AC/DC Adapters for Medical Infusion Pumps
An
AC/DC adapte
r is a type of external power supply, often enclosed in what looks like an over-sized AC wall-plug. Other
names include power adapter, power converter, plug-in adapter, adapter block, domestic mains adapter, line
power adapter, or simply AC adapter. AC adapters are used with electrical devices that require DC power but do
not have the internal circuitry to accomplish the conversion of AC to DC.
Medical-grade power supplies
are designed to meet the
IEC60601-1
medical equipment safety standard and may include typical output voltages of 3.3 to 48 Vdc, a variety of
package style (open-frame, enclosed, encapsulated, etc.), mounting options, thermal management, and
environmental features, among others.
ADC for Medical Infusion Pumps
An
Analog-to-Digital Converter
(ADC or A/D converter) measures the magnitude of an input analog signal and converts it to a digital number
that is proportional to the magnitude of the voltage or current. An
ADC
often converts real-world signals to digital signals for processing. One of the more important specifications
of an ADC is the resolution that it offers, which is the number of discrete values (represented in bits) that
the ADC produces in relation to the analog signal it is converting. The more bits, the higher the resolution.
A higher resolution yields a more accurate approximation of the analog input.
Audio Amplifiers for Medical Infusion Pumps
A
power
or
audio amplifier
is typically used to greatly increase the signal strength, or amplitude, of a current or voltage signal. In
audio applications, late stage "power" amplifiers in a signal chain can be used to increase the power output
of a signal such that the signal can physically move, or drive, the diaphragms in a loud speaker.
Audio DACs for Medical Infusion Pumps
A
digital-to-analog converter
(DAC) is a semiconductor device that is used to convert a digital code (usually binary) into an analog signal,
such as electric charge, current, or voltage. A
DAC
is the principal means by which computer and digitally-based systems translate digital data into real-world
signals. An audio-quality DAC has specifications tuned for audio applications such as a high dynamic range
with low to no distortion.
Battery Chargers for Medical Infusion Pumps
Battery charging
circuits are used to recharge batteries and are available in linear or switching topologies. They can be
completely autonomous in operation or used with a microcontroller. Generally speaking, integrated chip
charging technology can produce charge currents in a range from around 625 nA, up to around 4.5A. Battery
charger ICs often do more than just charge; they can protect from overcharging, regulate voltage, and manage
charging from irregular sources such as energy harvesters or very low voltage sources. In portable technology,
battery chargers are indispensable.
Battery Protection for Medical Infusion Pumps
Battery protection
circuits are an electronic safeguard to prevent damage to internal electronics in the event of reverse battery
installation, accidental short circuiting, or other inappropriate operation. The simplest protection for
reverse battery protection is a diode in series with the battery, however protection circuit ICs offer more
than just battery real protection and can increase the useful operating life of a rechargeable battery pack.
Buck Boost Converters for Medical Infusion Pumps
A
buck converter
is a power efficient voltage step-down converter that changes a higher voltage to a lower voltage. Whereas a
linear regulator can achieve the same purpose, regulators
can waste more energy via conversion of excess energy to heat. For this reason, a
buck DC/DC converter
is the preferred choice for power-efficient designs. A
DC/DC boost converter
, also known as a step-up converter, is a semiconductor device or electrical circuit that has an output DC
voltage that is greater than the DC input voltage. The amount of output current will be lower than the source
current, however. Boost converters can increase the voltage and thus reduce the total number of battery cells
required for portable applications.
Clocks for Medical Infusion Pumps
There are two purposes for
clocks
in electronics: to act as a hardware
timing clock
that governs the synchronization digital devices, and as a
real-time clock
(
RTC
), which keeps accurate time with respect to the end-user for record-keeping purposes. Whereas it is possible
to keep time for external users with a digital circuit timing clock, it’s not as reliable as a RTC with
battery back-up. Digital clock technology keeps electronics synchronized and is more expensive and complicated
at higher frequencies. A lower frequency clock can be used and then multiplied to achieve the desired clock
rate for digital devices; however any jitter (error) is also multiplied. (Jitter is shakiness in the signal,
caused by electro-magnetic radiation or the influence of nearby signals.) Circuitry supporting clock function
should be selected for low noise so as not to introduce error.
Current Sensing Amplifiers for Medical Infusion Pumps
Current sensing amplifiers
, also known as
current-sense
or
current-shunt amplifiers
, measure electrical current. The voltage across a resistor in a current path is directly proportional to that
current, per Ohm's law. Thus, measuring current is highly dependent upon the resistor for accuracy. Integrated
circuits for current measurement are more efficient, accurate, and are an overall lower cost solution over a
discrete current-sense solution.
