Category: electronic Circuits

Electronic Circuits – SMPS The topics discussed till now represent different sections of power supply unit. All these sections together make the Linear Power Supply. This is the conventional method of obtaining DC out of the input AC supply. Linear Power Supply The Linear Power Supply (LPS) is the regulated power supply which dissipates much heat in the series resistor to regulate the output voltage which has low ripple and low noise. This LPS has many applications. A linear power supply requires larger semiconductor devices to regulate the output voltage and generates more heat resulting in lower energy efficiency. Linear power supplies have transient response times up to 100 times faster than the others, which is very important in certain specialized areas. Advantages of LPS The power supply is continuous. The circuitry is simple. These are reliable systems. This system dynamically responds to load changes. The circuit resistances are changed to regulate the output voltage. As the components operate in linear region, the noise is low. The ripple is very low in the output voltage. Disadvantages of LPS The transformers used are heavier and large. The heat dissipation is more. The efficiency of linear power supply is 40 to 50% Power is wasted in the form of heat in LPS circuits. Single output voltage is obtained. We have already gone through different parts of a Linear Power supply. The block diagram of a Linear Power Supply is as shown in the following figure. In spite of the above disadvantages, Linear Power Supplies are widely used in low-noise amplifiers, test equipment, control circuits. In addition, they are also used in data acquisition and signal processing. All the power supply systems that needs simple regulation and where efficiency is not a concern, the LPS circuits are used. As the electrical noise is lower, the LPS is used in powering sensitive analog circuitry. But to overcome the disadvantages of Linear Power Supply system, the Switched Mode Power Supply (SMPS) is used. Switched Mode Power Supply (SMPS) The disadvantages of LPS such as lower efficiency, the need for large value of capacitors to reduce ripples and heavy and costly transformers etc. are overcome by the implementation of Switched Mode Power Supplies. The working of SMPS is simply understood by knowing that the transistor used in LPS is used to control the voltage drop while the transistor in SMPS is used as a controlled switch. Working The working of SMPS can be understood by the following figure. Let us try to understand what happens at each stage of SMPS circuit. Input Stage The AC input supply signal 50 Hz is given directly to the rectifier and filter circuit combination without using any transformer. This output will have many variations and the capacitance value of the capacitor should be higher to handle the input fluctuations. This unregulated dc is given to the central switching section of SMPS. Switching Section A fast switching device such as a Power transistor or a MOSFET is employed in this section, which switches ON and OFF according to the variations and this output is given to the primary of the transformer present in this section. The transformer used here are much smaller and lighter ones unlike the ones used for 60 Hz supply. These are much efficient and hence the power conversion ratio is higher. Output Stage The output signal from the switching section is again rectified and filtered, to get the required DC voltage. This is a regulated output voltage which is then given to the control circuit, which is a feedback circuit. The final output is obtained after considering the feedback signal. Control Unit This unit is the feedback circuit which has many sections. Let us have a clear understanding about this from The following figure. The above figure explains the inner parts of a control unit. The output sensor senses the signal and joins it to the control unit. The signal is isolated from the other section so that any sudden spikes should not affect the circuitry. A reference voltage is given as one input along with the signal to the error amplifier which is a comparator that compares the signal with the required signal level. By controlling the chopping frequency the final voltage level is maintained. This is controlled by comparing the inputs given to the error amplifier, whose output helps to decide whether to increase or decrease the chopping frequency. The PWM oscillator produces a standard PWM wave fixed frequency. We can get a better idea on the complete functioning of SMPS by having a look at the following figure. The SMPS is mostly used where switching of voltages is not at all a problem and where efficiency of the system really matters. There are few points which are to be noted regarding SMPS. They are SMPS circuit is operated by switching and hence the voltages vary continuously. The switching device is operated in saturation or cut off mode. The output voltage is controlled by the switching time of the feedback circuitry. Switching time is adjusted by adjusting the duty cycle. The efficiency of SMPS is high because, instead of dissipating excess power as heat, it continuously switches its input to control the output. Disadvantages There are few disadvantages in SMPS, such as The noise is present due to high frequency switching. The circuit is complex. It produces electromagnetic interference. Advantages The advantages of SMPS include, The efficiency is as high as 80 to 90% Less heat generation; less power wastage. Reduced harmonic feedback into the supply mains. The device is compact and small in size. The manufacturing cost is reduced. Provision for providing the required number of voltages. Applications There are many applications of SMPS. They are used in the motherboard of computers, mobile phone chargers, HVDC measurements, battery chargers, central power distribution, motor vehicles, consumer electronics, laptops, security systems, space stations, etc. Types of SMPS SMPS is the Switched Mode Power Supply circuit which is designed for obtaining the regulated DC output voltage

