Download Module 8 - Control Systems: Review of Electronics Goals

Module 8 - Control Systems: Review of Electronics
Goals & Objectives
Goal: This module is to provide a review/introduction to electronics
basics. The power supply is used to discuss resistors,
capacitors, diodes, and voltage regulators. The power supply
used in the MATE ROV Control System is used as an example.
Objectives
• Upon completion of this module, the student should be able to:
• 1. Identify electronic components and describe their purpose.
• 2. Describe the differences between Linear and Switching power
supplies
• 3. Select the proper resistors required for various power supply
output voltages.
• 4. Describe the purpose of power supply filter capacitors.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Concepts
Working with electronics, we need to constantly be aware of the
four important electrical concepts of voltage, current, resistance
and power.
Each of these determines the operation of an electronic component
in a circuit. Most devices have ratings that must be followed.
Voltage – Maximum applied voltage is critical in many electronic
components. Many data sheets will specify “Absolute Maximum
Voltage”. Above that point, the manufacturer has determined
that the part will cease to function. Do not exceed this voltage
specification
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Concepts
Current – Most devices have a maximum current specification
measured in amps or milliamps. Be sure and read the device
data sheet to determine under what conditions this value is
specified. Many components have a minimum heat-sinking
requirement and are specified under a specific ambient
temperature.
Resistance – Many components have an internal resistance that
effects the operation. Batteries have and “effective” internal
resistance that limits the amount of current a battery can supply.
MOSFET transistors have an ON resistance that determines the
amount of power that is dissipated (wasted) in the device.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Concepts
Power – By paying attention to power specifications and
the power usage of your electronic component, you
can prevent devices from being overloaded and burnt
up. Resistor power specification is a common
specification that is overlooked. The formula P = I 2R
is very important in determining power dissipated in
the device.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Concepts
Power Calculation Example:
A Resistor is 150 ohms and the current through the resistor is
500 milliamps.
The power dissipated in the resistor is P = I2R (from ohms law)
P = 0.52 * 150 = 37.5 watts
This would require the selection of a resistor capable of
handling at least 37.5 watts
Use a design criteria of keeping the maximum value at 80% or
less of the component rated value
RatedValue * 80% = Maximum_Value
(37.5 W is our maximum value)
Now to select the proper resistor to use.
Rated Value = Maximum_Value / 0.8
Rated Value = 37.5 / 0.8 = 46.875 watts
This translates to a standard 50W resistor.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Concepts
Activity:
Access the Component Data Sheets to determine the Absolute
Maximum Input Voltage for the SP7805 voltage regulator.
Compare that voltage to the Recommended Operating
Conditions input voltage.
What is the percentage difference between the two values?
What are the dangers associated with using the device above
the Absolute Maximum voltage?
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
The following electronic components will be discussed
and their usage in ROV control systems covered.
Fuses and Circuit Breakers
Resistors
Capacitors
Inductors
Diodes
LEDs
Voltage Regulators
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Symbols
Standard Symbols
Resistors
Diode
Battery
Fuse Switch
Wiring
Junction
Ground
Inductor
Reference
Capacitors
LED
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Fuses & Circuit Breakers – Why Do we need them?
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Fuses?
Why are fuses important?
Watch Burning Electronics
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Fuse Symbols
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Fuses & Circuit Breakers
Fuse – A fuse is an electronic device that will limit the current in a
circuit. These are devices that self-destruct when its maximum
value is reached. This self-destruction prevents the downstream
components from being destroyed.
Typically, fuses should be selected for 125% of the maximum
current. This is another way of stating that the maximum current
should not exceed 80% of the fuse rating. All fuses have a
Time-Current curve which will show how quickly a fuse will blow
at various current levels.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Circuit Breaker and Auto-Reset Fuses – Circuit Breakers and
Auto-Reset Fuses perform the same function as fuses but are
not usually destroyed in the protection process. A circuit
breaker is a spring loaded device that when the current level
reaches a set amount, the heat generated inside the circuit
breaker, causes mechanical movement which releases the
spring tension and opens the circuit.
Auto-Reset Fuses are semiconductor devices that also heat up and
at the right level will open up. Upon cooling down and removal
of the input power, they will reset.
The selection calculations for these devices are similar to those for
fuses.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Additional Reading assignment:
Underwater Robotics, Section 7.2, Pages 421 – 425
Additional Links
http://www1.cooperbussmann.com/2/SPDTableofContents.html
http://www.cooperindustries.com/content/dam/public/bussmann/Ele
ctronics/Resources/Data%20Sheets/BUS_Elx_DS_2051_S501_
Series.pdf
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Resistor –Resistors have many purposes in electronic circuits.
They are made out of material that can provide a large amount
of resistance to current flow in a very small area. Resistors are
rated in ohms, watts and in many cases, maximum voltage.
Some uses for resistors include:
Voltage dividers to create a reference voltage.
Voltage Divider Additional Reading
Video about voltage dividers
An example of the voltage reference will be shown later in the
power supply.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
(Resistor Usages cont.)
Current monitoring – Through the use of ohms law, it you know the
resistance value and can measure the voltage across the circuit,
you can do the math to calculate the amount of current flowing
through the resistor.
For instance, if you have a 0.1 ohm resistor and measure 3.5 volts
across it, Ohms law dictates that there is 35 amps flowing
through the resistor.
I = E/R
35A = 3.5V/0.1 Ohms
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
(Resistor Usages cont.)