DACs for Medical Infusion Pumps
A
digital-to-analog converter
(DAC) is a semiconductor device that is used to convert a digital code (usually binary) into an analog signal,
such as electric charge, current, or voltage. An
analog-to-digital converter
(ADC) performs the reverse operation. A
DAC
is the principal means by which computer and digitally-based systems translate digital data into real-world
signals.
DC/DC Controllers for Medical Infusion Pumps
DC/DC controllers
are integrated chips that offer programmable and highly adjustable power management beyond that of standard
DC/DC converters. Both are important in battery-powered devices because they can conserve power, extend
battery life, and regulate voltage. Electronic systems often have several sub-circuits, each with its own
voltage level requirement that may be higher or lower than the main power supply. Over time, battery voltage
levels decline as stored power is drained. DC/DC converter circuits can raise or lower voltage levels,
allowing a circuit to continue operation. DC/DC controllers also offer options such as multiple softstart
levels, undervoltage lockout, protection against overvoltage and undervoltage, and programmable short-circuit
protection. One advantage of DC/DC converting ICs is that a portable device can use just one battery rather
than multiple batteries to accomplish desired voltage levels.
Fuel Gauges for Medical Infusion Pumps
A
battery fuel gauge
, or
state-of-charge
(SOC) indication, has evolved from a simple warning to a more complex system level use of the information,
such as soft shutdown to prevent data loss. Considerations that affect accurate accounting for remaining
battery charge include the effects of aging, self discharge and temperature variations. The value for full
capacity is obtained and algorithms are used to calculate the remaining capacity. The drawback of this
approach is that self-discharge is difficult to model since it is a function of aging and temperature.
Interface ESD Protection for Medical Infusion Pumps
If you have ever been zapped by a socks-wearing kid who has just discovered static charge build up, you have
experienced
ESD
first hand. ESD is like a miniature, localized lightning bolt caused by an electrical discharge. ESD can have
seriously damaging effects on an integrated chip or system, or can cause poor performance or failure later on
by merely weakening the circuits.
LDOs for Medical Infusion Pumps
A
Low Drop Out
(voltage)
Regulator
maintains a constant voltage level and features a low potential at below which it can no longer reliably
regulate.
LDOs
stabilize input or supply voltages so processors and other sensitive electronics can do their jobs. LDOs are
instrumental in enabling the power-efficient portables in use today because they enable very low minimum
operating voltages.
LED Drivers for Medical Infusion Pumps
LED drivers
are a constant-current source commonly used to power LEDs for screen backlighting. LEDs are current-driven
devices whose brightness is proportional to the magnitude of forward current flow. Typical desired features
for an LED driver are direct control of current, high efficiency, PWM dimming, overvoltage protection, load
disconnect, small size, and ease of use.
Level Translators for Medical Infusion Pumps
Level translators
, or
level shifters
, are needed because voltage levels continue to migrate to lower values to support new, low-power
high-performance applications. With this change, system incompatibilities arise as technologies evolve at a
different pace. If two devices are to interface reliably, the output driver voltages must be compatible with
receiver input thresholds. For this condition to be met in mixed voltage systems, a level, or voltage
translator is often required.
Memory for Medical Infusion Pumps
"
Memory
" is a casual term used to describe a component or recording media that electronically stores data for later
use. External memory media is written to and retrieved by electronic means; in this case it is a fast but
temporary means of storage via random access memory, or
RAM
in a portable carrier that is compatible with external readers for transfer of data. Media for memory is not
always required since most processors include a small amount of storage space in their registers for data.
However, in medical devices that can log health data, external memory is critical for diagnostic and legal
purposes.
MOSFET Drivers for Medical Infusion Pumps
Designers of power electronic circuits must often drive power switches that feed DC, AC, or power signals to a
variety of loads. Logic-level electronic circuits always provide the driving signals. In general, however, the
power sources and their loads have reference levels different from that of the control circuitry (ground).
MOSFET
selection begins by choosing devices that can handle the required current, then giving careful consideration
to thermal dissipation in high current applications.
Processors for Medical Infusion Pumps
The term "
processor
" refers to an electronic device that performs computational functions and carries out the instructions of a
stored program. Other terms for processor are
microprocessor
,
central processing unit
, and
digital signal processor
. Essentially, the processor refers to "the brains of a computer."