Electronic Circuits – Regulators The next and the last stage before load, in a power supply system is the Regulator part. Let us now try to understand what a regulator is and what it does. The part of electronics that deal with the control and conversion of electric power can be termed as Power Electronics. A regulator is an important device when it comes to power electronics as it controls the power output. Need for a Regulator For a Power supply to produce a constant output voltage, irrespective of the input voltage variations or the load current variations, there is a need for a voltage regulator. A voltage regulator is such a device that maintains constant output voltage, instead of any kind of fluctuations in the input voltage being applied or any variations in current, drawn by the load. The following image gives an idea of what a practical regulator looks like. Types of Regulators Regulators can be classified into different categories, depending upon their working and type of connection. Depending upon the type of regulation, the regulators are mainly divided into two types namely, line and load regulators. Line Regulator − The regulator which regulates the output voltage to be constant, in spite of input line variations, it is called as Line regulator. Load Regulator − The regulator which regulates the output voltage to be constant, in spite of the variations in load at the output, it is called as Load regulator. Depending upon the type of connection, there are two type of voltage regulators. They are Series voltage regulator Shunt voltage regulator The arrangement of them in a circuit will be just as in the following figures. Let us have a look at other important regulator types. Zener Voltage Regulator A Zener voltage regulator is one which uses Zener diode for regulating the output voltage. We have already discussed the details regarding Zener diode in BASIC ELECTRONICS tutorial. When the Zener diode is operated in the breakdown or Zener region, the voltage across it is substantially constant for a large change of current through it. This characteristic makes Zener diode a good voltage regulator. The following figure shows an image of a simple Zener regulator. The applied input voltage $V_i$ when increased beyond the Zener voltage $V_z$, then the Zener diode operates in the breakdown region and maintains constant voltage across the load. The series limiting resistor $R_s$ limits the input current. Working of Zener Voltage Regulator The Zener diode maintains the voltage across it constant in spite of load variations and input voltage fluctuations. Hence we can consider 4 cases to understand the working of a Zener voltage regulator. Case 1 − If the load current $I_L$ increases, then the current through the Zener diode $I_Z$ decreases in order to maintain the current through the series resistor $R_S$ constant. The output voltage Vo depends upon the input voltage Vi and voltage across the series resistor $R_S$. This is can be written as $$V_o=V_{in}-IR_{s}$$ Where $I$ is constant. Therefore, $V_o$ also remains constant. Case 2 − If the load current $I_L$ decreases, then the current through the Zener diode $I_Z$ increases, as the current $I_S$ through RS series resistor remains constant. Though the current $I_Z$ through Zener diode increases it maintains a constant output voltage $V_Z$, which maintains the load voltage constant. Case 3 − If the input voltage $V_i$ increases, then the current $I_S$ through the series resistor RS increases. This increases the voltage drop across the resistor, i.e. $V_S$ increases. Though the current through Zener diode $I_Z$ increases with this, the voltage across Zener diode $V_Z$ remains constant, keeping the output load voltage constant. Case 4 − If the input voltage decreases, the current through the series resistor decreases which makes the current through Zener diode $I_Z$ decreases. But the Zener diode maintains output voltage constant due to its property. Limitations of Zener Voltage Regulator There are a few limitations for a Zener voltage regulator. They are − It is less efficient for heavy load currents. The Zener impedance slightly affects the output voltage. Hence a Zener voltage regulator is considered effective for low voltage applications. Now, let us go through the other types of voltage regulators, which are made using transistors. Transistor Series Voltage Regulator This regulator has a transistor in series to the Zener regulator and both in parallel to the load. The transistor works as a variable resistor regulating its collector emitter voltage in order to maintain the output voltage constant. The figure below shows the transistor series voltage regulator. With the input operating conditions, the current through the base of the transistor changes. This effects the voltage across the base emitter junction of the transistor $V_{BE}$. The output voltage is maintained by the Zener voltage $V_Z$ which is constant. As both of them are maintained equal, any change in the input supply is indicated by the change in emitter base voltage $V_{BE}$. Hence the output voltage Vo can be understood as $$V_O=V_Z+V_{BE}$$ Working of Transistor Series Voltage Regulator The working of a series voltage regulator shall be considered for input and load variations. If the input voltage is increased, the output voltage also increases. But this in turn makes the voltage across the collector base junction $V_{BE}$ to decrease, as the Zener voltage $V_Z$ remains constant. The conduction decreases as the resistance across emitter collector region increases. This further increases the voltage across collector emitter junction VCE thus reducing the output voltage $V_O$. This will be similar when the input voltage decreases. When the load changes occur, which means if the resistance of the load decreases, increasing the load current $I_L$, the output voltage $V_O$ decreases, increasing the emitter base voltage $V_{BE}$. With the increase in the emitter base voltage $V_{BE}$ the conduction increases reducing the emitter collector resistance. This in turn increases the input current which compensates the decrease in the load resistance. This will be similar when the load current increases. Limitations of Transistor Series Voltage Regulator Transistor Series

