DC/DC Terminology

Application Note - Interpoint
Crane Aerospace & Electronics Power Solutions
DC/DC Terminology
Crane Aerospace & Electronics Power Solutions
DC/DC Terminology
Application Note
Although the concepts stated are universal, this application note was written specifically for Interpoint products.
This application note defines some of the common terminology
used to describe the characteristics and operation of DC/DC
converters.
Absolute Maximum
The maximum condition which the power converter can withstand
without permanently damaging the device. Usually applied to
input voltage, output current/power, or case temperature.
Aging
The long term change in output voltage of a power supply over
time with all other factors held constant, usually accelerated
by temperature. Long term aging is most often expressed as a
percentage per 1000 hours and short term aging as a percentage
over the first 24 hours of operation.
Ambient Temperature
The temperature in the medium around a component and is
measured some distance from the device (usually 0.5 inches) to
be considered uniform. Temperature ratings for converters are
usually given for case temperatures (Tc). The case temperature
for an operating converter is ordinarily higher than the ambient
temperature.
Balun
An inductor used for impedance matching between a BALanced
line and an UNbalanced line. It presents a high impedance to
common mode signals and a low impedance to differential mode
signals. A balun is sometimes used in series with the input line
of switching power converters to suppress common mode noise
currents.
Boost Converter – Topology
The boost circuit is a commonly used building block in converter
design. The switch controls energy transfer from the input
source, through the inductor, to the load. The output-to-input
voltage ratio, is always greater than one and is ideally equal to
the inverse of one minus the duty conduction cycle of the switch
during continuous operation. The boost topology also requires an
output energy storage capacitor to support the load current while
the switch is on.
Buck Converter – Topology
The buck circuit is another commonly used building block in
converter designs. In its basic form, without a transformer, the
output voltage is always less than the input voltage. When the
transistor is switched on, energy is transferred from the input
source to the inductor and the output. When the switch is turned
off, the inductor current ramps downward and the energy is transferred to the output capacitor and the load. The output-to-input
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voltage ratio is ideally equal to the conduction duty cycle of the
switch for continuous operation. Since most applications severely
limit the amount of pulsating current that can be drawn from the
converter’s input source, some form of low pass filter is generally
inserted on the input side of the switch.
Case Temperature
The temperature of a converter measured at its baseplate.
Temperature ratings for converters are usually given for the
case temperature (Tc). The case temperature for an operating
converter is ordinarily higher than the ambient temperature.
Classical Converter – Topology
(See Royer converter)
Common
The common input or output terminal of a power supply. It carries
the return current for the terminals. Also referred to as “return”.
Common Mode Noise
The component of noise which is common to both the DC input
and input return or output and output return with respect to a
common reference. The common reference is generally the
converter’s metal base.
Constant Voltage Power Supply
A power supply that regulates its output voltage within
specified limits in spite of line, load, and temperature changes.
Cross Regulation
On multiple output power supplies, the change (usually measured
in percentage) of the nominal output voltage on one output while
the load is varied on another output over specified conditions.
Crowbar
An overvoltage protection circuit which monitors the output
voltage of a power supply and rapidly creates a low resistance path across the output when a predetermined voltage is
exceeded.
Derating
with
Case Temperature
The specified reduction in output power/current as a function
of case temperature above the maximum full load rated case
temperature.
Dielectric Breakdown Voltage
The minimum AC or DC voltage which, when applied across an
isolation barrier of a power converter, can cause a direct short
to the outputs or the case. Input to output and input/output to
case are examples of isolation barriers. Exceeding a converter’s
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DC/DC Terminology
Application Note
dielectric breakdown voltage can permanently degrade performance.
Differential Mode Noise
The component of noise measured from the DC output or input to
the return.
Driven Push-Pull Transformer – Interpoint Topology
The driven push-pull circuit is derived from the Royer converter.
Instead of relying on transformer saturation to provide the
switching action, the driven converter uses a multivibrator to
drive the switching transistors at a frequency chosen to maximize
efficiency and minimize transformer size. Like the Royer, output
voltage is directly proportional to input voltage. Efficiencies are
typically higher than the Royer due to the non-saturating nature
of the transformer switching action. This topology is used in
Interpoint’s DCH Series of isolated, unregulated converters.
Drift
The change in output voltage over a period of time with all other
operating parameters held constant.
Dual Balanced Outputs
An output voltage regulation scheme for dual opposite polarity
output converters in which the absolute sum of the two voltages
is held constant.
Dynamic Load Regulation (Output Impedance)
The ratio of change in transient output voltage to change in load
current.
Efficiency
The ratio of power delivered to power consumed, expressed as a
percentage.
EMI (Electromagnetic Interference)
Conducted or radiated noise which is emitted from switching
power supplies.
