1. 2.8 CLIPPERS
A. Series clipper: The addition of a dc supply such as shown in Fig can have a pronounced effect on the on the anatysis of the series clipper configuration.
Take carful note of where the output voltage is defined.
Try to develop on overall sense of the response by each supply noting the “pressure “ established by each supply and the effect it will have on the conventional current direction through the diode.
Figure 2.25 Series clipper with a dc supply.
Any supply voltage greater than V volts will turn the diode on and conduction can be established through the load resistor. We can conclude that the diode will be on for any voltage Vi that is greater than V volts and OFF for any lesser voltage. For the “OFF” condition, the output would be 0V due the lack of current, and for the “ON” condition it would simply be
As determined by Kirchhoff’s voltage law.
3. Determine the applied voltage (transition voltage) that will result in change of state for the diode.
From the “OFF” to the “ON” state:

2. for the “off” region is an open circuit , ID = 0mA , VO = 0V.
For the “ON” region the diodes is replaced by short circuit equivalent and
Fig 2.26 Determining vo for the diode in the “ON” state.
for the “off” region is an open circuit , ID = 0mA , VO = 0V.
4. It is often helpful to draw the output waveform directly below the applied voltage using the same scales for the horisontal axis and the vertical axis.
For the “ON” conduction, output voltage has it’s peak value: VOpeak = Vm - V

3. B. Parallel Clipper:
The network of Fig is the simplest of parallel diode configurations with the output for the same inputs. The analysis of parallel configurations is very similar to that applied to series configurations.
Figure 2.27 Response to a parallel clipper.

4. EXAMPLE: Determine vo for the network of Fig. 2.28. Solution:
Figure 2.28
Solution:
Step-1. The output is defined across the series combination of the 4V- Supply and the diode, not across resistor R.
Step-2. The polarity of the dc supply and the direction of the diode strongly suggest that the diode will be in the “on” state for agood portion of the negative region of the input signal. In fact, It is interesting to note that since the outpu is directly across the series combination,
Figure 2.29 Determining the transition level for.

5. If we repeat the Example using a silicon diode with VK = 0.7V.
When the diode is in it’s short- circuit state the output voltage will be directly across the 4-V dc supply. Requiring that the output be fixed at 4V. In other words, when the diode is on the output will be 4V, other than that, when the diode is an open circuit, the current through the series network will be 0mA and the voltage drop across thr resistor will be 0V. That will result in VO ≈ Vi whenever the diode is OFF.
Step-3. The transition level of the input voltage can be found from Fig. 2.29, by substituting the short – circuit equivalent and remembering the diode current Id = 0 mA at the instant of transition. The result is a change in state when Vi = 4 V.
Step-4. The transition level is drawn along with Vo = 4V when the diode is on. For Vi ≥4V. Vo = Vi .
If we repeat the Example using a silicon diode with VK = 0.7V.
Solution: The transition voltage can be first be determined by applying the condition Id= 0A at Vd =VD = 0.7V and obtaining the network of Fig. (2. 30). Applying KVL around the output loop in the clockwise direction, we find that :
Vi + VK – V = 0
Vi = V - VK = 4V – 0.7 = 3.3V with Vi ˃ 3.3 V, the diode open and VO = Vi .
For Vi ˂ 3.3V, the diode “on” state
VO = 4V – 0.7 = 3.3V
Figure 2.30 Determining the transition level for the network of Fig
Figure 2.31

6. 2.9 CLAMPERS:
The clamping network is one that will “clamp” a signal to a different dc level. The network must have a capacitor, a diode, and a resistive element.
But it can also employ an independent dc supply to introduce an additional shift. The magnitude of R and C must be chosen such that the time constant RC is large enough to ensure that the voltage across the capacitor does not discharge significantly during the interval the diode is nonconducting. Throughout the analysis we will assume that for all practical purposes the capacitor will fully charge or discharge in five time constants.
Figure 2.32 Clamper.
The simplest of clamper network is provided in Fig.(2.32) . It is important to note that the capacitor is connected directly between input and output signals and the resistor and the diode are connected in parallel with the output signal.