Electronic Circuits – Signals A Signal can be understood as “a representation that gives some information about the data present at the source from which it is produced.” This is usually time varying. Hence, a signal can be a source of energy which transmits some information. This can easily be represented on a graph. Examples An alarm gives a signal that it’s time. A cooker whistle confirms that the food is cooked. A red light signals some danger. A traffic signal indicates your move. A phone rings signaling a call for you. A signal can be of any type that conveys some information. This signal produced from an electronic equipment, is called as Electronic Signal or Electrical Signal. These are generally time variants. Types of Signals Signals can be classified either as Analog or Digital, depending upon their characteristics. Analog and Digital signals can be further classified, as shown in the following image. Analog Signal A continuous time-varying signal, which represents a time-varying quantity, can be termed as an Analog Signal. This signal keeps on varying with respect to time, according to the instantaneous values of the quantity, which represents it. Digital Signal A signal which is discrete in nature or which is non-continuous in form can be termed as a Digital signal. This signal has individual values, denoted separately, which are not based on previous values, as if they are derived at that particular instant of time. Periodic Signal & Aperiodic Signal Any analog or digital signal, that repeats its pattern over a period of time, is called as a Periodic Signal. This signal has its pattern continued repeatedly and is easy to be assumed or to be calculated. Any analog or digital signal, that doesn’t repeat its pattern over a period of time, is called as Aperiodic Signal. This signal has its pattern continued but the pattern is not repeated and is not so easy to be assumed or to be calculated. Signals & Notations Among the Periodic Signals, the most commonly used signals are Sine wave, Cosine wave, Triangular waveform, Square wave, Rectangular wave, Saw-tooth waveform, Pulse waveform or pulse train etc. let us have a look at those waveforms. Unit Step Signal The unit step signal has the value of one unit from its origin to one unit on the X-axis. This is mostly used as a test signal. The image of unit step signal is shown below. The unit step function is denoted by $uleft ( t right )$. It is defined as − $$uleft ( t right )=left{begin{matrix}1 & tgeq 0\ 0 & t Unit Impulse Signal The unit impulse signal has the value of one unit at its origin. Its area is one unit. The image of unit impulse signal is shown below. The unit impulse function is denoted by ẟ(t). It is defined as $$delta left ( t right )=left{begin{matrix} infty ::if ::t=0\0 ::if ::tneq 0end{matrix}right.$$ $$int_{-infty }^{infty }delta left ( t right )dleft ( t right )=1$$ $$int_{-infty }^{t }delta left ( t right )dleft ( t right )=uleft ( t right )$$ $$delta left ( t right )=frac{duleft ( t right )}{dleft ( t right )} $$ Unit Ramp Signal The unit ramp signal has its value increasing exponentially from its origin. The image of unit ramp signal is shown below. The unit ramp function is denoted by u(t). It is defined as − $$int_{0}^{t}uleft ( t right ) dleft ( t right )=int_{0}^{t} 1 dt =t=rleft ( t right )$$ $$uleft ( t right )=frac{drleft ( t right )}{dt}$$ Unit Parabolic Signal The unit parabolic signal has its value altering like a parabola at its origin. The image of unit parabolic signal is shown below. The unit parabolic function is denoted by $uleft ( t right )$. It is defined as − $$int_{0}^{t}int_{0}^{t}uleft ( t right )dtdt=int_{0}^{t}rleft ( t right )dt=int_{0}^{t} t.dt=frac{t^{2}}{2}dt=xleft ( t right )$$ $$rleft ( t right )=frac{dxleft ( t right )}{dt}$$ $$uleft ( t right )=frac{d^{2}xleft ( t right )}{dt^{2}}$$ Signum Function The Signum function has its value equally distributed in both positive and negative planes from its origin. The image of Signum function is shown below. The Signum function is denoted by sgn(t). It is defined as $$sgnleft ( t right )=left{begin{matrix} 1 :: for :: tgeq 0\-1 :: for ::t $$sgnleft ( t right )=2uleft ( t right ) -1$$ Exponential Signal The exponential signal has its value varying exponentially from its origin. The exponential function is in the form of − $$xleft ( t right ) =e^{alpha t}$$ The shape of exponential can be defined by $alpha$. This function can be understood in 3 cases Case 1 − If $alpha = 0rightarrow xleft ( t right )=e^{0}=1$ Case 2 − If $alpha decaying exponential. Case 3 − If $alpha > 0$ then $xleft ( t right )=e^{alpha t}$ where $alpha$ is positive. This shape is called as raising exponential. Rectangular Signal The rectangular signal has its value distributed in rectangular shape in both positive and negative planes from its origin. The image of rectangular signal is shown below. The rectangular function is denoted by $xleft ( t right )$. It is defined as $$xleft ( t right )=A :rectleft [ frac{t}{T} right ]$$ Triangular Signal The rectangular signal has its value distributed in triangular shape in both positive and negative planes from its origin. The image of triangular signal is shown below. The triangular function is denoted by$xleft ( t right )$. It is defined as $$xleft ( t right )=A left [ 1-frac{left | t right |}{T} right ]$$ Sinusoidal Signal The Sinusoidal signal has its value varying sinusoidally from its origin. The image of Sinusoidal signal is shown below. The sinusoidal function is denoted by x (t). It is defined as − $$xleft ( t right )=A cos left ( w_{0} tpm phi right )$$ or $$xleft ( t right )=A sinleft ( w_{0}tpm phi right )$$ Where $T_{0}=frac{2 pi}{w_{0}}$ Sinc Function The Sinc signal has its value varying

Electronic Circuits – Full Wave Rectifiers A Rectifier circuit that rectifies both the positive and negative half cycles can be termed as a full wave rectifier as it rectifies the complete cycle. The construction of a full wave rectifier can be made in two types. They are Center-tapped Full wave rectifier Bridge full wave rectifier Both of them have their advantages and disadvantages. Let us now go through both of their construction and working along with their waveforms to know which one is better and why. Center-tapped Full-Wave Rectifier A rectifier circuit whose transformer secondary is tapped to get the desired output voltage, using two diodes alternatively, to rectify the complete cycle is called as a Center-tapped Full wave rectifier circuit. The transformer is center tapped here unlike the other cases. The features of a center-tapping transformer are − The tapping is done by drawing a lead at the mid-point on the secondary winding. This winding is split into two equal halves by doing so. The voltage at the tapped mid-point is zero. This forms a neutral point. The center tapping provides two separate