Test: L-Section Filter & CLC Filter - UPSC MCQ

 Given, V_L= 40V.
V_DC=2/π*V_L=2/π*40=25.46V.

LC=1/6√2ω²ϒ
ω=2πf=314
By putting the values, LC=1/6√2(314)² 0.02=40*10^-6.

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.

 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

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.

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_DCR.

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.

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.

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.

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.

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.

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.

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 / (LC₁C₂R_L) at 50Hz.

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.

We have, ϒ=5700 / (LC₁C₂R_L)
=5700 / (10*100*10^-12*3460)
=0.165%.

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.

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.

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.

 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.

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.