Level setting – many times electronics need to be held
to a certain level until the other circuitry is ready to
turn on and operate it. Resistors used in these
applications are called pull-up resistors and pull-down
resistors. They are high value resistors that will hold
an input to the required level. An example of this is
on the SeaMate Control board. Each of the MOSFET
inputs have a pull down resistor to hold the MOSFET
in the OFF state until the Arduino starts operating.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
(Resistor Usages cont.)
Current Limiting – If you were to connect a typical Light Emitting
Diode (LED) directly across 12 VDC, it would immediately burn
out. LEDs are current devices and need the amount of current
through them to be limited below it’s maximum value. Resistors
are placed in series with each LED to limit the amount of
current.
Example of a resistor with too much current flowing through it.
Additional Study:
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Capacitor – A capacitor is an energy storage device. Capacitors are
made from parallel non-touching plates.
Capacitors can almost instantaneously supply current to the circuit
until the power supply can recover and catch up.
Capacitors are utilized for
very short bursts of current
and are limited in what they
can provide. In the power
supply, capacitors are used
to filter the supply power and
provide smooth DC power
with as little voltage ripple on
it.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Capacitors are used in different values depending upon their
purpose and are rated in Farads (typically microfarads).
Power supply filter capacitors over 1000uF are common. Bypass
capacitors installed at each integrated circuit point of use are
0.01 to 0.1 uF and these are connected as close as possible to
each pin that utilizes power supply current.
For motor drivers, approximately 100uF per amp of current is
recommended to absorb the recirculating currents of the
inductive motor loads.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Capacitors (cont.)
WARNING: Capacitors have a voltage rating that must not be
exceeded.
Polarized capacitors (those with marked polarity + or -) must
never be connected with reverse polarity. Connecting a
polarized capacitor to reverse polarity (+ to – and – to +) will
cause the capacitor to explode and catch fire.
In case you missed it the first time:
Watch Burning Electronics
Additional Capacitor Information
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Inductor – Inductors are also energy storage devices. These are
typically coils of wire wound to create a specific value of
inductance. The coils shape, number of turns, and length all
determines the final inductance value. Inductors are measured
in Henries.
Inductor Video
Additional Information
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Diode – A diode is a semiconductor device that allows
the current to flow in only one direction. It is much
like a one-way gate for electrons. The plumbing
device analogy is a check valve. Diodes have a
forward voltage drop that depends upon the diode
construction. A typical voltage drop is 0.7 volts.
Diode Video
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
LED – A Light Emitting Diode (LED) is a special type of
diode that will give off light when current flows
through it. LEDs are current operated devices and
have a maximum current rating that must be adhered
to.
LEDs can be purchased in multiple colors and various
shades of white. Some LEDs have Red, Green and
Blue emitters all in the same package that allow them
to generate wide ranges of colors.
In electronic circuits small LEDs will have a small
current limiting resistor wired in series with it.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
MOSFET Transistor – A Metal Oxide Semiconductor Field Effect
Transistor (MOSFET) are typically used as electronic switches
in ROV control systems. The N-Channel MOSFET is the
simplest to control and is the most common found.
MOSFETS are three terminal devices. Two terminals are the
current in and current out pins, the third terminal is the control
pin.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
MOSFET Transistor –
An N-Channel will turn OFF if the control pin (GATE) is connected
to zero volts and turn on if the GATE is connected to 5 volts.
Microprocessor Control systems utilize MOSFETS to increase the
amount of current that the processor can turn on and off.
MOSFETS are used to in the ROV to control the speed and
direction of the thrusters.
MOSFETS are also used in the ROV to operate items such as
lights, grippers, pumps, and actuators.
MOSFET Video
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
One part of a power supply is the Voltage Regulator. It’s purpose
is to maintain the desired voltage over while the current from the
supply varies.
Keeping the voltage constant is the job of the Voltage Regulator.
Voltage regulators are rated in
Input Voltage Range
Output Current
Output Voltage
Two types of voltage regulators are used in the ROV control
system.
1.
2.
Linear Voltage Regulator
Switching Voltage Regulator
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Linear Voltage Regulators – These are typically three terminal
devices with an input pin, output pin and ground or adjust pin.
They operate on the principal of “throwing away” what the circuit
does not need and dissipating that in heat.
These are one of the simplest voltage regulators to use over a wide
range of currents.
Most linear regulators are limited in the upper range of their input
voltage.
Linear regulators are used for milliamps to up to 5 to 10 amps max.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
LM7805 Circuit
LM7805 Video
LM317 Video
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Switching Voltage Regulators – also known as Switch Mode Power
Supplies (SMPS). These regulators utilize PWM switching and
external energy storage devices (typically an inductor) to create
a wide range of output voltages.
SMPS typically have a much wider range of input voltages.
SMPS are much more efficient to use than linear regulators due to
their design.
SMPS can be electrically noisy requiring attention to be paid to
filtering their output voltages.
The SMPS in the ROV controller can handle input voltages up to
60Volts where the linear regulator is limited to 15Volts.
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Switching Voltage Regulators –
STORAGE
INDUCTOR
POWER
GOOD
LED
OUTPUT
VOLTAGE
SETTING
- VOLTAGE
DIVIDER
Regulator
Input
REVERSE
PROTECTION
DIODE
SCHOTTKY
CLAMPING
DIODE
OUTPUT
FILTER
CAPACITOR
Module 8 - Control Systems: Review of Electronics
Review of Electronics – Electronic Components
Switching Voltage Regulators –
R2
2k
R1
VOLTS
6130
5
12634
9
17512
12
24016
16
37024
24