output voltages which are equal in magnitude but opposite in polarity to each other. A number of tapings can be drawn out to obtain different levels of voltages. The center-tapped transformer with two rectifier diodes is used in the construction of a Center-tapped full wave rectifier. The circuit diagram of a center tapped full wave rectifier is as shown below. Working of a CT- FWR The working of a center-tapped full wave rectifier can be understood by the above figure. When the positive half cycle of the input voltage is applied, the point M at the transformer secondary becomes positive with respect to the point N. This makes the diode $D_1$forward biased. Hence current $i_1$ flows through the load resistor from A to B. We now have the positive half cycles in the output When the negative half cycle of the input voltage is applied, the point M at the transformer secondary becomes negative with respect to the point N. This makes the diode $D_2$ forward biased. Hence current $i_2$ flows through the load resistor from A to B. We now have the positive half cycles in the output, even during the negative half cycles of the input. Waveforms of CT FWR The input and output waveforms of the center-tapped full wave rectifier are as follows. From the above figure it is evident that the output is obtained for both the positive and negative half cycles. It is also observed that the output across the load resistor is in the same direction for both the half cycles. Peak Inverse Voltage As the maximum voltage across half secondary winding is $V_m$, the whole of the secondary voltage appears across the non-conducting diode. Hence the peak inverse voltage is twice the maximum voltage across the half-secondary winding, i.e. $$PIV=2V_m$$ Disadvantages There are few disadvantages for a center-tapped full wave rectifier such as − Location of center-tapping is difficult The dc output voltage is small PIV of the diodes should be high The next kind of full wave rectifier circuit is the Bridge Full wave rectifier circuit. Bridge Full-Wave Rectifier This is such a full wave rectifier circuit which utilizes four diodes connected in bridge form so as not only to produce the output during the full cycle of input, but also to eliminate the disadvantages of the center-tapped full wave rectifier circuit. There is no need of any center-tapping of the transformer in this circuit. Four diodes called $D_1$, $D_2$, $D_3$ and $D_4$ are used in constructing a bridge type network so that two of the diodes conduct for one half cycle and two conduct for the other half cycle of the input supply. The circuit of a bridge full wave rectifier is as shown in the following figure. Working of a Bridge Full-Wave Rectifier The full wave rectifier with four diodes connected in bridge circuit is employed to get a better full wave output response. When the positive half cycle of the input supply is given, point P becomes positive with respect to the point Q. This makes the diode $D_1$ and $D_3$ forward biased while $D_2$ and $D_4$ reverse biased. These two diodes will now be in series with the load resistor. The following figure indicates this along with the conventional current flow in the circuit. Hence the diodes $D_1$ and $D_3$ conduct during the positive half cycle of the input supply to produce the output along the load resistor. As two diodes work in order to produce the output, the voltage will be twice the output voltage of the center tapped full wave rectifier. When the negative half cycle of the input supply is given, point P becomes negative with respect to the point Q. This makes the diode $D_1$ and $D_3$ reverse biased while $D_2$ and $D_4$ forward biased. These two diodes will now be in series with the load resistor. The following figure indicates this along with the conventional current flow in the circuit. Hence the diodes $D_{2}$ and $D_{4}$ conduct during the negative half cycle of the input supply to produce the output along the load resistor. Here also two diodes work to produce the output voltage. The current flows in the same direction as during the positive half cycle of the input. Waveforms of Bridge FWR The input and output waveforms of the center-tapped full wave rectifier are as follows. From the above figure, it is evident that the output is obtained for both the positive and negative half cycles. It is also observed that the output across the load resistor is in the same direction for both the half cycles. Peak Inverse Voltage Whenever two of the diodes are being in parallel to the secondary of the transformer, the maximum secondary voltage across the transformer appears at the non-conducting diodes which makes the PIV of the rectifier circuit. Hence the peak inverse voltage is the maximum voltage across the

Electronic Circuits – Positive Clipper Circuits The Clipper circuit that is intended to attenuate positive portions of the input signal can be termed as a Positive Clipper. Among the positive diode clipper circuits, we have the following types − Positive Series Clipper Positive Series Clipper with positive $V_{r}$ (reference voltage) Positive Series Clipper with negative $V_{r}$ Positive Shunt Clipper Positive Shunt Clipper with positive $V_{r}$ Positive Shunt Clipper with negative $V_{r}$ Let us discuss each of these types in detail. Positive Series Clipper A Clipper circuit in which the diode is connected in series to the input signal and that attenuates the positive portions of the waveform, is termed as Positive Series Clipper. The following figure represents the circuit diagram for positive series clipper. Positive Cycle of the Input − When the input voltage is applied, the positive cycle of the input makes the point A in the circuit positive with respect to the point B. This makes the diode reverse biased and hence it behaves like an open switch. Thus the voltage across the load resistor becomes zero as no current flows through it and hence $V_{0}$ will be zero. Negative Cycle of the Input − The negative cycle of the input makes the point A in the circuit negative with respect to the point B. This makes the diode forward biased and hence it conducts like a closed switch. Thus the voltage across the load resistor will be equal to the applied input voltage as it completely appears at the output $V_{0}$. Waveforms In the above figures, if the waveforms are observed, we can understand that only a portion of the positive peak was clipped. This