Analog Electronics In A Day Analog Electronic Design Inductors The equation for the impedance of an inductor is X,=sL where s=ja Inductors have poor tolerance, and they are Power supplies and filters use inductors Inductors requiring cores are big and heavy Only the high frequency or signal fil inductor is modeled 1-22 types primary use for inductors is for filters. There are two very different of filter inductors: the high current inductor used in power supply filters, and the low current inductors used in signal filters High current inductors require cores to keep the losses within acceptable limits and to achieve high performance. The cores are big and heavy, so they contribute heavily to the cost, weight, and size of the equipment Switching power supplies require extensive inductors or transformers to control the switching noise and smooth out the output voltage waveform Low current inductors are used for filters in signal processing circuits Capacitors are used where ever possible because they are less expensive and readily available, but there are a few applications that inductors excel in. An inductive/capacitive filter has sharper slopes than a resistive/capacitive filter, thus it is a more effective filter in some applications. In general, inductors are rarely seen outside power circuits
1-22 Analog Electronics In A Day Analog Electronic Design 1-22 • The equation for the impedance of an inductor is XL=sL where s=jω. • Inductors have poor tolerance, and they are expensive. • Power supplies and filters use inductors. • Inductors requiring cores are big and heavy. • Only the high frequency or signal filter inductor is modeled. The primary use for inductors is for filters. There are two very different types of filter inductors: the high current inductor used in power supply filters, and the low current inductors used in signal filters. High current inductors require cores to keep the losses within acceptable limits and to achieve high performance. The cores are big and heavy, so they contribute heavily to the cost, weight, and size of the equipment. Switching power supplies require extensive inductors or transformers to control the switching noise and smooth out the output voltage waveform. Low current inductors are used for filters in signal processing circuits. Capacitors are used where ever possible because they are less expensive and readily available, but there are a few applications that inductors excel in. An inductive/capacitive filter has sharper slopes than a resistive/capacitive filter, thus it is a more effective filter in some applications. In general, inductors are rarely seen outside power circuits
Analog Electronics In A Day Analog Electronic Design Inductor model The inductor model is rather simple consisting of the inductor, L, a series resistance, Rs, and the parallel capacitance, Cp. The series resistance impacts the performance of the inductor considerably, and great efforts are made to keep Rs at a minimum, especially in power inductors. Cp does not come into play until the signal frequencies get in the MHz range The parallel capacitance degrades the inductor performance at high frequencies
1-23 Analog Electronics In A Day Analog Electronic Design 1-23 L CP RS The inductor model is rather simple consisting of the inductor, L, a series resistance, RS, and the parallel capacitance, CP. The series resistance impacts the performance of the inductor considerably, and great efforts are made to keep RS at a minimum, especially in power inductors. CP does not come into play until the signal frequencies get in the MHz range. The parallel capacitance degrades the inductor performance at high frequencies
Analog Electronics In A Day Analog Electronic Design Diodes Anode、; Cathode Diodes conduct current in one direction and they block current in the reverse direction Forward biased diodes have a forward voltage drop of 0.6v, and a resistance of r=26/l Diodes can block very large voltages in the reverse direction Diodes are used to block unwanted signals Diodes must be biased to be used and often the circuit using the diode provides the bias. Forward biased diodes have the most positive voltage applied to their anode, while reversed biased diodes have the most positive voltage applied to their cathode. Forward biased diodes pass current in the forward direction which is the direction of the arrow and reverse biased diodes block current flow forwards biased diodes exhibit a low resistance, and reverse biased diodes exhibit a high resistance a diode is used to make a positive peak detector by letting the signal forward bias the diode and storing the resultant voltage on a capacitor Lesser voltages do not forward bias the diode, so they are ignored. When a diode is forward biased it is low resistance so it can pass a signal, and when it is reverse biased, the diode is high resistance thus blocking the signal. Connecting the cathode of a diode to ground means that the voltage across the diode will not exceed the forward biased diode drop of approximately 0.6 volts
