CLIPPERS:
CLAMPER:
Clamping networks have a capacitor connected directly from input to output with a resistive element in parallel with the output signal. The diode is also parallel with the output signal but may or may not have a series dc supply as an added element.
Clippers are network that employ diodes to “clip” away a portion of an input signal
without distorting remaining part of the applied waveform. Depending on the
orientation of the diode, the positive or negative region the input signal is “clipped”
off. There are two categories of clippers: series and parallel The series configuration
is defined as one where the diode is in series with the load, while the parallel variety
has the diode in a parallel to the load.
Clamping networks have a capacitor connected directly from input to output with a resistive element in parallel with the output signal. The diode is also parallel with the output signal but may or may not have a series dc supply as an added element.
If the DC value of a signal needs to be changed, a capacitor can be charged with the appropriate
value. When connected in series with the signal source, it will then provide the desired DC level.
For positive values of the input signal, the diode immediately conducts, allowing the capacitor to be charged. The RC time constant is small because the only resistor present is the small internal resistor of the diode (less than 1 ). For negative values of the input signal, the diode is reverse-biased, so the capacitor cannot be discharged, maintaining the potential. In general, if we use a battery of voltage V , the output signal will be: Vout = −Vp + V + Vp sinwt = Vp(sinwt − 1) + V
In Fig: the diode characteristics are placed on the same set of axes as a straight line defined by the parameters of the network . The straight line is called a load line because the intersection on the vertical axis is defined by the applied load R. The analysis to follow is therefore called load-line analysis . The intersection of the two curves will define the solution for the network and define the current and voltage level for the network.
The polarity of Vd and the direction of Id clearly reveal that the diode is indeed in the forward-bios state, resulting in a voltage across the diode in the neighborhood of 0.7 V and a current on the order of 10mA or more .
The intersection of the load line on the characteristics of Fig: can be determined by applying KVL in the clockwise direction, which result is
+E –VD – Vr = 0
E = v D + ID R ………………(1)
If we set vD=0v in eq (1) and solve for ID .we have the magnitude of ID on the vertical axis.
Therefore with vD=0 v Eq 1 becomes
E = v D + ID R =0v+ ID R ………….(2)
And , ID =(E/R) vD=0 v as shown in fig If we set ID =0A in eq 2 and solve for vD we have the
magnitude of vD on the horizontal axis Therefore, with ID = 0 A,
Eq 2 becomes E = v D + ID R= v
D +(0A)R v D = E/ ID =0
Definition : A properly doped crystal diode which has a sharp breakdown voltage is known as
a zener diode.
When the reverse bias on a crystal diode is increased , a critical voltage , called breakdown voltage
is reached where the reverse current increase sharply to a high value . This breakdown voltage is
sometimes called zener voltage and the sudden increase in current is known as zener current.
The zener voltage depends upon the amount of doping . If the diode is heavily doped , depletion
layer will be thin and consequently the breakdown of the junction will occur at a lower reverse
voltage . On the other hand, a lightly doped diode has a higher breakdown voltage.
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