Speakers for Medical Infusion Pumps
In any
audio application
,
speakers
are the components that take the stored electronic signals and turn them back into actual sound, supplying the
end-result of the audio system for listeners to hear. Speakers can be used for audio applications from
providing a local alarm buzzer, reproduction of original sound via playback through speakers, to sophisticated
audio applications like noise cancellation.
Temperature Sensors for Medical Infusion Pumps
A
temperature sensor
is a device that measures cold or heat as a temperature or temperature gradient. Many applications require
some implementation of temperature sensing and measurement. Often, thermal management must be performed
remotely requiring battery-powered implementations and consequently,
low power
consumption for a longer operating life.
Touch Screen Controllers for Medical Infusion Pumps
A
touch screen controller
interacts with the touch screen sensor (located between the display and a protective lens that the user
touches) to measure tiny changes in capacitance or resistance. The changes are then translated into digital
signals. The touch screen controller interfaces to the host processor to indicate finger/stylus positions,
taps, and other useful input. Some important considerations are the touch screen controller's accuracy,
environmental compensation techniques, ability to handle noise, and efficacy of algorithms.
USB for Medical Infusion Pumps
USB
is a standard connection interface between computers and digital devices. A
USB transceiver
is a physical layer device that prepares data for transmission and then sends to, and receives data from,
another transceiver. The transceiver detects connection and provides the low level USB protocol and signaling.
The term "transceiver" indicates an implementation of both the transmit and receive functions. It transmits
and receives, encodes and decodes data, provides error indication, implements buffers to stage data until it
can be managed, and adjusts for the clock rate from the serial stream on the
USB SuperSpeed
bus to match that of the "link layer" higher up on the communication stack.
USB Receptacles for Medical Infusion Pumps
USB plugs and receptacles
are meant to reduce human error by their unique shape; they fit together in only one way. USB plugs and
receptacles come in Type A (typically connecting to hosts or hubs) or Type B (typically connecting to devices)
and 3 sizes: standard, mini, and micro. Type A plugs always face upstream, Type B faces downstream.
Voltage References for Medical Infusion Pumps
A
voltage reference
produces a constant level of voltage over time regardless of load, changes in power supply or temperature.
Voltage references are used in
power supplies
,
analog-to-digital converters
,
digital-to-analog converters
, and many other applications where voltage levels must be maintained at a steady level or precision is
greatly affected or the device woudl be rendered inoperable. Voltage references can vary greatly in
performance. A voltage reference for a power supply might hold its output to within only a few per centage
points off of its nominal or stated value, however a voltage reference to instrumentation-level standards are
measured in parts per million regarding stability and precision to the nominal or specified value.
Voltage Supervisors for Medical Infusion Pumps
Supply Voltage Supervisors
monitor the primary voltage that feeds embedded electronics circuits for low voltage conditions, thus
improving system reliability. Voltage supervisors ensure a proper system power-up and power-down and work to
provide an environment for a smooth and trouble-free system. For example, a voltage supervisor can be made to
reset a controller if supply voltage conditions are too low for proper operation of the controller and keep it
in a reset mode until the unstable supply voltage conditions resolve.
Wireless for Medical Infusion Pumps
Wireless technology
enables the transfer of information over short or very long distances without cables. The term "wireless" most
often refers to telecommunications. Wireless communication is possible using a wireless transmitter and
corresponding receiver. A
wireless receiver
refers to the receiving end of the information transfer and requires less energy to operate than the active
transmitting portion where the transfer originates.
Amplifiers for Medical Infusion Pumps
Amplifiers
have enormous voltage gain, use feedback to operate, and can be classified in different ways. They can be
identified by the device they are intended to drive (e.g., headphone amplifier, speaker amplifier), the input
that they are to amplify (e.g. guitar amplifier), the frequency range of the signal (e.g., RF, Audio), and by
the function that they perform (e.g. inverting amplifier, power amplifier.)
Touch Screens for Medical Infusion Pumps
A
touchscreen
is an electronic visual display that can detect the presence and location of a touch within the display area.
A
resistive
touch screen works by applying a voltage across a resistor network and measuring the change in resistance at a
given point on the matrix where a screen is touched by an input stylus, pen, or finger. The change in the
resistance ratio marks the location on the touch screen. With most
capacitive
touchscreen panels, touching the surface of the screen changes the screen's electrostatic field, which is
measured as a change in capacitance. There are different technologies to determine the location of the touch;
but in any case the location is then sent to the controller for processing. Unlike a resistive touchscreen,
most capacitive touchscreens cannot be used with electrically insulating material, such as gloves.
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