Digital equipment such as computers, telecommunication systems and instruments use microprocessors that
operate at high frequencies allowing them to carry out millions or even billions of operations per second. A
disturbance in the electrical supply lasting just a few milliseconds can affect thousands or millions of basic
operations. The result may be malfunctioning and loss of data with dangerous or costly consequences (e.g.
loss of production). That is why many loads, called sensitive or critical loads, require a supply that is
protected. Many manufacturers of sensitive equipment specify very strict tolerances, much stricter than
those in the distribution system for the supply of their equipment, one example being Computer Business
Equipment Manufacturer’s Association for computer equipment against distribution system disturbances.
The design of this uninterrupted power supply (UPS) for personal computer (PC) is necessitated due to a
need for enhanced portability in the design of personal computer desktop workstations. Apart from its
original functionality as a backup source of power, this design incorporates the unit within the system unit
casing, thereby reducing the number of system components available. Also, the embedding of this unit
removes the untidiness of connecting wires and makes the whole computer act like a laptop. Not to be left
out is the choice of a microcontroller as an important part of the circuitry. This has eliminated the weight
and space-consuming components that make up an original design. The singular use of this microcontroller
places the UPS under the class of an advanced technology device.
Embedded System, Uninterrupted Power Supply, Personal Computer, Automation, Power Electronics.
An uninterruptible power supply, commonly called a UPS is a device that has the ability to
convert and control direct current (DC) energy to alternating current (AC) energy. It uses a
conventional battery of 12V rating as the input source and by the action of the inverter circuitry, it
produces an alternating voltage which is sent to the load. This particular UPS is designed for a
small scale load like a personal computer and hence only a basic power rate is generated by the
UPS. Many believe that because an inverter is operating from a nominal 12V battery and it cannot
deliver as much output as a normal mains power outlet, it’s relatively safe. This is not usually
true. Even a low power inverter rated at a mere 60watts has an output which is potentially fatal if 2
you become its load. Such an inverter can have a typical output of 350mA at 230V. This is above
ten (10) times the current level connected to cause fatal fibrillation and stop your heart.
Generally, uninterrupted power supply (UPS) can be grouped by source or method of
functionality. (1) By Source: Here we have a voltage source (DC) for its operation or a current
source (DC). The current source however is used for very high power consumption devices hence
this design is a voltage source UPS. (2) By Functionality: Amongst others here is the single-
tracked and dual-tract UPS. The single-tract UPS feeds the load continuously from the rectified
DC supply directly. This type of UPS is disadvantaged because a fault in the rectification stage
leads to a complete system failure. The dual tract acts like the single tract but it has a bypass that
sources from the mains supply. Hence the battery is used only as backup and does not run all the
time unlike the single track. This design is a dual track methodology. For an ideal UPS, basic
functionality is needed (1) Being a backup utility, a UPS must ensure that there is no break in the
power supply at any point in time unless major faults like fuse cuts are experienced. (2) An ideal
UPS must provide the battery with an adequate charge so as to maintain the optimum conversion
rate to AC when needed. (3) It must also ensure overcharge protection to prevent the battery from
being damaged. (4) All forms of surges and undesired waveforms that may emanate from inverted
source voltage are to be filtered and well suited to the output level. (5) Must be sensitive to
maintain stability when the battery safe voltage is being exceeded. (6) It must also provide an
overload protection for the entire unit.
Many embedded devices provide a rich GUI-based user experience; use file systems,
multiprocessing, and multi-threading; and include networking. An operating system (OS) can
provide these features to support the rapid development of application programs [1, 2]. In
charging a battery of the personal computer (PC), a cheap, unattended, unregulated charger can
destroy a battery by overcharging it. A temperature compensated charger is also highly
recommended . Thus most power supplies have a PWM controller based on the well-known
TL494  or equivalent chips (for instance KA7500). TL494 features two error amplifiers, but
most power supplies only use one of these. A PWM controller featuring two error amplifiers is
recommended in some design because one controls the output voltage and the other controls the
However, after careful consideration of any existing design of the UPS and some embedded
systems, this particular design incorporated the following methodology upgrades: (1) The battery
charging unit is basically handled by the micro-controller which detects in split microseconds the
point at which the safe battery (voltage at which operating the battery to generate alternating
voltage is not safe) is being exceeded. This causes the system to shut down in order to prevent
damage to the battery. (2) Also handled by the microcontroller is the overcharge protection. The
controller disengages the battery at full charge voltage. (3) Application software interfaced via the
USB (Universal Serial Bus) port of the computer motherboard maintains a constant check link
between the operating system and the UPS. (4) To enhance compactness, 2-pole relays and
switches are used to eliminate duplication of components. (5) Very simple and readily available
components are sourced making the device commercially viable.
For clarity and neatness of presentation, the article is outlined into five (5) sections. The First
Section gives a general introduction of a UPS and smart embedded systems. Review of system
components used for this system design is presented in Section Two. In Section Three, we outline
the design and implementation procedures. Section Four presents the experimental results and
discussion of the results. In Section Five, we conclude the work with some recommendations.
Finally, the references are presented at the end of the paper.