6√2ω^{2}ϒ

ω=2πf=314

By putting the values, LC=1/6√2(314)^{2} 0.02=40*10^{-6}.

QUESTION: 3

The value of inductance at which the current in a choke filter does not fall to zero is_________

Solution:

When the value of inductance is increased, a value is reached where the diodes supplies current continuously. This value of inductance is called critical inductance.

QUESTION: 4

The condition for the regulation curve in a choke filter is_________

Solution:

IDC should not exceed the negative peak of ac component. So, the regulation curve in direct output voltage against load current for a filter is given the relation LC≥R_{L}/3ω

QUESTION: 5

The ripple factor for an l section filter is_______

Solution:

The ripple factor is the ratio of root mean square (rms) value of ripple voltage to absolute value of dc component. It can also be expressed as the peak to peak value.

QUESTION: 6

The output dc voltage of an LC filter is_______

Solution:

The value for V_{DC} is same as that of inductor filter. If inductor has no dc resistance, then V_{DC}=2V_{m}/π. If R is the series resistance of transformer, then V_{DC}=2V_{m}/π – I_{DC}R.

QUESTION: 7

The rms value of ripple current for an L section filter is_______

Solution:

The ac current through L is determined primarily by X_{L}=2ωL. It is directly proportional to voltage produced and indirectly proportional to the reactance.

QUESTION: 8

What makes the load in a choke filter to bypass harmonic components?

Solution:

When the capacitor is shunted across the load, it bypasses the harmonic components. This is because it offers low reactance to ac ripple component. In another hand the inductor offers high impedance to harmonic terms.

QUESTION: 9

The ripple to heavy loads by a capacitor is_______

Solution:

Ripple factor is inversely proportional to load resistance for a capacitor filter.

So, the ripples that are produced are low when the load is high.

QUESTION: 10

In a choke l section filter_______

Solution:

The choke filter is sometimes also called as L section filter because the inductor and capacitor are connected in the shape ’L’ or inverted manner. But several sections of this choke filter are employed to smooth the output curve and make it free from ripples.

QUESTION: 11

What is the number of capacitors and inductors used in a CLC filter?

Solution:

A very smooth output can be obtained by a filter consisting of one inductor and two capacitors connected across each other. They are arranged in the form of letter ‘pi’. So, these are also called as pi filters.

QUESTION: 12

Major part of the filtering is done by the first capacitor in a CLC filter because _________

Solution:

The CLC filters are used when high voltage and low ripple frequency is needed than L section filters. The capacitor in a CLC filter offers very low reactance to the ripple frequency. So, maximum of the filtering is done by the first capacitor across the L section part.

QUESTION: 13

At f=50Hz, the ripple factor of CLC filter is_________

Solution:

The ripple factor of a rectifier is the measure of disturbances produced in the output. It’s the effectiveness of a power supply filter to reduce the ripple voltage. The ratio of ripple voltage to DC output voltage is ripple factor which is 5700 / (LC_{1}C_{2}R_{L}) at 50Hz.

QUESTION: 14

A single phase full wave rectifier makes use of pi section filter with 10µF capacitors and a choke of 10henry. The secondary voltage is 280V and the load current is 100mA. Determine the dc output voltage when f=50Hz.

Solution:

Given, V_{RMS}=280V

So, V¬m = 1.414*280=396V.

From theory of capacitor filter, V_{DC} = V_{m} –I_{DC}/4fC=396-0.1/ (4*50*10*10^{-6})=346V.

QUESTION: 15

For a given CLC filter, the operating frequency is 50Hz and 10µF capacitors used. The load resistance is 3460Ω with an inductance of 10henry. Calculate the ripple factor.

Solution:

We have, ϒ=5700 / (LC_{1}C_{2}R_{L})

=5700 / (10*100*10^{-12}*3460)

=0.165%.

QUESTION: 16

The inductor is placed in the L section filter because_________

Solution:

The inductor offers high reactance to ac component and zero resistance to dc component. So, it blocks the ac component which cannot be bypassed by the capacitors.

QUESTION: 17

The voltage in case of a full wave rectifier in a CLC filter is_________

Solution:

T he filter circuit is a combination of capacitors and inductors. The RMS value depends on the peak value of charging and discharging magnitude, V_{PEAK}.

QUESTION: 18

The advantages of a pi-filter is_________

Solution:

Due to the use of two capacitors with an inductor, an improved filtering action is provided. This leads to decrement in ripple factor. A low ripple factor signifies regulated and ripple free DC voltage.

QUESTION: 19

What is the relation between time constant and load resistance?

Solution:

If the load resistance value is large, the discharge time constant will be of a high value. Thus the capacitors time to discharge will get over soon. This lowers the amount of ripples in the output and increases the output voltage. If the load resistance is small, the discharge time constant will be more with decrease in output voltage.

QUESTION: 20

The output waveform of CLC filter is superimposed by a waveform referred to as_________

Solution:

Since the rectifier conducts current only in the forward direction, any energy discharged by the capacitor will flow into the load. This result in a DC voltage upon which is superimposed a waveform referred to as a saw tooth wave.

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