is because of the voltage across V0. But the ideal output was not meant to be so. Let us have a look at the following figures. Unlike the ideal output, a bit portion of the positive cycle is present in the practical output due to the diode conduction voltage which is 0.7v. Hence there will be a difference in the practical and ideal output waveforms. Positive Series Clipper with positive $V_{r}$ A Clipper circuit in which the diode is connected in series to the input signal and biased with positive reference voltage $V_{r}$ and that attenuates the positive portions of the waveform, is termed as Positive Series Clipper with positive $V_{r}$. The following figure represents the circuit diagram for positive series clipper when the reference voltage applied is positive. During the positive cycle of the input the diode gets reverse biased and the reference voltage appears at the output. During its negative cycle, the diode gets forward biased and conducts like a closed switch. Hence the output waveform appears as shown in the above figure. Positive Series Clipper with negative $V_{r}$ A Clipper circuit in which the diode is connected in series to the input signal and biased with negative reference voltage $V_{r}$ and that attenuates the positive portions of the waveform, is termed as Positive Series Clipper with negative $V_{r}$. The following figure represents the circuit diagram for positive series clipper, when the reference voltage applied is negative. During the positive cycle of the input the diode gets reverse biased and the reference voltage appears at the output. As the reference voltage is negative, the same voltage with constant amplitude is shown. During its negative cycle, the diode gets forward biased and conducts like a closed switch. Hence the input signal that is greater than the reference voltage, appears at the output. Positive Shunt Clipper A Clipper circuit in which the diode is connected in shunt to the input signal and that attenuates the positive portions of the waveform, is termed as Positive Shunt Clipper. The following figure represents the circuit diagram for positive shunt clipper. Positive Cycle of the Input − When the input voltage is applied, the positive cycle of the input makes the point A in the circuit positive with respect to the point B. This makes the diode forward biased and hence it conducts like a closed switch. Thus the voltage across the load resistor becomes zero as no current flows through it and hence $V_{0}$ will be zero. Negative Cycle of the Input − The negative cycle of the input makes the point A in the circuit negative with respect to the point B. This makes the diode reverse biased and hence it behaves like an open switch. Thus the voltage across the load resistor will be equal to the applied input voltage as it completely appears at the output $V_{0}$. Waveforms In the above figures, if the waveforms are observed, we can understand that only a portion of the positive peak was clipped. This is because of the voltage across $V_{0}$. But the ideal output was not meant to be so. Let us have a look at the following figures. Unlike the ideal output, a bit portion of the positive cycle is present in the practical output due to the diode conduction voltage which is 0.7v. Hence there will be a difference in the practical and ideal output waveforms. Positive Shunt Clipper with positive $V_{r}$ A Clipper circuit in which the diode is connected in shunt to the input signal and biased with positive reference voltage $V_{r}$ and that attenuates the positive portions of the waveform, is termed as Positive Shunt Clipper with positive $V_{r}$. The following figure represents the circuit diagram for positive shunt clipper when the reference voltage applied is positive. During the positive cycle of the input the diode gets forward biased and nothing but the reference voltage appears at the output. During its negative cycle, the diode gets reverse biased and behaves as an open switch. The whole of the input appears at the output. Hence the output waveform appears as shown in the above figure. Positive Shunt Clipper with negative $V_{r}$ A Clipper circuit in which the diode is connected in shunt to the input signal and biased with negative reference voltage $V_{r}$ and that attenuates the positive portions

Electronic Circuits – Diode as a Switch Diode is a two terminal PN junction that can be used in various applications. One of such applications is an electrical switch. The PN junction, when forward biased acts as close circuited and when reverse biased acts as open circuited. Hence the change of forward and reverse biased states makes the diode work as a switch, the forward being ON and the reverse being OFF state. Electrical Switches over Mechanical Switches Electrical switches are a preferred choice over mechanical switches due to the following reasons − Mechanical switches are prone to oxidation of metals whereas electrical switches don’t. Mechanical switches have movable contacts. They are more prone to stress and strain than electrical switches. The worn and torn of mechanical switches often affect their working. Hence an electrical switch is more useful than a Mechanical switch. Working of Diode as a Switch Whenever a specified voltage is exceeded, the diode resistance gets increased, making the diode reverse biased and it acts as an open switch. Whenever the voltage applied is below the reference voltage, the diode resistance gets decreased, making the diode forward biased, and it acts as a closed switch. The following circuit explains the diode acting as a switch. A switching diode has a PN junction in which P-region is lightly doped and N-region is heavily doped. The above circuit symbolizes that the diode gets ON when positive voltage forward biases the diode and it gets OFF when negative voltage reverse biases the diode. Ringing As the forward current flows till then, with a sudden reverse voltage, the reverse current flows for an instance rather than getting switched OFF immediately. The higher the leakage current, the greater the loss. The flow of reverse current when diode is reverse biased suddenly, may sometimes create few oscillations, called as RINGING. This ringing condition is a loss and hence should be minimized. To do this, the switching times of the diode should be understood. Diode Switching Times While changing the bias conditions, the diode undergoes a transient response. The response of a system to any sudden change from an equilibrium position is called as transient response. The sudden change from forward to reverse and from reverse to forward bias, affects the circuit. The time taken to respond to such sudden changes is the important criterion to define the effectiveness of an electrical switch. The time taken before the diode recovers its steady state is called as Recovery Time. The time interval taken by the diode to switch from reverse biased state to forward biased state is called as Forward Recovery Time.