What is Zener Diode?

Zener diode

       

    

Zener diodes are a special kind of diode which permits current to flow in the forward direction. What makes them different from other diodes is that Zener diodes will also allow current to flow in the reverse direction when the voltage is above a certain value. This breakdown voltage is known as the Zener voltage. In a standard diode, the Zener voltage is high, and the diode is permanently damaged if a reverse current above that value is allowed to pass through it. Zener diodes are designed in a way where the Zener voltage is a much lower value. There is a controlled breakdown which does not damage the diode when a reverse current above the Zener voltage passes through a Zener diode.

Types of Zener Diodes

There are many different kinds of Zener diodes. At Future Electronics we stock many of the most common types categorized by power dissipation, nominal working voltage, forward (drive) current, forward voltage, packaging type and maximum reverse current. The parametric filters on our website can help refine your search results depending on the required specifications.

The most common values for nominal working voltage are 5.1 V, 5.6 V, 6.2 V, 12 V and 15 V. We also carry Zener diodes with nominal working voltage up to 1 kV. Forward (drive) current can have a range from 200 uA to 200 A, with the most common forward (drive) current being 10 mA or 200 mA.

Zener Diodes from Future Electronics

Future Electronics has a full Zener diode chip selection from several manufacturers when designing a circuit and looking for a Zener diode regulator, low voltage Zener diode, high voltage Zener diode, power Zener diode, Zener diode rectifier, 3v Zener diode, 5v Zener diode, 12v Zener diode, 18v Zener diode, 24v Zener diode or for any Zener diode circuits. Simply choose from the Zener diode technical attributes below and your search results will quickly be narrowed in order to match your specific Zener diode application needs.

If you have a preferred brand, we deal with several semiconductor manufacturers such as Fairchild, NXP, Diodes Inc., ON Semiconductor or Vishay, among other chip manufacturers. You can easily refine your Zener diode product search results by clicking your preferred Zener diode brand below from our list of manufacturers.

Applications for Zener Diodes:

Zener diodes can be found in several applications. Some of these are: voltage stabilizers or regulators (in shunt mode), surge suppressors for device protection, peak clippers, switching operations, reference elements and in meter protection applications. The constant reverse voltage of a Zener diode renders it a very useful component in regulating the output voltage against variations in the load resistance or variations in the input voltage from an unregulated power supply. The current through the Zener diode will change in order to keep the voltage within the threshold limits of Zener action and the maximum power that it can dissipate.

Choosing the Right Zener Diode:

When you are looking for the right Zener diodes, with the FutureElectronics.com parametric search, you can filter the results by various attributes: by Forward (Drive) Current (200 uA, 10 mA, 200 mA, 250 mA, 1A,…), Forward Voltage (700 mV, 900 mV, 1.1 V, 1.2 V, 1.5V,…) and Power Dissipation (from 100 mW to 1.5 kW) to name a few. You will be able to find the right semiconductor chip when designing a circuit that requires a Zener diode regulator, power Zener diode, 5v Zener diode, 12v Zener diode, 18v Zener diode, 24v Zener diode, high voltage Zener diode, low voltage Zener diode, Zener diode rectifier, 3v Zener diode or for designing any Zener diode circuits.

Zener Diodes in Production Ready Packaging or R&D Quantities

If the quantity of Zener diodes that you require is less than a full reel, we offer customers many of our Zener diode products in tube, tray or individual quantities that will help you avoid unneeded surplus.

In addition, Future Electronics offers clients a unique bonded inventory program that is designed to eliminate potential problems that could arise from an unpredictable supply of products containing raw metals and products with long or erratic lead times. Talk with your nearest Future Electronics branch and find out more on how you and your company can avoid possible shortages.

What is Diode ?

Diode

          

         

A p–n junction is a boundary or interface between two types of semiconductor material, p-type and n-type, inside a single crystal of semiconductor. It is created by doping, for example by ion implantation, diffusion ofdopants, or by epitaxy (growing a layer of crystal doped with one type of dopant on top of a layer of crystal doped with another type of dopant). If two separate pieces of material were used, this would introduce a grain boundary between the semiconductors that would severely inhibit its utility by scattering the electrons andholes

p–n junctions are elementary "building blocks" of most semiconductor electronic devices such as diodes,transistors, solar cells, LEDs, and integrated circuits; they are the active sites where the electronic action of the device takes place. For example, a common type of transistor, the bipolar junction transistor, consists of two p–n junctions in series, in the form n–p–n or p–n–p.

The discovery of the p–n junction is usually attributed to American physicist Russell Ohl of Bell Laboratories.^[1] However, Vadim Lashkaryov reported discovery of p-n-junctions in CuO and silver sulphide photocells and selenium rectifiers in 1941.

