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Albacom - Microwave & Power Supplies glossary Category: Electronics and Engineering > Microwave, power supplies Date & country: 11/12/2007, UK Words: 150

Current mode control
Power converter regulation technique which monitors and controls power circuit current as well as output voltage

Current limiting
A feature designed to prevent overload of a constant voltage power supply by enforcing a maximum limit on the output current delivered to the load

Crowbar
A protection circuit which rapidly places a low impedance path across the power supply output terminals whenever a fault condition is detected

Cross regulation
The effect of a load change to one output of a multiple output power converter on the regulation of another output

Creepage
The spacing, across or through insulation materials, between circuit elements intended to be isolated from one another.

Corona discharge
A controlled current breakdown, which takes place in air, between circuit nodes with a potential difference between them which is large enough to initiate ionisation of the air in between. Normally an unwanted problem in high voltage power supplies but can be created deliberately as part of a process e.g. electrostatic ozone generation. See Arc dis…

Constant voltage
A power supply that regulates voltage level regardless of changes in load resistance

Constant current
A power supply that regulates output current level regardless of changes in load resistance

Common mode noise
Noise voltages which are common to both the “supply� and “return� lines at either the input or the output of a power converter, usually measured with respect to ground

Collector
This is an electrode used to absorb the energy in the electron beam after it has traversed through the slow-wave circuit. Cooling is usually by means of pumped fluid, conduction to a baseplate or forced air depending on the customer requirements.

Closed loop control
Technique which regulates the output voltage (or current) of a power converter by comparing the voltage to be controlled with a precision reference and using the difference (error) signal to drive a corrective action at the power circuit.

Clearance
The spacing, in air, between circuit elements intended to be isolated from one another

Burn in
A test process, which operates new power converters at or near full load for an extended period to precipitate the occurrence of early failure due to manufacturing defects. See ESS

Bunching
This is any process that produces a velocity modulated electron beam due to acceleration or deceleration of individual electrons.

Bulk DC supply
The DC supply derived by rectifying an AC prime supply, which is used to provide power to an off-line converter switching circuit

Battery charger
A power converter designed for the specific purpose of charging a rechargeable battery

Battery back-up
Feature whereby a battery is incorporated into a power converter to enable operation of the outputs for a substantial period of time, without prime supply

Arc discharge
An uncontrolled high current breakdown (flashover) which takes place in air, between circuit nodes with a potential difference between them which is large enough to cause ionisation of the air in between. Normally associated with high voltage power supplies, although damaging arc discharges can also occur in low voltage supplies where large stored …

Amplitude Modulation (AM)
Modulation in which the amplitude of a wave varies with time. It is usually defined as the ratio of the modulation to the average amplitude in dB.

Ambient temperature
The still air temperature of the immediate environment around the power converter

AM-PM Conversion
The change in phase angle between the input and output RF signals as a function of drive level changes. Expressed in degrees per decibel (dB), AM/PM conversion arises from a slowing of the electron beam as electronic interaction increases when RF drive exceeds a level of about 20 dB below saturation drive.

Active ripple rejection
Feature which enables a power converter to control the ripple content of its output voltages using its closed loop control to counteract or suppress ripple, usually only at frequencies well below the switching frequency

AC-to-AC converter
A power converter which changes an AC input supply into a different form of AC output supply. e.g. 415V 50Hz 3-phase input, 30kHz 600V output

AC to-DC converter
A power converter which changes an AC input supply into one or more DC output supplies

AC (Alternating Current)
A current (or voltage) which reverses polarity on a periodic basis

Current-fed
Term applied to power converter circuits where the power being switched is at a constant current, normally derived from using an inductor in series with the DC voltage source

DC (Direct Current)
A unidirectional current or fixed-polarity voltage

DC bus
The DC supply from which the switching circuit in a power converter draws power

DC to-DC converter
Power converter that changes a DC input supply into one or more DC output supplies, normally at different voltages to the input and possibly isolated from it

De-rating
Operating a power converter at reduced output power (or with some other specified reduction in parameters) to improve reliability

Depressed Collector
When the Collector is held a potential between the cathode voltage and the microwave tube body, usually earth potential, then some of the kinetic energy of the beam can be returned to the power supply. This provides a valuable increase in Electrical Efficiency of the device. Several stages of depression with gradually increasing voltage can be used to further enhance efficiency.

