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Types of Power Problems
Brownout or voltage
fluctuation - Condition during peak usage
periods when electric utilities reduce their nominal line voltage 10% to 15% or
when load or line disturbances cause unwanted reductions in the line voltage.
A line interactive UPS copes with a brownout by using a preset voltage threshold to determine when to switch to batteries. In many cases this needlessly cycles the batteries. The line interactive unit must then switch back to commercial power, also based on some threshold - hopefully after the brownout is over. The load may be protected from the brownout, but at what cost?
See the complete comparison chart here!
SANUPS "on-line" double conversion technology provides true sine wave AC power continuously from the DC source. If a brownout is severe enough, the SANUPS may need to draw power from the batteries, but in many cases the SANUPS can adapt to the decrease in voltage. Either way, the load is never affected.
Frequency deviation -
All the utilities in the US, and those in many other countries provide AC at 60
Hertz frequency, some other countries have standardized on 50 Hertz. While
deviations from the chosen standard are generally not a problem with commercial power,
they can be an issue with engine driven generators.
Momentary power failure - Short outages caused by lightning,
transformer failure, etc. All UPS technologies can help protect against
momentary power failures, however:
Noise - The
aperiodic, random component of undesired deviations in voltage. Usually
specified in combination with ripple (the more periodic component).
See the complete comparison chart here!
Ambient temperature:
The temperature of the environment surrounding a power supply, generally assumed to be room temperature.
Bridge:
(1) Rectifier circuit incorporating four diodes (full-bridge) or two diodes (half-bridge) . (2) Converter or chopper section of switching power supplies incorporating four transistors (full-bridge) or two transistors (half-bridge) .
Brownout:
Condition during peak usage periods when electric utilities reduce their nominal line voltage 10% to 15% or when load / line disturbances cause unwanted reductions in the line voltage.
Brownout protection:
The ability of a UPS to provide constant AC output within specification through the duration of a brownout.
Chopper:
See Inverter
Commercial Power
The power supplies by local utility companies. The quality of commercial power in the US varies drastically depending on location, weather, and other factors.
Convection:
The transference of thermal energy in a gas or liquid by currents resulting from unequal temperatures.
Converter:
(1) A device that delivers dc power when energized by a dc source. (2) Sections of a switching power supply that perform the actual power conversion and final rectification.
Cooling:
Removal of heat. It can be accomplished using radiation, convection, forced air, or liquid means.
CSA (Canadian Standards Association):
An independent Canadian organization testing for public safety, similar to the function of UnderwritersELaboratories in the United States.
Derating:
A reduction of some operating parameter to compensate for a change in one or more other parameters. In power systems, the output power rating is generally reduced at elevated temperatures.
Double Conversion or On-line Operation:
A superior method of providing UPS back-up power. Incoming AC is converted to DC and then back to AC. The DC buss keeps the batteries toped off, and the inverter section provides true sine wave AC output regardless of the input. If the input voltage falters, there is no effect on the output - DC (now from the battery) is still being converted to AC.
Efficiency:
The ratio of output power to input power. It is generally measured at full-load and nominal line conditions.
EMI (electromagnetic interference):
Also called radio-frequency interference (RFI), EMI is unwanted high-frequency energy caused by switching transistors, output rectifiers, zener diodes, etc. EMI can be conducted through the input or output lines or radiated through space.
Faraday shield:
An electrostatic shield would on a transformer, designed to reduce interwinding capacitance. The result is less common-and differential-mode noise at the output of the power supply.
Federal Communications Commission (FCC):
United States federal regulating body whose new EMI limitations are affecting the design and production of digital electronics systems and their related subassemblies.
Filter:
A frequency-sensitive network that attenuates unwanted noise and ripple components.
Full-wave rectifier:
Rectifier circuit that rectifies both halves of an ac wave .
Ground loop:
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 one circuit may be capacitively, inductively, or resistively coupled into the other circuits via the common line.
Heat sink:
Device used to conduct away and disperse the heat generated by electronic components .
Inrush current:
A high surge of input current that occurs in switchers and occasionally in linears upon initial turn on .
Inverter:
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.
Isolation:
The degree of electrical separation between two points. It can be expressed in terms of voltage (breakdown), current (galvanic), or resistance and/or capacitance (impedance). In power supplies, the input-to-output isolation is important to maximize.
Leakage current:
Current flowing between the output buses and chassis ground due to imperfections in electronic components and designs. It must be tightly controlled to satisfy safety regulations such as UL and VDE.
Line regulation:
The variation of an output voltage due to a change in the input voltage, with all other factors held constant. Line regulation is expressed as the maximum percentage change in output voltage as the input voltage is varied over its specified range.
Line regulator:
Power-conversion equipment that changes the degree of regulation, filters noise, and/or changes the voltage of incoming ac power.
Load:
The equipment to be powered by the output.