Epoxy Potting
An inexpensive method of hybrid packaging which consists
of coating the substrate with a conformal coating and then
submerging it in a potting cup filled with epoxy. Epoxy-potted
modules have excellent thermal capacity characteristics but are
not as resistant to moisture or as tolerant of temperature cycles
as other types of packaging.
ESR (Equivalent Series Resistance)
Faraday Shield
An electrostatic shield between the input and output windings of
a transformer. The shield reduces capacitive currents and output
common mode noise by shorting capacitive currents to a fixed
reference, usually the case ground.
Fault Mode Input Current
The input current of a DC/DC converter with the output terminals
shorted.
Flyback Converter – Topology
In the basic flyback converter when the transistor is turned on,
the current increases linearly in the transformer primary. When
the switch turns off the decreasing flux in the transformer core
causes a current to flow in the secondary, transferring energy to
the output capacitor and the load. Since the transformer assumes
the roles of both an energy storage device and a transformer,
only one magnetic component is needed.
Foldback Current Limiting
A short circuit protection system which decreases the output
current as the overload increases, with the output current
reaching a minimum at short circuit.
Ground Loop
An unwanted feedback voltage caused by two or more circuits
sharing a common electrical ground or return line.
Hermetic Seal
A sealing technique sometimes used for microcircuit packages to
provide airtight and moisture resistant components. The highest
quality hermetically sealed converters have final soldering or
welding performed in a dry nitrogen environment and undergo
leak testing. Hermetically sealed packaging increases a converter’s reliability and extends its life.
Hi-Pot Test (High Potential Test)
A test performed by applying a high voltage between isolated test
points in order to test the minimum specified isolation resistance
of a power supply.
Hold-up Time
The length of time a power supply will maintain its output voltage
within specifications after loss of its input power.
Idle Current
See Standby Current.
The amount of resistance, in series with an ideal capacitor,
required to exactly model a real capacitor.
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Application Note
Input Line Filter
Isolation Voltage
Input/Output Capacitance
Leakage Current
Input Ripple Current
Line Regulation
A low pass filter at the input of a power supply which can attenuate input line noise fed into the supply or reflected line ripple
current generated by the supply. (See also Pi Filter.)
The effective barrier capacitance from the input pins to the output
pins.
The magnitude of the AC current generated at the input of a
DC/DC converter by the switching operation of the converter,
measured in milliamps peak-to-peak or milliamps RMS. Input
ripple current is usually measured at full load over a specified
bandwidth with a specified source impedance. (See also PARD.)
Input Ripple Current Filter
A filter at the input of a power converter designed to reduce the
ripple current generated by the switching action of the converter.
Input Ripple Rejection
The attenuation, in dB, of the output AC signal in response to the
injected AC input signal at a particular frequency or as a function
of frequency.
Input Transients
Temporary changes in the input voltage to a power converter
which may fall outside the minimum/ maximum input voltage
range of the converter. Those which exceed the maximum may
damage the converter.
Input Voltage Range
The input voltage range over which a DC/DC converter is guaranteed to meet its specifications.
Inrush Current
The peak instantaneous input current drawn by a power supply at
turn-on.
The AC or DC current flowing from input to output and/or case of
an isolated power supply at a specified voltage and frequency.
The change in output voltage (expressed in millivolts or
percentage of output voltage) as the input voltage is varied over
its specified range. Line regulation is usually measured at full
load.
Linear Regulator - Topology
A linear regulator is a circuit which uses an error amplifier to
compare a fraction of the output voltage with a voltage reference.
The amplifier output drives a series regulator transistor which
keeps the output voltage constant. Some linear regulators include
a short circuit protection circuit which senses the voltage across
a current sampling resistor. When this voltage exceeds a preset
level, the circuit reduces the base drive of the transistor and
limits the output current. Linear regulators are used in DC/DC
converters to regulate output voltages which are not controlled by
feedback loops, or to provide tight post-regulation.
Load Regulation
The change in output voltage (expressed in millivolts or
percentage of output voltage) as the load is varied from a specified minimum to full load. Load regulation is usually measured at
nominal input voltage.
Low Line Dropout Voltage
The low input line voltage at which an operating power converter’s output voltage will drop below the specified minimum output
voltage.
Maximum Allowable Voltage Between Pins
On power converters with output voltage trim and/or remote
sense, the maximum voltage that is allowed at the specified pins
due to the combined effects of line drops and voltage trim.
Inverter
A DC to AC power converter.
Isolation
The guaranteed maximum AC or DC voltage which can be
applied from input to output of a power supply while the supply
maintains the specified isolation resistance in megohms.