Differential mode noise
Noise voltages which can be measured between the “supply� and “return� lines at either the input or the output of a power converter

Duty Ratio or Duty
The product of the Pulse Duration and the Pulse Repetition Frequency (PRF). This is also the ratio of the Output Power (Average) to the Output Power (Peak).

Dynamic load
A load that changes from one level to another on a periodic or random basis

Efficiency
The ratio of total output power to total input power, normally expressed as a percentage

Electrical Efficiency
The ratio of the average RF output power of a tube to the total dc input power.

Electron Gun
This uses a Thermionic Cathode and associated Electron Optics to provide a laminar stream of electrons. The electron beam can be switched by means of a Control Grid. To reduce current to this grid a Shadow Grid is usually used to limit electron emission from the cathode behind the control grid.

Electron Optics
This is the arrangement of electrostatic and magnetic fields used to produce and focus an electron beam from a Thermionic Cathode.

EMC filter
A filter circuit designed to control conducted EMI and to enable conformance with EMC requirements

EMI (Electro-Magnetic Interference)
Also called radio frequency interference (RFI). EMI is unwanted conducted or radiated emissions from a power converter which leads to unacceptable interactions with load or input supply circuits

Filter
A frequency sensitive network, consisting normally of inductors and capacitors, that attenuates noise and ripple components of a DC rectified output, or EMI components which might affect an input supply

Flashover
An arc discharge through air around or over the surface of insulating materials, between parts at different potential or voltage. See Arc discharge

Flyback converter
A switching power converter using a single semiconductor switch in conjunction with an inductor or transformer. Operates by storing energy during the switch conduction time and releasing it when the switch is not conducting

Forward converter
A switching power converter using a single semiconductor switch in conjunction with a transformer. Operates by passing energy to the load during the switch conduction time

Frequency Pulling
For an oscillator, this is the change in the generated frequency caused by a change in the load impedance.

Frequency Pushing
For an oscillator, this is the change in frequency due to a change in the supply current (or voltage).

Full bridge converter
A switching (forward) power converter using 4 semiconductor switches configured as a bridge circuit. Operates by commutating an input DC supply to produce an AC drive voltage, with a peak-to-peak value equal to twice the DC supply voltage, to the primary of a transformer

Full wave rectifier
2-diode or 4-diode rectifier circuit that permits utilisation of the positive and negative half-cycles of an AC voltage

Gain
A general term used to denote an increase in signal power in transmission from one point to another. Usually expressed in dB, for a microwave tube the power gain is the ratio of the output signal power to the drive signal power.

Gain Equaliser
A device which can be used to modify the input signal to a Travelling Wave Tube to improve the Instantaneous Bandwidth by preferentially attenuating the mid-band frequencies and hence boosting the band edges.

Half bridge converter
A switching (forward) power converter using 2 semiconductor switches in conjunction with 2 capacitors or 2 diodes. Operates by commutating an input DC supply to produce an AC drive voltage, with a peak-to-peak value equal to the DC voltage, to the primary of a transformer

Half wave rectifier
Single diode rectifier circuit that permits utilisation of only positive OR only negative half-cycles of an AC voltage

Harmonic distortion
The presence of any unwanted frequencies which are harmonically related to the intended fundamental frequency in an AC voltage or current

Heater Surge Current
The maximum instantaneous current flowing through the cathode heater when cold and thus when the impedance is lowest.

Helix Slow-Wave Structure
This Slow-Wave Structure uses a simple helix, usually made from Molybdenum or Tungsten tape. This type of structure provides the maximum bandwidth, several octaves can be available in an appropriately designed travelling wave tube.

Holdup time
The time for which a power converter`s output voltage can be maintained following the loss or removal of input power. Usually achieved using energy stored in capacitors. See Battery back-up

Input voltage range
The range of input supply voltage for which the power supply meets its specifications

Inrush current
The greater-than-normal surge of input current that occurs in off-line switching power converters at initial power-up. Caused by the charging of the input filter capacitors

Instantaneous Bandwidth
The instantaneous electronic bandwidth of a microwave tube is the range of frequencies for which the output power is greater than a specified level.

Intermodulation
The modulation of different frequencies by each other, resulting in waves having frequencies equal to the sums and differences of integral multiples of the original frequencies.

Intermodulation Distortion
Distortion resulting from Intermodulation. Odd order intermodulation products can an important fraction of the output signals of an amplifier with the third-order product being the highest level.

Inverter
A power converter which changes DC input power into AC output power

Ion pump
An electronic vacuum pump used to help maintain or check the vacuum in a microwave tube.