($t_{fr}$) The time interval taken by the diode to switch from forward biased state to reverse biased state is called as Reverse Recovery Time. ($t_{fr}$) To understand this more clearly, let us try to analyze what happens once the voltage is applied to a switching PN diode. Carrier Concentration Minority charge carrier concentration reduces exponentially as seen away from the junction. When the voltage is applied, due to the forward biased condition, the majority carriers of one side move towards the other. They become minority carriers of the other side. This concentration will be more at the junction. For example, if N-type is considered, the excess of holes that enter into N-type after applying forward bias, adds to the already present minority carriers of N-type material. Let us consider few notations. The majority carriers in P-type (holes) = $P_{po}$ The majority carriers in N-type (electrons) = $N_{no}$ The minority carriers in P-type (electrons) = $N_{po}$ The majority carriers in N-type (holes) = $P_{no}$ During Forward biased Condition − The minority carriers are more near junction and less far away from the junction. The graph below explains this. Excess minority carrier charge in P-type = $P_n-P_{no}$ with $p_{no}$ (steady state value) Excess minority carrier charge in N-type = $N_p-N_{po}$ with $N_{po}$ (steady state value) During reverse bias condition − Majority carriers doesn’t conduct the current through the junction and hence don’t participate in current condition. The switching diode behaves as a short circuited for an instance in reverse direction. The minority carriers will cross the junction and conduct the current, which is called as Reverse Saturation Current. The following graph represents the condition during reverse bias. In the above figure, the dotted line represents equilibrium values and solid lines represent actual values. As the current due to minority charge carriers is large enough to conduct, the circuit will be ON until this excess charge is removed. The time required for the diode to change from forward bias to reverse bias is called Reverse recovery time ($t_{rr}$). The following graphs explain the diode switching times in detail. From the above figure, let us consider the diode current graph. At $t_{1}$ the diode is suddenly brought to OFF state from ON state; it is known as Storage time. Storage time is the time required to remove the excess minority carrier charge. The negative current flowing from N to P type material is of a considerable amount during the Storage time. This negative current is, $$-I_R= frac{-V_{R}}{R}$$ The next time period is the transition time” (from $t_2$ to $t_3$) Transition time is the time taken for the diode to get completely to open circuit condition. After $t_3$ diode will be in steady state reverse bias condition. Before $t_1$ diode is under steady state forward bias condition. So, the time taken to get completely to open circuit condition is $$Reverse ::recovery:: timeleft ( t_{rr} right )= Storage ::time left ( T_{s} right )+Transition :: time left ( T_{t} right )$$ Whereas to get to ON condition from OFF, it takes less time called as Forward recovery time. Reverse recovery time is greater than Forward recovery time. A diode works as a better switch if this Reverse recovery time is made less. Definitions Let us just go through the definitions of the time periods discussed. Storage time − The time period for which the diode remains in the conduction

Nonlinear Wave Shapping Along with resistors, the non-linear elements like diodes are used in nonlinear wave shaping circuits to get required altered outputs. Either the shape of the wave is attenuated or the dc level of the wave is altered in the Non-linear wave shaping. The process of producing non-sinusoidal output wave forms from sinusoidal input, using non-linear elements is called as nonlinear wave shaping. Clipper Circuits A Clipper circuit is a circuit that rejects the part of the input wave specified while allowing the remaining portion. The portion of the wave above or below the cut off voltage determined is clipped off or cut off. The clipping circuits consist of linear and non-linear elements like resistors and diodes but not energy storage elements like capacitors. These clipping circuits have many applications as they are advantageous. The main advantage of clipping circuits is to eliminate the unwanted noise present in the amplitudes. These can work as square wave converters, as they can convert sine waves into square waves by clipping. The amplitude of the desired wave can be maintained at a constant level. Among the Diode Clippers, the two main types are positive and negative clippers. We will discuss these two types of clippers in the next two chapters. Learning working make money

Special Functions of LPF and HPF Low-pass and high-pass filter circuits are used as special circuits in many applications. Low-pass filter (LPF) can work as an Integrator, whereas the high-pass filter (HPF) can work as a Differentiator. These two mathematical functions are possible only with these circuits which reduce the efforts of an electronics engineer in many applications. Low Pass Filter as Integrator At low frequencies, the capacitive reactance tends to become infinite and at high frequencies the reactance becomes zero. Hence at low frequencies, the LPF has finite output and at high frequencies the output is nil, which is same for an integrator circuit. Hence low pass filter can be said to be worked as an integrator. For the LPF to behave as an integrator $$tau gg T$$ Where $tau = RC$ the time constant of the circuit Then the voltage variation in C is very small. $$V_{i}=iR+frac{1}{C} int i :dt$$ $$V_{i}cong iR$$ $$Since :: frac{1}{C} int i :dt ll iR$$ $$i=frac{V_{i}}{R}$$ $$ Since :: V_{0}=frac{1}{C}int i dt =frac{1}{RC}int V_{i}dt=frac{1}{tau }int V_{i} dt$$ $$Output propto int input$$ Hence a LPF with large time constant produces an output that is proportional to the integral of an input. Frequency Response The Frequency response of a practical low pass filter, when it works as an Integrator is as shown below. Output Waveform If the integrator circuit is given a sinewave input, the output will be a cosine wave. If the input is a square wave, the output wave form changes its shape and appears as in the figure below. High Pass Filter as Differentiator At low frequencies, the output of a differentiator is zero whereas at high frequencies, its output is of some finite value. This is same as for a differentiator. Hence the high pass filter is said to be behaved as a differentiator. If time constant of the RC HPF is very much smaller than time period of the input signal, then circuit behaves as a differentiator. Then the voltage drop across R is very small when compared to the drop across C. $$V_{i}=frac{1}{C}int i :dt +iR$$ But $iR=V_{0}$ is small $$since V_{i}=frac{1}{C}int i :dt$$ $$i=frac{V_{0}}{R}$$ $$Since : V_{i} =frac{1}{tau }int V_{0} :dt$$ Where $tau =RC$ the time constant of the circuit. Differentiating on both sides, $$frac{dV_{i}}{dt}=frac{V_0}{tau }$$ $$V_{0}=tau frac{dV_{i}}{dt}$$ $$Since :V_{0}propto frac{dV_{i}}{dt}$$ The output is proportional to the differential of the input signal. Frequency Response The Frequency response of a practical high pass filter, when it works as a Differentiator is as shown below. Output Wave form If the differentiator circuit is given a sinewave input, the output will be a cosine wave. If the input is a square wave, the output wave form changes its shape and appears as in the figure below. These two circuits are mostly used in various electronic applications. A differentiator circuit produces a constant output voltage when the input applied tends to change steadily. An integrator circuit produces a steadily changing output voltage when the input voltage applied is constant. Learning working make money

Electronic Circuits – Negative Clipper Circuits The Clipper circuit that is intended to attenuate negative portions of the input signal can be termed as a Negative Clipper. Among the negative diode clipper circuits, we have the following types. Negative Series Clipper Negative Series Clipper with positive $V_{r}$ (reference voltage) Negative Series Clipper with negative $V_{r}$ Negative Shunt Clipper Negative Shunt Clipper with positive $V_{r}$ Negative Shunt Clipper with negative $V_{r}$ Let us discuss each of these types in detail. Negative Series Clipper A Clipper circuit in which the diode is connected in series to the input signal and that attenuates the negative portions of the waveform, is termed as Negative Series Clipper. The following figure represents the circuit diagram for negative series clipper. Positive Cycle of the Input − When the input voltage is applied, the positive cycle of the input makes the point A in the circuit positive with respect to the point B. This makes the diode forward biased and hence it acts like a closed switch. Thus the input voltage completely appears across the load resistor to produce the output $V_{0}$. Negative Cycle of the Input − The negative cycle of the input makes the point A in the circuit negative with respect to the point B. This makes the diode reverse biased and hence it acts like an open switch. Thus the voltage across the load resistor will be zero making $V_{0}$ zero. Waveforms In the above figures, if the waveforms are observed, we can understand that only a portion of the negative peak was clipped. This is because of the voltage across $V_{0}$. But the ideal output was not meant to be so. Let us have a look at the following figures. Unlike the ideal output, a bit portion of the negative cycle is present in the practical output due to the diode conduction voltage which is 0.7v. Hence there will be a difference in the practical and ideal output waveforms. Negative Series Clipper with positive $V_{r}$ A Clipper circuit in which the diode is connected in series to the input signal and biased with positive reference voltage $V_{r}$ and that attenuates the negative portions of the waveform, is termed as Negative Series Clipper with positive $V_{r}$. The following figure represents the circuit diagram for negative series clipper when the reference voltage applied is positive. During the positive cycle of the input, the diode starts conducting only when the anode voltage value exceeds the cathode voltage value of the diode. As the cathode voltage equals the reference voltage applied, the output will be as shown. Negative Series Clipper with negative $V_{r}$ A Clipper circuit in which the diode is connected in series to the input signal and biased with negative reference voltage $V_{r}$ and that attenuates the negative portions of the waveform, is termed as Negative Series Clipper with negative $V_{r}$. The following figure represents the circuit diagram for negative series clipper, when the reference voltage applied is negative. During the positive cycle of the input the diode gets forward biased and the input signal appears at the output. During its negative cycle, the diode gets reverse biased and hence will not conduct. But the negative reference voltage being applied, appears at the output. Hence the negative cycle of the output waveform gets clipped after this reference level. Negative Shunt Clipper A Clipper circuit in which the diode is connected in shunt to the input signal and that attenuates the negative portions of the waveform, is termed as Negative Shunt Clipper. The following figure represents the circuit diagram for negative shunt clipper. Positive Cycle of the Input − When the input voltage is applied, the positive cycle of the input makes the point A in the circuit positive with respect to the point B. This makes the diode reverse biased and hence it behaves like an open switch. Thus the voltage across the load resistor equals the applied input voltage as it completely appears at the output $V_{0}$ Negative Cycle of the Input − The negative cycle of the input makes the point A in the circuit negative with respect to the point B. This makes the diode forward biased and hence it conducts like a closed switch. Thus the voltage across the load resistor becomes zero as no current flows through it. Waveforms In the above figures, if the waveforms are observed, we can understand