DIODE

A diode is a specialized electronic component with two electrodes called the anode and thecathode. Most diodes are made with semiconductor materials such as silicon, germanium, or selenium. Some diodes are comprised of metal electrodes in a chamber evacuated or filled with a pure elemental gas at low pressure. Diodes can be used as rectifiers, signal limiters, voltage regulators, switches, signal modulators, signal mixers, signal demodulators, and oscillators.

The fundamental property of a diode is its tendency to conduct electric current in only one direction. When the cathode is negatively charged relative to the anode at a voltage greater than a certain minimum called forward breakover, then current flows through the diode. If the cathode is positive with respect to the anode, is at the same voltage as the anode, or is negative by an amount less than the forward breakover voltage, then the diode does not conduct current. This is a simplistic view, but is true for diodes operating as rectifiers, switches, and limiters. The forward breakover voltage is approximately six tenths of a volt (0.6 V) for silicon devices, 0.3 V for germanium devices, and 1 V for selenium devices.

The above general rule notwithstanding, if the cathode voltage is positive relative to the anode voltage by a great enough amount, the diode will conduct current. The voltage required to produce this phenomenon, known as the avalanche voltage, varies greatly depending on the nature of the semiconductor material from which the device is fabricated. The avalanche voltage can range from a few volts up to several hundred volts.

When an analog signal passes through a diode operating at or near its forward breakover point, the signal waveform is distorted. This nonlinearity allows for modulation, demodulation, and signal mixing. In addition, signals are generated at harmonics, or integral multiples of the input frequency. Some diodes also have a characteristic that is imprecisely termed negative resistance. Diodes of this type, with the application of a voltage at the correct level and the polarity, generate analog signals at microwave radio frequencies.

Semiconductor diodes can be designed to produce direct current (DC) when visible light,infrared transmission (IR), or ultraviolet (UV) energy strikes them. These diodes are known as photovoltaic cells and are the basis for solar electric energy systems and photosensors. Yet another form of diode, commonly used in electronic and computer equipment, emits visible light or IR energy when current passes through it. Such a device is the familiar light-emitting diode (LED).

FORWARD BIAS DIODE

This forward-bias voltage drop exhibited by the diode is due to the action of the depletion region formed by the P-N junction under the influence of an applied voltage. If no voltage applied is across a semiconductor diode, a thin depletion region exists around the region of the P-N junction, preventing current flow.

REVERSE BIAS DIODE

Connecting the p-type region to the negative terminal of the battery and the n-type region to the positive terminal corresponds to reverse bias. If a diode is reverse-biased, the voltageat the cathode is comparatively higher than the anode. Therefore, no current will flow until the diode breaks down.

What Is A Programmable Logic Controller (PLC)?

Programmable logic controller

A PROGRAMMABLE LOGIC CONTROLLER (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices.

Almost any production line, machine function, or process can be greatly enhanced using this type of control system. However, the biggest benefit in using a PLC is the ability to change and replicate the operation or process while collecting and communicating vital information.

Another advantage of a PLC system is that it is modular. That is, you can mix and match the types of Input and Output devices to best suit your application.

 History of PLCs

The first Programmable Logic Controllers were designed and developed by Mod-icon as a relay re-placer for GM and Land-is.

• These controllers eliminated the need for rewiring and adding additional hardware for each new configuration of logic.
• The new system drastically increased the functionality of the controls while reducing the cabinet space that housed the logic.
• The first PLC, model 084, was invented by Dick Morley in 1969
• The first commercial successful PLC, the 184, was introduced in 1973 and was designed by Michael Green-berg. 

 What Is Inside A PLC?

The Central Processing Unit, the CPU, contains an internal program that tells the PLC how to perform the following functions:

• Execute the Control Instructions contained in the User's Programs. This program is stored in "nonvolatile" memory, meaning that the program will not be lost if power is removed
• Communicate with other devices, which can include I/O Devices, Programming Devices, Networks, and even other PLCs.
• Perform Housekeeping activities such as Communications, Internal Diagnostics, etc.

 How Does A PLC Operate?

There are four basic steps in the operation of all PLCs; Input Scan, Program Scan, Output Scan, and Housekeeping. These steps continually take place in a repeating loop.

Four Steps In The PLC Operations 1.) Input Scan Detects the state of all input devices that are connected to the PLC 2.) Program Scan Executes the user created program logic 3.) Output Scan Energizes or de-energize all output devices that are connected to the PLC. 4.) Housekeeping This step includes communications with programming terminals, internal diagnostics, etc...

These steps are continually processed in a loop.

 What Programming Language Is Used To Program A PLC?

While Ladder Logic is the most commonly used PLC programming language, it is not the only one. The following table lists of some of languages that are used to program a PLC.

Ladder Diagram (LD) Traditional ladder logic is graphical programming language. Initially programmed with simple contacts that simulated the opening and closing of relays, Ladder Logic programming has been expanded to include such functions as counters, timers, shift registers, and math operations.

