delabs Circuits

Sunday, January 18, 2009

Design Notes - Components Selection - 05

Selecting the parts for your product design, choosing the components intelligently is a part of Product Design Engineering.

Budget, Availability, Size, Alternate Vendors, Product Life and Quantity to be manufactured are some factors that determine the selection of a prudent and experienced design professional.

To choose the right type of part, an exhuastive knowledge of the behaviour of passives and discretes is essential. Some points i remember among the things that i learnt the hard way are listed below.
  • Over rate components at least double, if you need a 1A-100V-100uS diode, use a 2A-200V-50uS diode.
  • Electrolytic capacitors have a shelf life, if you need to store them you have to charge them every month.
  • Gold plating is used in connectors because it has low contact resistance and does not corrode or react
  • Use a 100uF and 0.1uF CD in parallel to filter because the inductance of 100uF is a lot (the electrodes are wound as in a coil) and high frequency passes over and is filtered by the 0.1uF which has negligible inductance.
  • Ceramic capacitors leak a bit, electrolytics leak a lot but plastic or mica capacitors do not leak at all, near perfect. An oscillator with a RC time setting needs a plastic cap for stability.
  • In industrial electronics equipment, connectors are a source of many problems, hence avoid connectors. vibrations, corrosion and frequent usage will result in strange problems.
  • Small signal diode 1N4148 switches at 4nS, current of 70mA and 70V withstand capacity.
  • 2N2222 and 2N2907 form a fast switching NPN-PNP pair and have been around for decades.
  • LED displays are best indoors and are not so good for sunlit outdoors, LCD is good for that.
  • All electromechanical parts like switches, relays, connectors and pots have limited number of operations.
  • Failure of parts are when parts are stressed beyond limit, bad environment, misuse, infant mortality and normal aging.
  • Most pots have a dielectric insulation between metal pot shaft and terminals of 1KV or more. Some commercial pots may have lesser breakdown voltage and that will be a product safety issue. So either way use Plastic Knobs or pots with plastic shafts.

Contents

Basic Electronics
Basics of Electronics
Product Production
Work Discipline
Testing Points
Learning Electronics
Electronics Theory

Production Notes
Prototype Fabrication
Electrical Circuits
Electromechanical


Library
Scots Guide Electronics
Engineering - Wikibooks
Design Lab - Jim Svoboda
DC Circuits UOG
Socratic Electronics
Blobz Guide Electric Circuits


Product Design
Product Development
Constant Current Source
Good Voltage Regulators
Insulation Resistance
Digital Insulation Tester
DN Schematic PCB 04
DN Product Design 07


Hobby Circuits
VU Meter Circuits
LED brightness control
555 Incredible Chip
Process Control
liquid level measurement
Thermocouples and RTD
Design ADC Interface uC
Thermocouple Amplifier
IA Instrumentation 02
Temperature on DMM
Optical Proximity Switch
Analog Mux - Data Acquisition


Test Measurement
Instrumentation Automation
NI Test and Measurement
DMM Digital Multi Meter
Oscilloscope in T&M
IA Automation 01
Build Instruments
Tektronix T&M Equipment
Educators Corner – Agilent


Power Electronics
UPS Background
Transformer Connections
DN Power Electronics 03
DN Power Electronics 02
Half Bridge Convertor SG3525


Embedded
Interfacing Microcontrollers
Embedded Process Control
80C31 8052 Microcontroller
Microprocessors and uC
Embedded Systems Design

Components
Good Voltage Regulators
Relays and Contactors
Potentiometers Trimpots
Prototype Boards Types
Types of Capacitors
Types of Switches
Resistors How they Work
Coils Transformers SMPS
Mains Transformers Types
DN Components Selection 05

Tutor Gadgets
Count-Up Timer
Digital Logic Gates
Electronics Tutors

History
Teaching Instruments
Charles Proteus Steinmetz
Muntzing a Circuit Design
Teralab Electronics projects
Historical Instruments


Tables, Charts, Videos
Binary and Hex
Resistor Color Code
Ohms Law
Giga, Tera, Pico, Nano
High Resistance Materials

Analog
School - Analog Design
DN Analog Basics 06
DN Op-Amps 01
TI Semiconductors