that just a portion of the negative peak was clipped. This is because of the voltage across $V_{0}$. But the ideal output was not meant to be so. Let us have a look at the following figures. Unlike the ideal output, a bit portion of the negative cycle is present in the practical output due to the diode conduction voltage which is 0.7v. Hence there will be a difference in the practical and ideal output waveforms. Negative Shunt Clipper with positive $V_{r}$ A Clipper circuit in which the diode is connected in shunt to the input signal and biased with positive reference voltage $V_{r}$ and that attenuates the negative portions of the waveform, is termed as Negative Shunt Clipper with positive $V_{r}$. The following figure represents the circuit diagram for negative shunt clipper when the reference voltage applied is positive. During the positive cycle of the input the diode gets reverse biased and behaves as an open switch. So whole of the input voltage, which is greater than the reference voltage applied, appears at the output. The signal below reference voltage level gets clipped off. During the negative half cycle, as the diode gets forward biased and the loop gets completed, no output is present. Negative Shunt Clipper with negative $V_{r}$ A Clipper circuit in which the diode is connected in shunt to the input signal and biased with negative reference voltage $V_{r}$ and that attenuates the negative portions of the waveform, is termed as Negative Shunt Clipper with negative $V_{r}$. The following figure represents the circuit diagram for negative shunt clipper, when the reference voltage applied is

Electronic Circuits – Introduction In Electronics, we have different components that serve different purposes. There are various elements which are used in many types of circuits depending on the applications. Electronic Components Similar to a brick that constructs a wall, a component is the basic brick of a circuit. A Component is a basic element that contributes for the development of an idea into a circuit for execution. Each component has a few basic properties and the component behaves accordingly. It depends on the motto of the developer to use them for the construction of the intended circuit. The following image shows a few examples of electronic components that are used in different electronic circuits. Just to gather an idea, let us look at the types of Components. They can either be Active Components or Passive Components. Active Components Active Components are those which conduct upon providing some external energy. Active Components produce energy in the form of voltage or current. Examples − Diodes, Transistors, Transformers, etc. Passive Components Passive components are those which start their operation once they are connected. No external energy is needed for their operation. Passive components store and maintain energy in the form of voltage or current. Examples − Resistors, Capacitors, Inductors, etc. We also have another classification as Linear and Non-Linear elements. Linear Components Linear elements or components are the ones that have linear relationship between current and voltage. The parameters of linear elements are not changed with respect to current and voltage. Examples − Diodes, Transistors, Transformers, etc. Non-linear Components Non-linear elements or components are the ones that have a non-linear relationship between current and voltage. The parameters of non-linear elements are changed with respect to current and voltage. Examples − Resistors, Capacitors, Inductors, etc. These are the components intended for various purposes, which altogether can perform a preferred task for which they are built. Such a combination of different components is known as a Circuit. Electronic Circuits A certain number of components when connected on a purpose in a specific fashion makes a circuit. A circuit is a network of different components. There are different types of circuits. The following image shows different types of electronic circuits. It shows Printed Circuit Boards which are a group of electronic circuits connected on a board. Electronic circuits can be grouped under different categories depending upon their operation, connection, structure, etc. Let’s discuss more about the types of Electronic Circuits. Active Circuit A circuit that is build using Active components is called as Active Circuit. It usually contains a power source from which the circuit extracts more power and delivers it to the load. Additional Power is added to the output and hence output power is always greater than the input power applied. The power gain will always be greater than unity. Passive Circuit A circuit that is build using Passive components is called as Passive Circuit. Even if it contains a power source, the circuit does not extract any power. Additional Power is not added to the output and hence output power is always less than the input power applied. The power gain will always be less than unity. Electronic circuits can also be classified as Analog, Digital, or Mixed. Analog Circuit An analog circuit can be one which has linear components in it. Hence it is a linear circuit. An analog circuit has analog signal inputs which are continuous range of voltages. Digital Circuit A digital circuit can be one which has non-linear components in it. Hence it is a non-linear circuit. It can process digital signals only. A digital circuit has digital signal inputs which are discrete values. Mixed Signal Circuit A mixed signal circuit can be one which has both linear and non-linear components in it. Hence it is called as a mixed signal circuit. These circuits consist of analog circuitry along with microprocessors to process the input. Depending upon the type of connection, circuits can be classified as either Series Circuit or Parallel Circuit. A Series Circuit is one which is connected in series and a parallel circuit is one which has its components connected in parallel. Now that we have a basic idea about electronic components, let us move on and discuss their purpose which will help us build better circuits for different applications. Whatever might be the purpose of an electronic circuit (to process, to send, to receive, to analyze), the process is carried out in the form of signals. In the next chapter, we will discuss the signals and the type of signals present in electronic circuits. Learning working make money