Master:
The unit in a master-slave system of interconnection that exercises control over the outputs of one or more slave units. Such a system is a common technique used to ensure load sharing of parallel operating power systems.
Modular:
A physically descriptive term used to describe a UPS made up of a number of separate subsections. Modular construction tends to lower the MTTR.
MTBF (mean time between failures):
A measure of reliability. The reliability interval calculated in accordance with the procedures of MIL-HDBK 217.
MTTR (mean time to repair):
The average time required to repair a piece of equipment. It is a result of both electrical and mechanical design factors.
Noise:
Noise is the aperiodic, random component of undesired deviations in output voltage. Usually specified in combination with ripple.
Nominal output voltage:
The intended, ideal voltage of any given output.
Operating temperature:
The range of temperatures within which equipment will perform within specified limits.
Opto-isolator:
Device that provides electrical isolation and a signal path by making an electrical to optical to electrical signal transformation. This is accomplished with a light-emitting diode in close proximity to a phototransistor.
Parallel operation:
The ability of UPSs to be connected so that the current from corresponding outputs can be combined into a single load.
PARD:
Acronym for "periodic and random deviation" and used as the specification term for ripple and noise. Ripple is the unwanted portion of the output harmonically (periodically) related in frequency to the input line and to any internally generated switching frequency. Noise is the unwanted, aperiodic output deviation.
Peak transient output current:
The maximum peak current that can be delivered to a load during transient loading conditions, such as inrush.
Phase-controlled modulation:
A circuit used in switching regulators where the operating frequency is held constant (typically 60-Hz line frequency) and the phase angle at which the control elements are turned on its varied, controlling both line and load changes with minimal dissipation .
Pin fins:
Type of heat sink that uses pins in place of conventional extruded fins .
Power conversion:
The processing of medium-quality electric power delivered by utilities to make it compatible with the needs of sensitive electronic circuits .
Power factor:
The ratio of actual power used in a circuit to the apparent power. Power factor is the measure of the fraction of current in phase with the voltage and contributing to average power.
Power supply:
The common term for electronic devices that provide dc output voltages when powered by an ac primary source.
Pulse-width modulation (PWM):
A circuit used in switching regulated power supplies where the switching frequency is held constant and the width of the power pulse is varied, controlling both line and load changes with minimal dissipation .
Redundancy:
The ability to connect units in parallel so that if one fails the other(s) will provide continual power to the load. This mode is used in systems when power failure cannot be tolerated .
Response time:
The amount of time it takes for an output to react to a dynamic load change and settle within some tolerance band following the load change.
RFI (radio-frequency interference):
See EMI.
Ripple:
The periodic noise component of the power output voltage. See PARD.
Short-circuit protection:
See Current limiting circuit.
Slave:
The unit in a master-slave paralleling scheme that is controlled by the master unit. See Master.
Snubber:
A network containing a resistor, capacitor, and diode used in the switching power supplies to trap high-energy transients and protect sensitive components.
Static load:
A load that remains constant over a given time period. It is usually specified as a percentage of full load.
Step change:
An abrupt and sustained change in one of the influence or control quantities (e.g., load current).
Stress-aging:
The process of subjecting a new electronic device to a variety of stresses to force the occurrence of all burn-in failures .
Switching frequency:
The rate at which the source voltage is switched in a switching regulator or chopped in a dc-to-dc converter.
Switching regulator:
A high-efficiency dc-to-dc converter consisting or inductors and capacitors to sort energy and switching elements (typically transistors or SCRs), which open and close as necessary to regulate voltage across a load. The switch duty cycle is generally controlled by a feedback loop to stabilize the output voltage.
Temperature coefficient:
The average percent of change in output voltage per degree change in temperature with load and input voltage held constant.
Thermal protection:
Protection via a thermally actuated switch that interrupts the operation of a device if the internal temperature exceeds a predetermined value.
Thermal regulation:
Monitoring the temperature of the batteries to assure proper charging.
Transformer:
A magnetic device that converts ac voltages to ac voltages at any level. An ideal transformer is a lossless device in which no energy is stored and that requires no magnetic current.
Transient:
A temporary and brief change in a given parameter. Typically associated with input voltage or output loading parameters .
Transient response time:
The amount of time taken for an output to settle within some tolerance band, normally following a stated change in load.
UL (UnderwritersELaboratories):
An independent, not-for-profit organization testing for public safety in the United States. UL recognition is required for equipment used in some applications .
Undershoot:
The amount by which an output falls below its specified value in response to a rapid load change.
UPS (uninterruptible power supply):
A device designed to supply power in the event of temporary or permanent loss of ac line power. Often these supplies will operate with either an ac line input or dc battery backup input.
VDE (Verband Deutscher Elektrotechniker):
A West German organization testing for public safety; similar to UL in the United States.
Power Systems Division
Sanyo Denki America, Inc.
468 Amapola Avenue
Torrance, CA 90501
Tel: (310) 783-5400
Fax: (310) 782-8021
power@sanyo-denki.com