The electrical separation between the input, output and case of a
power supply. Isolation is usually expressed in megohms.
Maximum Output Current
The maximum steady-state current a converter is guaranteed to
supply while continuing to meet its other requirements.
MTBF (Mean Time Between Failures)
The failure rate of a power supply, calculated using MIL-HDBK217 for military or aerospace applications. MTBF calculations
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Application Note
(expressed in hours) vary widely depending on assumptions
made about the quality of components and assembly, number of
interconnects, packaging methods, case temperature, and operating environment.
Overload Protection
Nominal Clock Switching Frequency
Overvoltage Clamp
In a switching power converter, the frequency at which the power
switch chops the incoming DC voltage. The frequency is chosen
to optimize transformer efficiency and size.
Non-Saturating Core Circuit
A circuit design which controls the switching action of a power
converter so as to limit the operation of the transformer to the
non-saturating portion of its B (flux density) – H (magnetizing
force) curve.
Output Current Limiting
An output protection feature in which the output current is limited
to a predetermined maximum value under overload and/or short
circuit conditions.
Output Power
An output protection feature which limits the output current of a
power supply under overload conditions so that the supply will
not be damaged.
See Overvoltage Protection.
Overvoltage Protection
A feature which limits the output voltage or inhibits a power
supply when its voltage exceeds a specified level.
PARD (Periodic
and
Pi Filter
A filter consisting of two parallel capacitors (line to line) and a
connecting series inductance which is used at the input of a
switching power supply to reduce ripple current, or at the output
to reduce ripple voltage.
The maximum steady-state power (the product of voltage and
current) which the converter is guaranteed to be able to deliver to
the load while continuing to meet its other specifications.
Post-Regulation
Output Trim
Power Dissipation
On adjustable output power converters, the maximum allowable adjustment of the output voltage, often expressed as a
percentage of the nominal output voltage. Output trim is used
to compensate for resistance drops (Also referred to as “output
voltage adjustment”).
Output Voltage
The nominal DC voltage at the output terminals of a DC/DC
converter.
Output Voltage Adjustment
See Output Trim.
The magnitude of the AC voltage on the output of a converter,
measured in millivolts peak-to-peak or millivolts RMS over a
specified bandwidth. Usually measured at full load. (See also
PARD.)
(Total Error Voltage) The maximum deviation, in percentage of
nominal, of the output voltage under all specified minimum or
maximum conditions.
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Use of a linear regulator on the output of a switching power
supply to improve regulation and reduce ripple voltage.
The Sum total of all internal power losses defined as the difference between input power and output power. PD =(Pin-Pout)
Power Foldback
A power supply feature in which the input power is reduced to a
low value under overload conditions.
Pre-Regulation
The regulation at the input side of a power supply, usually by a
type of switching regulator or a linear regulator.
Pulse Width Modulation
Output Voltage Ripple
Output Voltage Tolerance
Random Deviations)
The sum of all ripple and noise components measured over a
specified bandwidth.
A method of controlling the power switches in a switching power
supply by varying the duty cycle of the switches while holding the
switching frequency relatively constant.
Push-Pull DC Transformer – Topology
The push-pull DC transformer is a commonly used switch, transformer, and diode topology. Its name is derived from the alternate conduction actions of the two primary side switches and
the secondary side rectifier elements. The alternate switching
actions of generate a symmetrical alternating voltage across
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the primary of the transformer. A corresponding AC voltage will
appear across the secondary which, when rectified, results in a
DC voltage at the output such that:
Vo is approximately Vs x (Ns/Np)
Quasi-Squarewave Converter – Topology
The quasi-squarewave converter is derived from the combination
of a buck converter and a push-pull DC transformer The operation is similar to that of the buck converter with switches alternately closing to transfer energy from the input through the transformer to the output inductors. As in the buck, the output-to-input
voltage ratio is proportional to the duty cycle of the switches.
Reference
A stable voltage, generally supplied by a voltage reference
IC, which is used for comparison to control a regulated output
voltage.
Regulated/Unregulated
A power converter’s output voltage is said to be regulated if
its value is constant within specified limits, regardless of input
voltage and load variations. An unregulated output voltage varies
in relation to changes in input voltage and load.
A method of regulating the output voltage of a power supply at
the load by using sensing leads which carry very little current,
thereby compensating for voltage drops in the load leads.
Resolution
For an adjustable power supply, the smallest change in output
voltage which can be realized by the adjustment.
Return
The common input or output terminal of a power supply. It
carries the return current for the terminals. Often referred to as
“common.”
Reverse Voltage Protection
A feature which protects a power supply against damage from a
reverse polarity voltage applied at the input or output terminals.
and
Noise
The Royer circuit is a self-oscillating, push-pull topology. The
transistors are driven from auxiliary windings on the transformer.
