A voltage regulator is designed to automatically maintain a constant
voltage level (Wikipedia, 2015). LM2576 voltage regulator (Fig. 2.5.0) is monolithic integrated circuit
that provides all the active functions for a step-down (buck) switching
regulator, capable of driving 3A load with excellent line and load regulation.
These devices are available in fixed output voltages of 3.3V, 5V, 12V, 15V, and
as adjustable output version. Requiring only a few external components, these
regulators are very simple to use and include internal frequency compensation
and a fixed-frequency oscillator. The LM2576 series offers a high-efficiency
replacement for popular three-terminal linear regulators. It substantially
reduces the size of the heat sink, and in some cases no heat sink is required
(Texas Instruments, 2013). A typical application of LM2576 is shown below in
Other features include a
specified ± 4% tolerance on output voltage within specified input voltages and
output load conditions, and ± 10% on the oscillator frequency. External
shutdown is included, featuring 50 ?A (typical) standby current. The output
switch includes cycle-by-cycle current limiting, as well as thermal shutdown for
full protection under fault conditions (Texas Instruments, 2013).
LM2576 IC (ti.com, 2015).
2.5.1 LM2576 Application circuit from datasheet (ti.com, 2013).
USB is currently a very popular computer interface
specification used to connect various peripheral devices to computers and
microcontrollers. Some microcontrollers provide built-in USB modules. The
18F4550, for example, has built-in USB interface capabilities.
The USB is a high-speed serial interface that can also
provide power to devices connected to it. According to the specification, the
maximum distance of a device from its host is about thirty meters, accomplished
by using five hubs. For longer-distance bus communications, other methods such
as use of Ethernet are recommended.
The USB bus specification comes in three versions:
The earlier version, USB1.1, supports 11Mbps.
USB 2.0 supports up to 480Mbps.
While the new version USB 3.0 supports the payload
throughput up to 4 Gbps.
However, this project implements USB 2.0 and therefore all
further information is related only to USB 2.0 version.
The maximum power available to an external USB device is
limited to about 100mA at 5.0V (Ibrahim, 2008).
Figure 2.6.0 shows
typical USB connectors.
Figure 2.6.0 USB connector.
USB is a four-wire interface implemented using a four-core shielded
cable. Two types of connectors are specified and used: type A and type B. The
pin-out of each type is shown below in figure 2.6.1.
Figure 2.6.1 Type A and B connector.
All four wires have specified colours. The pins and wire
colours of a Type A or Type B connector are given in table 2.6.0 below.
+ 5.0 V
Table 2.6.0 USB connector pins.
Ultiboard is a rapid
printed circuit board (PCB) prototyping environment used by engineering
professionals, educators, makers, and students across many applications. Its
seamless integration with Multisim helps circuit designers save hours of
development time with the ability to complete circuit schematics, SPICE
simulation, and PCB layout in the same environment. Ultiboard benefits include the following (National Instruments, 2015):
Flexible environment optimized for rapid design and accurate part
or copper placement.
Engineer-friendly interface for laying out and routing PCBs.
Seamless integration with Multisim to ensure accurate transfer of
Comprehensive database of connector footprints for custom designing
NI hardware and test platforms.
Easy export to industry-standard Gerber or DXF formats for
prototyping and fabrication.
Multisim is an industry-standard,
best-in-class SPICE simulation environment. It is the cornerstone of the NI
circuits teaching solution to build expertise through practical application in
designing, prototyping, and testing electrical circuits. The Multisim design
approach helps to save prototype iterations and optimize printed circuit board
(PCB) designs earlier in the process (National Instruments, 2015).