Electrical4U 
Both N-channel and P-channel JFETs can switch analogue signals. A JFET is a normally-on depletion device: zero gate-source voltage opens the channel, while a reverse gate-source voltage moves it toward cutoff. An ideal closed switch has zero resistance, and an ideal open switch has zero leakage. A real JFET has finite on-resistance, off-state leakage, capacitance … Read more
Junction field-effect transistors have two channel polarities:N-channel JFETP-channel JFETThe output characteristic plots drain current against drain-source voltage for several gate-source voltages. The transfer characteristic plots drain current against gate-source voltage at a stated drain-source voltage. Both plots need their voltage polarities and test conditions. Characteristic of N Channel JFET An N-channel JFET has an N-type … Read more
JFET biasing establishes the no-signal drain current, drain-source voltage and gate-source voltage. Pinch-off and cutoff are different limits, so the voltage symbol and test condition must be stated before using either value in a bias calculation. Pinch Off Voltage For an n-channel JFET with source and gate grounded, a positive drain voltage causes conventional drain … Read more
A bipolar junction transistor uses both majority and minority carriers. Its collector current has an exponential relationship to base-emitter voltage, while base current provides the terminal drive in common circuit models. A junction field-effect transistor is a majority-carrier device whose reverse-biased gate junction controls channel width. Because normal gate current is only leakage, a JFET … Read more
A common-source JFET amplifier needs a DC bias before an AC gate signal is applied. The no-signal drain current and drain-source voltage define the quiescent operating point. A useful bias keeps the intended signal excursion within the desired constant-current region and away from cutoff, excessive channel resistance and device ratings. The circuit’s load line analysis … Read more
This explanation covers a silicon NPN transistor in common-emitter forward-active operation. The emitter is heavily doped to inject electrons, the base is thin and lightly doped, and the collector is more lightly doped than the emitter. The collector is often made physically larger to withstand voltage and dissipate heat. These are functional design trends, not … Read more
Electric machines, also called electrical machines, use electromagnetic fields to transfer or convert electrical energy. A transformer transfers power between electrical circuits. A generator converts mechanical power to electricity, while a motor converts electrical power to mechanical power. Types of Electrical Machines Three broad groups covered here are the transformer, generator and motor.Transformers: A transformer … Read more
The wheel, electricity, telecommunications and the computer have each changed daily life. This introduction to electricity uses electricity as the broad term for phenomena involving electric charge, electric fields, voltage, current and electrical energy. Electric current is one part of that subject, not a complete definition of electricity. Ordinary matter contains positive protons and negative … Read more
Magnetism describes interactions involving magnetic fields, moving electric charge, magnetic moments and magnetic materials. Motors, generators, transformers, sensors and many other electrical devices use these interactions. A permanent magnet produces a field without continuous external power. It strongly attracts ferromagnetic materials such as iron, cobalt, nickel and many of their alloys. A freely suspended small … Read more
What is Electrical Impedance? Electrical impedance Z is the complex ratio of voltage to current at a stated frequency. In sinusoidal steady-state analysis, the voltage and current are represented by phasors, so Z = V/I in ohms. This extends Ohm’s law to linear alternating current circuits and records both the magnitude ratio and phase difference. … Read more