Function Block Diagram (FBD) - A graphical language for depicting signal and data flows through re-usable function blocks. FBD is very useful for expressing the interconnection of control system algorithms and logic.

Structured Text (ST) – A high level text language that encourages structured programming. It has a language structure (syntax) that strongly resembles PASCAL and supports a wide range of standard functions and operators. For example; If Speed1 > 100.0 then     Flow_Rate: = 50.0 + Offset_A1; Else     Flow_Rate: = 100.0; Steam: = ON End_If;

Instruction List (IL): A low level “assembler like” language that is based on similar instructions list languages found in a wide range of today’s PLCs. LD MPC LD ST RESET: ST   R1 RESET PRESS_1 MAX_PRESS LD    0 A_X43

Sequential Function Chart (SFC) A method of programming complex control systems at a more highly structured level. A SFC program is an overview of the control system, in which the basic building blocks are entire program files. Each program file is created using one of the other types of programming languages. The SFC approach coordinates large, complicated programming tasks into smaller, more manageable tasks.

 What Are Input/Output Devices?

INPUTS		OUTPUTS
– Switches and Pushbuttons – Sensing Devices   • Limit Switches • Photoelectric Sensors • Proximity Sensors		– Valves – Motor Starters – Solenoids – Acuators
– Conditon Sensors – Encoders   • Pressure Switches • Level Switches • Temperature Switches • Vacuum Switches • Float Switches		– Horns and Alarms – Stack lights – Control Relays – Counter/Totalizer  – Pumps  – Printers – Fans

 What Do I Need To Consider When Choosing A PLC?

There are many PLC systems on the market today. Other than cost, you must consider the following when deciding which one will best suit the needs of your application.

• Will the system be powered by AC or DC voltage?
• Does the PLC have enough memory to run my user program?
• Does the system run fast enough to meet my application’s requirements?
• What type of software is used to program the PLC?
• Will the PLC be able to manage the number of inputs and outputs that my application requires?
• If required by your application, can the PLC handle analog inputs and outputs, or maybe a combination of both analog and discrete inputs and outputs?
• How am I going to communicate with my PLC?
• Do I need network connectivity and can it be added to my PLC?
• Will the system be located in one place or spread out over a large area?

 PLC Acronyms

The following table shows a list of commonly used Acronyms that you see when researching or using your PLC.

ASCII	American Standard Code for Information Interchange
BCD	Binary Coded Decimal
CSA	Canadian Standards Association
DIO	Distributed I/O
EIA	Electronic Industries Association
EMI	ElectroMagnetic Interference
HMI	Human Machine Interface
IEC	International Electrotechnical Commission
IEEE	Institute of Electrical and Electronic Engineers
I/O	Input(s) and/or Output(s)
ISO	International Standards Organization
LL	Ladder Logic
LSB	Least Significant Bit
MMI	Man Machine Interface
MODICON	MOdular DIgital CONtoller
MSB	Most Significant Bit
PID	Proportional Integral Derivative (feedback control)
RF	Radio Frequency
RIO	Remote I/O
RTU	Remote Terminal Unit
SCADA	Supervisory Control And Data Acquisition
TCP/IP	Transmission Control Protocol / Internet Protocol

portions of this tutorial contributed by www.modicon.com and www.searcheng.co.uk

A small number of U.S. based tech companies design, manufacture and sell PLC modules. Advanced Micro Controls Inc (AMCI) is such a company, specializing in Position Sensing interfaces and Motion Control modules.

The company's products are listed below for your reference:

AMCI PLC Modules Index: Allen-Bradley | GE Fanuc | Schneider (please scroll to view)
Allen-Bradley:
ControlLogix PLC	CompactLogixPLC	MicroLogix 1500 PLC	POINT I/O
Analog Inspection    Resolver Interface    SSI Interface    PLS Control    Stepper Control	Resolver Interface    PLS Control    SSI Interface    Stepper Control	Resolver Interface    PLS Control    SSI Interface    Stepper Control	Stepper Control
SLC500 PLC	PLC-5 PLC
Resolver Interface    LDT/SSI Interface    PLS Control    EasyPack Series    PressPRO Series	Resolver Interface    LDT/SSI Interface    PLS Control    EasyPack Series    PressPRO Series
GE Fanuc:
GE Fanuc 90-30 Series PLC	GE Fanuc 90-70 Series PLC
Resolver Interface    SSI/LDT Interface	Resolver Interface    SSI/LDT Interface    PLS Controllers
Schneider Automation:
Modicon Quantum PLC	Square D SY/MAX PLC
Resolver Interface	Resolver Interface

Electronic Testing Design, Electronic Production Technologies, Solar Systems , Technical Management, Management Proficiency, Electronics Troubleshooting, Basic Safety, Quality Focus, Process Improvement , Leadership. Solar Systems design & installation would be an asset.
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