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

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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.

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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 the device.

2 R is very important in determining power dissipated in

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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 = I 2 R (from ohms law) P = 0.5

2 * 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 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

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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.

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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.

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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

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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

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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. Linear Voltage Regulator 2. 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 R1

6130 12634 17512 24016 37024 2k

VOLTS

5 9 12 16 24