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Automatic Crossover |
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The characteristics of a Power Supply that automatically changes the method of regulation from voltage to current or current to voltage as dictated by the load condition. |
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Bleeder Resistor |
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A resistor usually connected across a filter circuit to help with regulation and used to discharge capacitors in filter circuits when the unit is de-energized. |
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Brown-Out |
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Condition during peak loading periods when electricity suppliers reduce the nominal voltage approximately 10 to 15 per cent. |
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Common Mode Noise |
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Common mode Noise is that component of noise which is common to both the DC outputs and return line, with repect to an electrically fixed point. |
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Constant Current |
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A power supply which regulates for current regardless of load resistance changes. |
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Converter (DC/DC-Converter) |
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A device that delivers DC power when energized from a DC source. AC is generated as an intermediate step in the DC to DC process. Rectification of an inverter output results in DC to DC converter. |
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Cooling |
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The removal of the heat which in a Power Supply is generated by the transformer, rectifiers, filters, power switches, and other parts of the circuit. The Power Supply cools by radiation, convection (both natural and / or blower aided) and conduction to an external heat sink. |
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Cross Regulation |
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In a multiple output Power Supply, the load variation of one output can cause a voltage variation in other outputs. This voltage shift, divided by its nominal output voltage, is cross regulation. |
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Crowbar |
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A means by which Power Supply's output is electrically short circuited, preventing over-voltage damage to the load in the event of Power Supply failure. Usually, when the output voltage exceeds a prespecified level. This, in turn, activates the Power Supply short circuit protection, preventing supply destruction. See also Overvoltage Protection. |
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Derating |
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A reduction of some operating parameter to compensate for a change in one or more other parameters.. |
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Differential Mode Noise |
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That part of noise voltage measured with respect to output return. This does not include common mode noise, and is most accurately described as a voltage source. |
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Drift |
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The amount by which the output voltage charges, over long periods of time, all other factors remaining constant. |
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Efficiency |
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The ratio of output power to input power. This is generally measured at full load with nominal line conditions. In a multiple output switching power supply, efficiency is a function of total output power and the particular division of power among the lower voltage and higher voltage outputs. |
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EMI (RFI) |
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Electromagnetic Interference (Radio Frequency Interference) is unwanted high frequency energy. EMI can be conducted through the input or output lines, or radiated through space. Conducted EMI (RFI) can be reduced using proper filtering. Radiated EMI (RFI) can be reduced by judicious board layout and enclosing the supply in a metal enclosure. |
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ESR (Equivalent Series Resistor) |
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The amount of resistance in series with an ideal (lossless) capacitor which exactly duplicates the performance of a real capacitor. In general, the lower the ESR, the better the quality of capacitor and the more effective it is as a filtering device. ESR is a prime determinant of ripple in switching supplies. |
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Fall Time |
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See "Rise Time and Fall Time". |
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Faraday Shield |
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An electrostatic shield wound on a transformer, designed to reduce interwinding capacitance. The effect of this is to reduce output common and differential mode noise. |
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Feedback |
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The connection of the output of a control circuit back to its input to obtain a desired operational characteristic |
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Ground Loop |
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A feedback problem caused by two or more circuits sharing a common electrical line, usually a common ground line. Voltage gradients in this line caused by the first circuit may be resistively, inductively or capacitively could into the other circuit via the common line. With power supplies, this problem can be reduced using single point grounding near the supply. |
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Heat Sink |
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A device used with semiconductors to absorb, conduct away, and to disperse the heat they generate. |
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Hold up Time |
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The total time any output will remain within its regulation band after line input voltage has suddenly dropped to zero. ELBA specifies hold up at full load and nominal line conditions. |
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Inhibit |
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The ability to turn off the outputs of a power supply from a remote location. |
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Input Surge Current |
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The peak line current which flows during turn-on. Surge current is caused by the charging of the input capacitor, and limited only by the input impedance. This surge current is limited by adding a circuit specifically designed to have high initial impedance. This limiting is usually achieved with a thermistor, SCR or resistance circuit. |
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Inverter |
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A device that delivers AC power when energized from a source of DC power. Inverters may be frequency, amplitude or pulse width modulated to vary output voltage. |
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Isolation Voltage |
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The maximum voltage by which any part of the circuit can be operated away from chassis ground. Also the maximum voltage between any output and input terminal. |
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Line Regulation |
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The variation of an output voltage due to a change in line input voltage, with all other factors held constant. Line regulation is expressed as the percentage change in output voltage as the line input is varied over its entire range. |
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Line Frequency Regulation |
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The variation of an output voltage due to change in line input frequency, with other factors held constant. This effect is neglegible in switching and linear supplies, but is critical in ferroresonant supplies. |
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Load Regulation |
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The variation of an output voltage caused by a change in that output's load, with all other factors held constant. |
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Logic Enable |
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The ability to turn a power supply on and off with a TTL signal. A logic low turns the supply off. A logic high turns the supply on. |
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Logic High |
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A voltage of greater than 2,3V with a maximum of 5,5 volts. Also known as a logic "1". TTL compatible. |
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Logic Inhibit |
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The ability to turn a power supply off and on with TTL signals. A logic low allows the power supply to operate. A logic high turns off the power supply. |
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Logic Low |
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A voltage less than 0,8V. Also known as a logic "0". |
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Mean Time Between Failure (MTBF) |
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A measure of reliability. The average time between failures of a supply during the portion of its life at the bottom of the "Bath tub cume. MTBF can be either observed or calculated by summing the reciprocal failure rates of individual components. |
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Noise and Ripple |
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See Ripple and Noise |
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Nominal Output Voltage |
