Formulas and Reference Data

Topics Covered:

• Basic Formulas
• Glossary of Power Supply Terms
• Conversion Factors
• Power Conversion Table - dBm to Watts (PDF file)   New
• Greek Alphabet/Symbol Key

Basic Formulas:

Term	Formula
Reactance
Conductance	G = 1     and      g = 1         R                      r
Susceptance	B = 1     and      b = 1        X                      x
Impedance (Z0 is the Characteristic Impedance)
Admittance (Y0 is the Characteristic Admittance)
Reflection Coefficient
Voltage Standing Wave Ratio
Return Loss
Mismatch Loss (GS¹0, GL¹0)
Wavelength
Conversion to dB

Printable version of the Basic Formulas table

Formula Calculator:

Glossary of Power Supply Terms:

Analog—The traditional method of telecommunications. A transmission method employing a continuous (rather than pulse or digital) electrical signal that varies in amplitude or frequency in response to changes in sound impressed on a transducer in the sending device.

Attenuation—The decrease in amplitude of a signal during its transmission from one point to another. Usually expressed as a ratio or in decibels.

Bandwidth—The relative range of frequencies that can be passed through a transmission medium without distortion (normally with respect to one channel). Sometimes referred to as a 'pipe'.

Bipolar Transistor—A term used to denote the common two junction transistor types (NPN, PNP) as opposed to the field effect families of devices (JFET, MOSFET and so on.).

Bleeder—A resistive load across the output or filter of a power supply, intended to quickly discharge stored energy once the supply is turned off.

Circular Mils—A convenient way of expressing the cross-sectional area of a round conductor. The area of the conductor in circular mils is found by squaring its diameter in mils (thousandths of an inch), rather than squaring its radius and multiplying by pi. For example, the diameter of 10-gauge wire is 101.9 mils (0.1019 inch). Its cross-sectional area is 10380 CM, or 0.008155 square inches.

Core Saturation (Magnetic)—That condition whereby the magnetic flux in a transformer or inductor core is more than the core can handle. If the flux is forced beyond this point, the permeability of the core will decrease, and it will approach the permeability of air.

Current (Amps)—Flow of electric charge.

DC-DC Converter—A circuit for changing the voltage of a dc source to ac, transforming it to another level, and then rectifying the output to produce direct current.

dBm—Decibel reference to 1 miliwatt; 0 dBm equals 1 miliwatt.

Fast Recovery Rectifier—A specially doped rectifier diode designed to minimize the time necessary to halt conduction when the diode is switched from a forward-biased state to a reverse-biased state.

Foldback Current Limiting—A special type of current limiting used in linear power supplies, which reduces the current through the supply's regulator to a low value under short circuited load conditions in order to protect the series pass transistor from excessive power dissipation and possible destruction.

Frequency—The rate at which the cycle repeats. Generally measured in cycles per second or Hertz (Hz).

Ground Fault (Circuit) Interrupter (GFI or GFCI)—A safety device installed between the household power mains and equipment where there is a danger of personnel touching an earth ground while operating the equipment. The GFI senses any current flowing directly to ground and immediately switches off all power to the equipment to minimize electrical shock. GFIs are now standard equipment in bathroom and outdoor receptacles.

Impedance—The opposition to an RF signal that causes part of that signal to be reflected back. The magnitude and phase angle of these reflections are determined by the characteristics of the input (or output) of the device being tested. Expressed in ohms.

Input-Output Differential—The voltage drop appearing across the series pass transistor in a linear voltage regulator. This term is usually stated as a minimum value, which is that voltage necessary to allow the regulator to function and conduct current. A typical figure for this drop in most three-terminal regulator ICs is about 2.5 V. In other words, a regulator that is to provide 12.5 V dc will need a source voltage of at least 15.0 V at all times to maintain regulation.

Inverter—A circuit for producing ac power from a dc source.

MTBF—Mean time between failures.

OHM—The standard unit of resistance, reactance and impedance.

Peak Inverse Voltage—The maximum reverse-biased voltage which a semiconductor is rated to handle safely. Exceeding the peak inverse rating can result in junction breakdown and device destruction.

Power Amplifier—Electronic equipment that increases strength of signals passing through it.

Power Conditioner—Another term for a power supply.

Radio frequencies (RF)—The range of frequencies that can travel through space in the form of electromagnetic radiation.

Regulator—A device (such as a Zener diode) or circuitry in a power supply for maintaining a constant output voltage over a range of load currents and input voltages.

Resonant Converter—A form of dc-dc converter characterized by the series pass switch turning on into an effective series-resonant load. This allows a zero current condition at turn-on and turn-off. The resonant converter normally operates at frequencies between 100 kHz and 500 kHz and is very compact in size for its power handling ability.

Ripple—The residual ac left after rectification, filtration and regulation of the input power.

RMS—Root of the Mean of the Squares. Refers to the effective value of an alternating voltage or current, corresponding to the dc voltage or current that would cause the same heating effect.

Series Pass Transistor, or Pass Transistor—The transistor(s) that controls the passage of power between the unregulated dc source and the load in a regulator. In a linear regulator, the series pass transistor acts as a controlled resistor to drop the voltage to that needed by the load. In a switch-mode regulator, the series pass transistor switches between its ON and OFF states.

SOAR (Safe Operating ARea)—The range of permissible collector current and collector-emitter voltage combinations where a transistor may be safely operated without danger of device failure.

Spike—An extremely short perturbation on a power line, usually lasting less than a few microseconds.

Surge—A moderate-duration perturbation on a power line, usually lasting for hundreds of milliseconds to several seconds.

Transient—A short perturbation on a power line, usually lasting for microseconds to tens of milliseconds.

Varistor—A surge suppression device used to absorb transients and spikes occurring on the power lines, thereby protect electronic equipment plugged into that line. Frequently, the term MOV (Metal Oxide Varistor) is used instead.

Volt-Amperes—The product obtained by multiplying the current times the voltage in an ac circuit without regard for the phase angle between the two. This is also known as the apparent power delivered to the load as opposed to the actual or real power absorbed by the load, expressed in watts.

Voltage Multiplier—A type of rectifier circuit that is arranged so as to charge a capacitor or capacitors on one half-cycle of the ac input voltage waveform, and then to connect these capacitors in series with the rectified line or other charged capacitors on the alternated half-cycle. The voltage doubler and tripler are commonly used forms of the voltage multiplier.

VSWR—Voltage Standing Wave Ratio. The ratio of the amplitude of the electrical field or voltage at a voltage maximum to that at an adjacent minimum.

Wavelength—A means of designating a frequency band, such as the 80-meter band.

Conversion Factors:

Greek Alphabet/Symbol Key:

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