When the input voltage is applied, the bias circuit causes one of
the transistor switches to turn on. This switch remains on until
the transformer core saturates, thereby removing the base drive
from the conducting transistor. Residual energy in the core then
changes the polarity of the voltage across the windings which
turns on the opposing transistor. The circuit continues to selfoscillate at a frequency proportional to the input voltage, which
produces an output square wave of voltage which is rectified and
filtered to produce the output. Line regulation is not provided by
this circuit and the output voltage is directly proportional to the
input voltage. The primary advantage of the Royer circuit is its
simplicity, which keeps component and assembly costs down.
Its use is limited, however, to low power applications due to its
inherent low efficiency (typically less than 65%). Core magnetic
losses are especially large at the high oscillation frequencies
needed for small transformers.
Series Regulation
A method of linear regulation in which the control device is in
series with the supply and the load.
Short-Circuit Protection
Remote Sensing
Ripple
Royer (Classical) Converter – Topology
The magnitude of the AC voltage on the output voltage of a
power supply. This is the result of conducted line noise, internal
switching transients and other random noise.
A feature which limits the output current of a power supply under
short circuit conditions in order to prevent damage to the supply.
Shunt Regulation
A method of linear regulation in which the control device is in
parallel with the load.
Soft Start
A feature which limits the start-up current of a switching supply
and causes the output voltage to rise gradually to its normal
value.
Solder Sealing
A method of attaching a metal cover to a metal package base
which uses a low temperature alloy to fuse the cover-to-base
interface. Hermetically sealed converters are often solder sealed
in a dry nitrogen atmosphere.
Split Bobbin Winding
A method of winding a transformer in which the primary and
secondary are wound side by side on a bobbin with an insulation
barrier between the two windings.
Standby Current
The no-load or shutdown input current of a power supply.
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DC/DC Terminology
Application Note
Start-up Overshoot
The maximum deviation of the rising edge of a power supply from
its final, steady-state value following a release from inhibit condition.
Start-up Time
The maximum time required for the output voltage of a power
supply to reach a specified percentage of its final, steady-state
value, following a release from inhibit condition.
Switching Regulator
A circuit which chops and re-rectifies an input DC voltage, and
then uses a feedback control loop to regulate the output voltage
of a power supply. The feedback loop controls the pulse width
and/or frequency of the switching action.
Synchronization
A switching power supply feature in which the internal switching
frequency can be synchronized with an external clock within
specified limits.
a packaged module. The smallest and most reliable DC/DC
converters are made with thick film hybrid technology.
Topology
The basic configuration of a circuit.
See also the following basic topologies:
Boost Converter
Buck Converter
Flyback Converter
Linear Regulator
Push-Pull DC Transformer
Quasi-Squarewave Converter
Royer (Classical) Converter
And Interpoint topologies:
Driven Push-Pull Transformer
Feedback Controlled Flyback Converter
Pulse Width Modulated (PWM) Quasi-Squarewave Converter
Temperature Coefficient (of Voltage)
The maximum percent change in nominal output voltage per
degree centigrade change in case temperature over a specified
temperature range.
Temperature Range, Operating
The temperature range within which a power supply can be operated while meeting specified performance characteristics. The
operating temperature range is specified for case temperature
rather than ambient temperature.
Temperature Range, Storage
The ambient temperature range within which a power supply can
be stored with no subsequent degradation of its operating specifications.
Thermal Impedance
Thermal resistance. The measure of opposition to heat flow for a
particular material or materials (°C/W).
Tracking
A characteristic of multiple output power supplies in which one or
more output voltages follow another with line, load, and temperature.
Transient Recovery
The peak change in the output voltage of a power supply
following a step change in a load or line condition.
Transient Response
The time required for a converter’s output to return to within its
specified regulation range following a step change in line or load.
Undershoot/Overshoot
The time required for a converter’s output to return to within its
specified regulation range following a step change in line or load.
Voltage Balance
A power supply safety feature which shuts the device down in the
event of excess internal temperature.
In a dual, opposite polarity, power supply the difference in magnitude (in percentage) between the output voltages which are nominally equal at equal load.
Thick Film Hybrid Technology
Warm-up Drift
Thermal Protection
A method of microcircuit manufacture in which one or more
integrated circuits are combined with discrete components and
screen printed passive elements and interconnections to form
The initial change in output voltage of a power supply from turnon until it reaches thermal equilibrium.
DC/DC Terminology Rev C - 20061206
All information is believed to be accurate, but no responsibility is assumed for errors or omissions. Interpoint reserves the right to
make changes in products or specifications without notice. Copyright © 1999 - 2006 Interpoint Corporation. All rights reserved.
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