1-24 Analog Electronics In A Day Analog Electronic Design 1-24 Anode Cathode • Diodes conduct current in one direction, and they block current in the reverse direction. • Forward biased diodes have a forward voltage drop of 0.6V, and a resistance of re=26/I • Diodes can block very large voltages in the reverse direction. • Diodes are used to block unwanted signals. Diodes must be biased to be used, and often the circuit using the diode provides the bias. Forward biased diodes have the most positive voltage applied to their anode, while reversed biased diodes have the most positive voltage applied to their cathode. Forward biased diodes pass current in the forward direction which is the direction of the arrow, and reverse biased diodes block current flow. Forwards biased diodes exhibit a low resistance, and reverse biased diodes exhibit a high resistance. A diode is used to make a positive peak detector by letting the signal forward bias the diode and storing the resultant voltage on a capacitor. Lesser voltages do not forward bias the diode, so they are ignored. When a diode is forward biased it is low resistance so it can pass a signal, and when it is reverse biased, the diode is high resistance thus blocking the signal. Connecting the cathode of a diode to ground means that the voltage across the diode will not exceed the forward biased diode drop of approximately 0.6 volts
Analog Electronics In A Day Analog Electronic Design Diode model 0,W The forward voltage drop, VE, is shown as a battery. The forward biased diode starts with a small voltage drop, but it very quickly rises to approximately 0.6 volts for a silicon diode and 0.2 volts for a germanium diode The voltage drop is a function of the bias current, but these approximations suffice for the majority of applications The diode resistance, re, is also a function of the forward current, and it is approximated by the equation re 26/1. This is an approximation of re, but it holds over a wide range of currents. When the diode is reverse biased the forward current is zero, and the equation says that re equals infinity This is not exactly true, but the relationship is too complicated for this discussion. a simple way out of the trap is to include the current source, IL, which models a reverse biased leakage current. The leakage current is voltage and temperature sensitive, so it is best to use diodes which have very low leakage currents Diodes take a finite amount of time to turn on and turn off. some of this time results from the carrier physics internal to the diode, and some of this time results from the parallel capacitance, Cp. Depending on the diode and the bias conditions, Cp ranges from a fraction of a pF for smal itching diodes to a few hundred pF for power diodes. Remember, diodes have switching times that may have to be accounted for
1-25 Analog Electronics In A Day Analog Electronic Design 1-25 VF re CP IL The forward voltage drop, VF, is shown as a battery. The forward biased diode starts with a small voltage drop, but it very quickly rises to approximately 0.6 volts for a silicon diode and 0.2 volts for a germanium diode The voltage drop is a function of the bias current, but these approximations suffice for the majority of applications. The diode resistance, re, is also a function of the forward current, and it is approximated by the equation re = 26/I. This is an approximation of re, but it holds over a wide range of currents. When the diode is reverse biased the forward current is zero, and the equation says that re equals infinity. This is not exactly true, but the relationship is too complicated for this discussion. A simple way out of the trap is to include the current source, IL, which models a reverse biased leakage current. The leakage current is voltage and temperature sensitive, so it is best to use diodes which have very low leakage currents. Diodes take a finite amount of time to turn on and turn off. Some of this time results from the carrier physics internal to the diode, and some of this time results from the parallel capacitance, CP. Depending on the diode and the bias conditions, CP ranges from a fraction of a pF for small switching diodes to a few hundred pF for power diodes. Remember, diodes have switching times that may have to be accounted for
Analog Electronics In A Day Analog Electronic Design Active Devices Active devices have gain; thus they can make up transfer functions not available to passive devices. Active devices are considerably more complicated than passive devices; thus, their models and transfer equations are more complicated than those of passive devices. Active devices are the foundation of all electronics
1-26 Analog Electronics In A Day Analog Electronic Design 1-26 Active devices have gain; thus they can make up transfer functions not available to passive devices. Active devices are considerably more complicated than passive devices; thus, their models and transfer equations are more complicated than those of passive devices. Active devices are the foundation of all electronics