Rectifiers I

This post consists all about RECTIFIERS.Here u'll get various exciting questions answers like HOW RECTIFIERS ARE USED TO MAKE REGULATED POWER SUPPLY USING VARIOUS COMPONENTS??WHAT THIS RMS VALUE EXACTLY MEAN??WHAT PARAMETRS SHOULD BE KEPT IN MIND WHILE DESIGNING A RECTIFIER?
Here u'll get TWO MORE EXTRA RECTIFIERS WITH THREE BASIC TYPES OF RECTIFIER,for knowing them keep on reading...

RECTIFIER:-   

An electrical device that converts an alternating current into a direct one by allowing a current to flow through it in one direction only.

The important point which is noticable in above definition is it's last three words "one direction only".Use any type of rectifier you will get current flow only in one direction.

Before proceeding further with amplifiers you should know what exactly RMS voltage value is and what is PEAK INVERSE VOLTAGE (PIV).

RMS (ROOT SQUARE MEAN) VOLTAGE:- 

In electronics, ac voltages typically are specified with a value equal to a dc voltage that is capable of doing the same amount of work. For sinusoidal voltages, this value is 0.707 times the peak voltage (Vo) and is called the root mean square or rms voltage (Vrms), given by

                                                       Vrms = (0.707)Vo

Household line voltages are specified according to rms values. This means that a 120-V ac line would actually have a peak voltage that is 1.414 times greater than the rms voltage.

PEAK INVERSE VOLTAGE (PIV) :-

The peak inverse voltage is the specified maximum voltage that a diode rectifier will block.

How to calculate this PIV for any factor will be discussed with the type of rectifier explanation.

TYPES OF RECTIFIER:-

So here comes the first type of rectifier named HALF WAVE RECTIFIER

I.HALF WAVE RECTIFIER:-

half wave rectifier

Assuming that input to all the types of amplifier is sinusoidal input.

The half-wave rectifier utilizes alternate half-cycles of the input sinusoid.For detailed study of half wave rectifier i'm removing diode D with it's battery-plus-resistance model.

equivqlent model of half wave rectifier

from this diagram we can write these equation 

                                                        vo = 0 if   vs < VDo         ...........(1)

             for another equation we can apply voltage divider rule across resistor R which results in

                                                      vo = R( vs - VDo)/(rD +R) ...............(2)

now may be the question arises in your mind  is how equation (1) comes so here's the answer of this question..

the model shown in above figure is PIECEWISE MODEL of DIODE.

about piecewise model of diode

from the above transfer characteristic graph equation 1 can be verified.

as rD is diode resistance so in comparison to load resistance it's very small so in eqn(2) 

                                          vo  nearly equal to ( vs - VDo)

where VDo= 0.7V or 0.8V 

OPERATION:- 

For positive half cycle of sinusoidal input the diode will be forward biased so it'll conduct and for negative half cycle it'll cut off n no conduction will take place.So it can be concluded that half wave rectifier conducts in positive half cycle.

the input and output of half wave rectifier is shown below:-

input and output waveform

 now,

In selecting diode for rectifier design two important parameter must be specified:-

1.THE CURRENT HANDLING CAPACITY that can be determined by the largest current the diode is expected to conduct.

2.THE PEAK INVERSE VOLTAGE (PIV) that the diode may be able to withstand without breakdown,determined by the largest reverse voltage that is expected to appear across the diode. 

PIV calculation:-
From the above definition it follows that the PIV is equal to the peak of  vs ,
                                                                       PIV = V,
It is usually prudent, however, to select a diode that has a reverse breakdown voltage at least
50% greater than the expected PIV.This circuit does not function properly when the input signal is small. For instance, this circuit cannot be used to rectify an input sinusoid of 100-mV amplitude. For such an application a special type of rectifier is required which we will discuss later.

OTHER RECTIFIERS EXPLANATION IS IN MY NEXT POST

 

Single Time Constant(STC) circuits

SINGLE TIME CONSTANT CIRCUITS:-

Study of these networks are important in designing of various amplifiers and filters which i'll discuss later.

An STC network is one that is composed of, or can be reduced to, one reactive component (inductance or capacitance) and one resistance. An STC network formed of an inductance L and a resistance R has a time constant T = L/R. The time constant T of an STC network composed of a capacitance C and a resistance R is given by T = CR.

Most of the STC networks can be classified in two categories:-
1.low pass network
2.high pass network

figures of both types of network are given below:-

(a)low pass network

 

(b)high pass network

 

the reason for such classification of STC networks is the reactance of a capacitor varies with frequency (Z = 1/jwC) it is easy to see that the transmission of
the circuit in Fig.(a) will decrease with frequency and approach zero as w approaches infinity.Thus the circuit of Fig.(a) acts as a low-pass filter;it passes low-frequency sine-wave inputs with little or no attenuation (at w = 0, the transmission is unity) and attenuates high-frequency input sinusoids. The circuit of Fig.(b) does the opposite; its transmission is unity at w = infinity  and decreases as w is reduced, reaching 0 for w=0.Therefore, this circuit performs as a high-pass filter.

for taking out FREQUENCY RESPONSE of these networks you can simply apply VOLTAGE DIVIDER RULE to their frequency domain equivalent network to find its OUTPUT VOLTAGE Vo and the results are shown in table.