Monday, December 24, 2018

Design Notes - Power Electronics - 02

Power Supplies and SMPS, Transformers, Drive circuits for Motors, Heaters and Solenoids are all Power Electronics. Thyristors, Mosfets and High Power Transistors are important components used in these circuits.

Tek Power Supply Facia - Observe the user friendly interface design.

Tek Power supply

Power Design Points to note - delabs
  • Foldback circuits in the form of constant current or voltage can protect a Power Circuit from overload. eg. Charger.
  • Air gap in inductor core prevents saturation of the Magnetics, it must be made like that when required. eg. Choke.
  • High power equipment should have a soft start, so that fuses dont blow on start, inrush can cause damage to parts.
  • Caps can be put in series to double voltage withstand capability, when we put el-caps in series they have to be identical in value. put caps in parallel to increase the cap uF value and it also lowers ESR which is equivalent series resistance, this is good when filtering in SMPS. Two el-caps with the negatives of both connected and the positive terminals serving as the two terminals will give a non-polar cap, used in crossover networks.
  • When smps has to work at 100Khz or more, the primary of transformer must have multiple strands, and secondary can be a copper flat ribbon. this is due to skin effect, as high frequency current flows on surface of conductor.
  • MOSFET needs a turn on pulse and a turn off pulse as gate capacitance is huge.
  • Do not club Heatsinks unless the heatsink is very big or the clubbed components form a part of a current sharing set. If you club say two TO220 devices one dissipating 10W with a 2 Watt heating device, you may reduce reliability of the 2W device. Then clubbing parallel current sharing devices on one heatsink may be a good idea as it may reduce thermal runaway, also parallel power transistors should each have 0.1E in emitter path, this also can force load sharing on lazy devices.
  • Test a mosfet, charge the gate with the DMM in diode mode, then there is a short between source and drain.
  • Snubbers consisting of R-C should be used across switches, relay contacts, MOSFETS when switching inductive loads, this will absorb the spike and save the device.
  • Transformers used in SMPS could be split bobbin for product safety, and transformers should be resin impregnated, hazard may arise when using a badly made product.
  • In a SMPS which is not earthed the floating (unconnected) earth terminal will give a slight shock due to the two Y caps connected to earth from phase and neutral.
  • Power mosfets, transistors or IGBT's should be electrically isolated very well from heatsink with alumina, mica or silpad. It could withstand 2KV -5KV DC, related to product safety. Also these heatsinks should not be earthed but floating, do not fix to the metal chassis for maximum safety.
delabs design notes from the 90s

Instrumentation and Automation - 02

In Test and Measurement and Industrial Process Control a common factor is instrumentation. The measuring aspect is common to both. T&M instruments are used in Testing, Research,Automated Testing, Troubleshooting and Servicing.

Instrumentation and Automation - 02

Process control Instruments are used in Production Lines made of Machines in a Factory. It could be Counters and Timers used for Textile or Steel Industry. It can also be Temperature and Pressure Controllers used in Oil Refining or Food Processing.

So you see a difference. We have handheld Test Instruments like DMM and Scope and We have Handheld Instruments for Gas Monitoring or Humidity too. In automated testings we have rack mount test instruments. In Control panels we have Rail Mount carrying DIN standard Instruments.
  • On-Off controls or level trip relays can oscillate if hysteresis dead band is very small or absent.
  • Hysteresis is like on at 300 off at 304 like in heaters or air conditioners. If you on-off at sharp 300 there is a chatter or oscillation. This is called dead-band in temperature control. In above example 304-300=4 is the dead-band.
  • LF356, TLO71 and CA3140 are FET input Op-Amps, the bias is in pA, The caps for sample hold with these opamps are low leakage ones.10uF tantalum for long time, low resolution data. Long hold times with 12 bit data (analog) use 1uF plastic multilayer and clean-IPA + coat PCB with epoxy.
  • Design the product in such a way that neither the pot terminals or pot switch is used for mains voltage, instead use the pot switch or variable resistance for signaling and the mains can be switched with Relay or Thyristor.
  • If you need a 10.00K resistor 0.1% and you only have 1% in the market, you can trim lower values to higher values by removing the paint of the resistor and scratching the black metal film till you get the desired value. (this is only for testing or prototype development, R&D, not for manufacturing).
  • 7107 and 7135 of Intersil can be tested in-circuit, check Vref for 100mV or 1V reference, then short Vin and Vref the reading should be 1000 counts for 7107 and 10000 counts for 7135. ground plane should be good, no ground loops, PCB only glass epoxy and low leakage caps to be used, then reading will be stable, use some coating on soldered PCB.
  • An electrically Noisy environment can be simulated with a hair drier, or hot air blower. Another way Looping the NC (normally closed) contacts of a 230V Electrical Contacter-Relay can make it oscillate, this makes a lot of Sound and more important is the Electrical noise rich in EMI-RFI. This helps basic testing of timers, counters, uP, uC and embedded systems as they may malfunction in noisy environment.
  • A Single Pole 12V 100mA relay in a feedback loop, with its contacts, can make a Electrical or Electromechanical Oscillator. This can test your ground loops and digital circuit decoupling caps. It simulates power spikes which may reset some counters.
  • When a Machine with many stages or even an entire production line has to be automated, a PLC system is easiest to configure. It has digital inputs for limit switches and proximity sensors, it has analog inputs for any other parameter sensor. The PLC output modules can drive Electrical Contactor circuits with 230V Signal or 4-20 mA for an AC drive. The tacho-generator voltage feedback or pulses feedback from a motor can be fed to PLC inputs too.
  • Automation is used to enhance the quality and quantity of the product, also where there is danger to operators or workers. This moves the worker up, into the maintenance and management of materials, machines and systems.
  • Industrial Automation is essential to enhance the manufacturing worker to deliver consistent, repeatable and timely delivery of products. Absence of automation makes quality and deliveries unpredictable and stresses worker on monotonous jobs. When the worker is creatively employed with his machine on automation, it is the best scenario.

Solderman Talks 1702 AD
"Over-Automation is an utopia which is incorrect. This is because if you have no workers in any factory, there are no consumers in that city. No consumers means no sales of goods, no building of houses, no buying of automobiles. All strata of People correctly employed, reasonably paid, seeds consumerism, promotes the economy and markets. Automate everything, economy grinds to an halt."

- Solderman Talks 1702 AD

Wednesday, December 12, 2018

Theory and Tutors in Electronics

Learning electronics in theory by studying books is the conventional way, this method may help in History and Maths. Maths needs a paper and pencil for practicals and history needs a well equipped Library. In these modern times, the web has made access to wide range of learning information easy, which is true Knowledge Empowerment. The greatest gift a Child can get from the Parents or School, is Knowledge.

Electronics Theory and Tutorials  

As an Electronics Engineer i had always needed data sheets and application notes. The web makes these documents not only accessible to all, but searchable too.

Process Control Instruments

These are some instruments i manufactured when i used to run my own industrial automation business.

Theory and Tutors in Electronics

Now many Virtual Electronics Workbench Software and Interactive Tutors are available, these aid learning. We have to design, build and apply some electronic ideas in 3D Hardware, for complimenting the Book, Academic or Web learning. Practical and Theoretical study in electronics has to be in Tandem, this is possible only when Industry works with Universities to create real talent and skills in students. The applied technology is evolving, hence the academic education must be relevant when the student gets into his first job.
Solderman Talks 1702 AD
"when you solder the windows should be opened, cross ventilation must be good, because the fumes are not very good for health. After you finish wash your hands with soap, as lead is poisonous or toxic"

- Solderman Talks 1702 AD


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