7. In general, the following steps may be helpful when analyzing clamping networks:
Step-1.Start the analysis of clamping networks by considering that part of the input signal that will forward bias the diode.
Step-2. During the period that the diode is in the “on” state, assume that the capacitor will charge up instantaneously to a voltage level determined by the network.
Step-3. Assume that during the period when the diode is in the “off” state the capacitor will hold on to its established voltage level.
Step-4. Throughout the analysis maintain a continual awareness of the location and reference polarity for Vo to ensure that the proper levels for vo are obtained.
Step-5. Keep in mind the general rule that the total swing of the total output must match the swing of the input signal.
Example: Determine vo for the network of Fig for the input indicated.?
Figure 2.36 Applied signal and network for Example

8. Fig.(2.38) Reference setting circuitID
2.10 ZENER DIODES
Fig(2.37) reviews the approximate circuits for each region of a zener diode assuming the straight – line approximations of each break.
So how demonstrate a zener diode can be used to establish reference voltage levels and act as a protection device. The use of a zener diode as regulator will then be described to detail because it is one of its major areas of application. Aregulatr is a combination of elements designed to ensure that the output voltage of a supply remains fairly constant. VD
Fig.(2. 37) Approximate equivalent circuits for the zener diode in the three possible regions of applications
Example: Determine the reference voltages provided by the network of fig. (2.38) which uses a white LED (4V) to indicate power is on. What is the power delivered to the LED and to the 6 V Zener diode.
Fig.(2.38) Reference setting circuit

10. Zener diode as a regulator:
The basic configuration appears in fig. (2.39). The analysis is first for fixed quantities followed by a fixed supply voltage and a variable load, and finally a fixed load and avariable supply.
Figure 2.39 Basic Zener regulator
VI and RL fixed:
The applied dc voltage is fixed, as is the load resistor. The analysis can be broken into two steps:
Determine the state of the Zener diode by removing it from the network and calculating the voltage across the resulting open circuit.
(2 – 14)
If V ≥ VZ, the Zener diode is “on”
Figure 2.40 Determining the
state of the Zener diode.
If V ˂ VZ, the diode is “off”

11. The power dissipated by the Zener diode is determined by:
2. Substitute the appropriate equivalent circuit and solve for the desired unknowns.
For the network of Fig , the “on” state will result in the equivalent network of Fig Since voltages across parallel elements must be the same, we find that:
(2 - 15)
The Zener diode current must be determined by an application of Kirchhoff’s current law. That is,
(2 – 16)
The power dissipated by the Zener diode is determined by:
Figure 2.41 Substituting the
Zener equivalent for the “on” situation
(2 – 17)

12. Fixed Vi, Variable RL
Due to the offset voltage VZ, there is a specific range of resistor values (and therefore load current) which will ensure that the Zener is in the “on” state. Too small a load resistance RL will result in a voltage VL across the load resistor less than VZ , and the Zener device will be in the “off” state.
To determine the minimum load resistance of Fig that will turn the Zener diode on, simply calculate the value of RL that will result in a load voltage VL VZ. That is,
(2 – 18)
The condition defined by Eq. (2.20) establishes the minimum RL but in turn specifies the maximum IL as
(2 – 19)

13. Once the diode is in the “on” state, the voltage across R remains fixed at
(2 – 20)
and IR remains fixed at
(2 – 21)
The Zener current
(2 – 22)
resulting in a minimum IZ when IL is a maximum and a maximum IZ when IL is a minimum value since IR is constant.
Since IZ is limited to IZM as provided on the data sheet, it does affect the range of RL and therefore IL. Substituting IZM for IZ establishes the minimum IL as
(2 – 23)
and the maximum load resistance as
(2 – 24)

14. Fixed RL, Variable Vi
For fixed values of RL in Fig , the voltage Vi must be sufficiently large to turn the Zener diode on. The minimum turn-on voltage Vi Vimin is determined by
(2 – 25)
(2 – 26)
(2 – 27)

15. Figure 2.42 Sinusoidal ac regulation: 40-V peak-to-peak sinusoidal ac regulator