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The specific voltage a power supply is designed and set to which is usually an average of the maximum amd minimum range. |
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Open Frame Construction |
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A construction technique common in OEM power supplies where the power supply is not provided with an enclosure. |
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Output Impedance |
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At any frequency of load change, Z out = E out/I out. The output impedance of most supplies increases with output frequency. (The output impedance of an ideal voltage power supply would be zero at all frequencies). Output impedance is usually a function of amplifier gain, output capacitance, internal resistance and output circuit inductances and bandwidth. |
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Output Transient Response Time |
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The time taken for any output to settle to within the some tolerance band, normally following a stated change in load. |
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Overcurrent Limiting |
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A protection mechanism which limits the output current. |
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Overshoot |
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The amount by which an output exceeds its final value in a transient reponse to a rapid change in load or input voltage. In power supply design this parameter is particularly important at turn-on. |
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Overvoltage Protection |
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A protection mechanism for the load which does not allow the output to exceed a pre-set level. In most cases, the input power must be recycled to restore the power supply output. |
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Parallelability |
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The ability of a supply to be connected so that the currents from corresponding outputs can be summed to others space together into a single load. |
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Pass Transistor |
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Power transistor in a linear power supply. This element is in series with the load. The current to the load must pass through this device. |
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Peak Charging |
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A rise in voltage across a capacitor caused by the charging of the capacitor to the peak rather than RMS value of the input voltage. This generally occurs when a capacitor has a high discharge resistance across it and large ripple or spikes on its input line. In a switcher this effect determines minimum load (discharge resistance) conditions on each output to maintain regulation. |
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Peak Transient Output Current |
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The maximum peak current that can be delivered to a load during transient conditions. |
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Polarity |
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The ability of a power supply to operate either above or below ground (see isolation voltage) up to a specific voltage. |
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Post Regulator |
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A linear (dissipative) regulator used on the output of a switching supply to further improve overall regulation performance of the supply. Post regulators can be either the 3 terminal I.C. type or a custom discrete design. Since the differential voltage across the post regulator can be kept to a minimum dissipative losses are generally small. |
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Power Factor Cos - phi |
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The ratio of the actual power used in a circuit to apparent power. |
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Power Fail Detect |
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An option which senses the DC voltage across the input capacitors. Should the line fail, it senses an abnormally low DC level across the capacitors and provides an isolated TTL signal output. |
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Power Foldback Protection |
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See Short Circuit Protection |
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Primary Components |
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A collective term generally refering to all components on the primary side of the output transformer |
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Pulse Loading |
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See Peak Transient Output |
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Pulse Width Modulation |
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A method used in regulating switching type power supplies where the switching frequency is held constant and the width of the pulse is varied, controlling both line and load changes. |
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Redundant |
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The ability to connect power supplies in parallel so if one fails the other will automatically switch on providing continual power to the load. This mode is used when power supply failure can not be tolerated. |
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Regulator |
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The part of a power supply which controls the output voltage. In most cases, the regulator acts to stabilize the output voltage at a pre-set value. |
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Remote Sensing |
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A method of sensing the output voltage at the load, rather than at the output terminals of the power supply. By providing separate voltage sense leads to the regulator, voltage errors caused by IR drops in the load carrying line can be eliminated for the sensed output. This is rarely used in switchers because it can cause control loop instability. |
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Remote Turn On |
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A mechanism to activate or disable the supply, while line power is on, by means of an external switch. |
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Remote Voltage |
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The ability to be able to change the output voltage of a power supply at a remote location. |
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Return |
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An arbitrary name for the common terminal for all outputs. It carries the return current of all the outputs. |
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Rise Time and Fall Time |
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When applied to the switching transistor, that time in which non-zero currents and voltages result in high peak power dissipation. Careful attention must be paid to reducing these times, particularly when switching inductive loads. |
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Ripple and Noise |
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Ripple is that unwanted portion of the output harmonically related in frequency to the input power and to any internally generated switching frequency. Noise is unwanted, unprogrammed aperiodic output deviation. |
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Short Circuit Protection |
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An overload protection method where output voltage and current decrease simultaneously as the load increases past a given point and begins to approach a short circuit. Also known as output short circuit protection. |
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Temperature, Ambient |
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The room temperature or temperature of the still air surrounding the power supply, with the supply operation. Measured roughly ½ inch horizontally from the supply in still air (not forced air).. |
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Temperature Coefficient |
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The average per cent change in per degree change in temperature with load and input voltage held constant. The coefficient is usually derived from output voltage measurements taken at room temperature (+20°C) and at two specified operating extremes. |
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Temperature, Operating |
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The range of temperature that can not be exceeded when operating the power supply. |
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Temperature, Storage |
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The range of temperatures within which the supply may be stored (not operated) with no resulting degradation in performance. |
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Thermal Protection |
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Protection via a thermally operated switch which will shutdown the power supply if the heat sink temperature exceeds a certain value. |
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Warm Up Drift |
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The change in output voltage which occurs during warm up, from turn on of a cool supply until about 30 minutes after turn on. Warm up drift is measured at constant ambient temperature, and is primarily due to internal components reaching thermal equilibrium. |
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Warm Up Time |
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The time needed, after turn on, for the supply to reach thermal equilibrium with a constant load and no drafts. This time is usually no more than 30 minutes. |
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