Electrical4U What is a Relaxation Oscillator? A relaxation oscillator is a nonlinear electronic oscillator that produces a repeating non-sine wave, such as a square, triangle or pulse. Henri Abraham and Eugène Bloch built a vacuum-tube multivibrator around 1918. The name relaxation oscillation came later from van der Pol. A later electronic oscillator of this class still … Read more
What is an Electrical Resistor? A resistor is a two-terminal passive electrical element that inserts a set electrical resistance into a circuit. Resistance is the opposition to current. A larger ohm value lets less current flow for the same voltage. Catalogue types of resistors include the thermistor and many fixed parts. Its job in a … Read more
Electrical4U is a progressive web app. You add it to an iPhone or iPad home screen from Safari. You do not install it from the App Store. app.electrical4u.com is the Electrical4U app address on every platform. The steps below are for iPhone and iPad. Use Safari (not Chrome or Firefox) and follow these steps: Open … Read more
What is RMS Voltage? RMS means root-mean-square. RMS voltage is the square root of the mean of the squares of the instantaneous values. That quadratic mean can also be written as an integral of v² over one period, then divided by the period, then square-rooted. AC voltage changes from instant to instant. A single snapshot … Read more
What is DC Voltage? DC voltage means a voltage that does not reverse polarity. It produces, or would produce, a DC current. AC voltage reverses polarity and produces alternating current. DC here also covers quantities that do not regularly reverse polarity, or whose frequency is zero or near zero. AC covers quantities that reverse polarity … Read more
What is Electric Current? Electric current is the net flow of charged particles (electrons, ions or holes) through a conductor or through space. Instantaneous current is how fast electric charge passes a surface: I = dQ/dt. Circuit symbols are I or i. The SI unit is the ampere (A). In symbols, The moving particles in … Read more
What is a Ballast Resistor? A ballast resistor is a series resistor that limits current so a load cannot draw an unbounded current. The broader term electric ballast covers any current-limiting device, including resistors, capacitors and inductors. A fixed ballast resistor has a nearly constant resistance. A self-variable ballast, such as a barretter, raises resistance … Read more
What is Norton Theorem? (Norton’s Equivalent Circuit) Norton’s theorem (Mayer and Norton, 1926) says a linear two-terminal network can be replaced, at those terminals, by one current source IN in parallel with one resistance RN (or impedance ZN). That pair, plus the load, is the Norton equivalent circuit. Linear dependent sources inside the network are … Read more
What is Settling Time? Settling time Ts is the first time after which the step response stays inside a stated error band around the final value, and remains there. That interval includes delay, rise, any overshoot and the ring-down until the band is never left again. Overload recovery of an amplifier is a related but … Read more
What is Voltage? Voltage is the electric potential difference between two points: the work per unit charge to move a test charge between those points in an electric field. In circuit work the usual symbols are V and, in older texts, E. Calling voltage “potential difference per unit charge” would divide volts by coulombs. EMF … Read more