The invention of the bipolar transistor in 1948 ushered in a revolution in electronics. Technical feats previously requiring relatively large, mechanically fragile, power-hungry vacuum tubes were suddenly achievable with tiny, mechanically rugged, power-thrifty specks of crystalline silicon. This revolution made possible the design and manufacture of lightweight, inexpensive electronic devices that we now take for [...]
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Transistor Active mode operation
When a transistor is in the fully-off state (like an open switch), it is said to be cutoff. Conversely, when it is fully conductive between emitter and collector (passing as much current through the collector as the collector power supply and load will allow), it is said to be saturated. These are the two modes [...]
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Transistors : Feedback
If some percentage of an amplifier’s output signal is connected to the input, so that the amplifier amplifies part of its own output signal, we have what is known as feedback. Feedback comes in two varieties: positive (also called regenerative), and negative (also called degenerative). Positive feedback reinforces the direction of an amplifier’s output voltage [...]
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Amplifier impedances
Input impedance varies considerably with the circuit configuration shown in Figure below. It also varies with biasing. Not considered here, the input impedance is complex and varies with frequency. For the common-emitter and common-collector it is base resistance times ?. The base resistance can be both internal and external to the transistor. For the common-collector: [...]
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Transistor as a switch
Because a transistor’s collector current is proportionally limited by its base current, it can be used as a sort of current-controlled switch. A relatively small flow of electrons sent through the base of the transistor has the ability to exert control over a much larger flow of electrons through the collector. Suppose we had a [...]
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Transistor ratings and packages
Like all electrical and electronic components, transistors are limited in the amounts of voltage and current each one can handle without sustaining damage. Since transistors are more complex than some of the other components you’re used to seeing at this point, these tend to have more kinds of ratings. What follows is an itemized description [...]
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ELECTRONIC THERMOSTAT SOLUTION CIRCUIT
The circuit for the low-cost thermostat solution is shown in Figure 5. Power to the microcontroller is provided by a transformerless resistive power supply. An analysis of resistive power supplies is given in application note AN954, Transformerless Power Supplies: Resistive and Capacitive. The resistive power supply was sized to provide the necessary current for powering [...]
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Electric Control Using a Triac
Most countertop cooking appliances like electric ranges, skillets and fryers have an adjustable mechanical thermostat to vary the heat output of the range. This solution is inexpensive, but there are several drawbacks to mechanical thermostats: • Mechanical thermostats have to be calibrated at the factory. • They have poor simmer performance (control is not precise [...]
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Current mirrors Transistors
An often-used circuit applying the bipolar junction transistor is the so-called current mirror, which serves as a simple current regulator, supplying nearly constant current to a load over a wide range of load resistances. We know that in a transistor operating in its active mode, collector current is equal to base current multiplied by the [...]
AMPLIFIERS10
Transistor:Input and output coupling
To overcome the challenge of creating necessary DC bias voltage for an amplifier’s input signal without resorting to the insertion of a battery in series with the AC signal source, we used a voltage divider connected across the DC power source. To make this work in conjunction with an AC input signal, we “coupled” the [...]
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transistors : Biasing calculations
Although transistor switching circuits operate without bias, it is unusual for analog circuits to operate without bias. One of the few examples is “TR One, one transistor radio” TR One, Ch 9 with an amplified AM (amplitude modulation) detector. Note the lack of a bias resistor at the base in that circuit. In this section [...]
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Transistor : Biasing techniques
Biasing techniques In the common-emitter section of this chapter, we saw a SPICE analysis where the output waveform resembled a half-wave rectified shape: only half of the input waveform was reproduced, with the other half being completely cut off. Since our purpose at that time was to reproduce the entire waveshape, this constituted a problem. [...]