Isolated converter
A power converter configured to isolate its prime supply from its output voltages, usually achieved using a transformer.

Isolation
Electrical separation between two circuits, or circuit elements

Line regulation
The change in output voltage due to the input voltage varying over its specified limits

Line voltage
RMS voltage of the AC prime supply used to power an off-line converter

Linear regulator
A form of voltage regulator where a dissipative active device such as a transistor is placed in series or parallel with the load. See Series regulator, Shunt regulator

Lineariser
A device which can be used to modify the input signal to a Travelling Wave Tube to improve the Intermodulation Distortion performance at close to saturation operation.

Load regulation
The change in output voltage due to the load current varying over its specified limits

Mains supply
Any prime supply which comes directly from the available power utility supply network e.g. 220V 50Hz in Europe, 110V 60Hz in the US

Microwaves
Electromagnetic waves whose frequencies lie between the far infrared and some lower frequency limit. Although not clearly bounded, the microwave region is commonly regarded as lying between 300 MHz and 300 GHz.

Multiple output supply
A power supply that delivers two or more output voltages

Noise
Noise is any unwanted periodic or random deviation in the output voltage (or the supply current) of a power converter. See Ripple

Noise Figure
The ratio in decibels of the total output noise produced by an amplifier to the noise that would be present at the output when the source temperature is 290 ºK.

Non-isolated converter
A power converter designed with a direct connection between its prime supply and its output voltages.

Off-line converter
Generic term for any power converter taking its input power directly from the utility (mains) supply network

Output Power (Average)
The power delivered to the load averaged over time. Usually the Output Power (Peak) multiplied by the Duty Ratio.

Output Power (Peak)
The power at the maximum of a pulse of power, excluding spikes.

Output Power (Saturation)
The maximum output power of an amplifier. If the input power required to achieve this level of output power is increased the this will produce a reduction off output power.

Overshoot
The amount by which an output exceeds its intended value at initial power-up or in response to a step change in load or input voltage

Perveance
Is a measure of the relationship between the beam current and voltage of an electron beam. It is defined as the ratio of the cathode current to the 3/2 power of the anode voltage. Due to the size of this unit the normal unit used is the microperv.

Phase Modulation (PM)
Modulation in which the phase angle of a wave varies with time.

Phase Shift
The phase difference between the output carrier wave and the input carrier wave, usually measured between small signal operation (10 dB or more below saturation) and saturated operation. Phase shift is a measure of tube linearity.

Polarity
Defines whether the output voltage of a DC power supply is “positive� or “negative� going with respect to its return

Post regulator
An additional voltage regulator circuit, usually a linear regulator, that provides improved regulation performance for the output(s) of a power converter

Power conditioner
Another term for power converter

Power converter
Electronic circuit designed to change electrical power from oneform into another e.g AC-to-DC, low voltage to high voltage etc

Power density
Indicative “figure of merit� relating the total power output capability of a power converter to its packaged volume, often in watts per cubic inch. Can providean easy comparison between power converters of similar capability but can be very misleading if used to compare units whose capabilities are very different.

Power factor
Conventionally taken to be the ratio of actual power (watts) to the apparent power (VA product) in an AC circuit. When related to power converters, power factor is used as a measure of the extent to which AC input supply currents are maintained in phase with the supply voltage. Power factor of 1 means that input supply current and voltage are exact…

Power factor correction
Any power converter technique which ensures that the current drawn by an AC-input converter from its input supply, is always in phase with the supply voltage and of the same form, normally sinusoidal

Power supply
Another term for power converter

Pre regulator
An additional voltage regulator circuit that provides a controlled input supply to a power converter. Used where the regulation performance of the basic power converter is inadequate for the application

Prime supply
The input supply, of any form, which provides power to the converter, and from which all other voltages are derived

Pulse
Momentary flow of energy of such short time duration that it may be considered to be an isolated phenomenon.

Pulse Duration
The time interval between the beginning and end of a Pulse at which the amplitude reaches a stated fraction of the peak pulse amplitude.

Pulse Repetition Frequency
The number of pulses per second.

Push pull converter
A switching (forward) power converter using 2 semiconductor switches to alternately drive the opposing primaries of a centre-tapped transformer

Pushing Figure
In an amplifier this is the rate of frequency for a variation in one of the control electrodes voltage of current. It is usually expressed in dB/volt or dB/amp.

PWM (Pulse Width Modulation)
A control technique for switching power converters where the conduction time (pulse width) of the semiconductor switches is modulated to control power transfer and thus regulate output voltage(s)