SMPS designs should have clear line or patch of isolation for product safety and long term reliability. If you use opto-couplers they need to have 5kV or better isolation and 10mm between pins. The Live circuitry and the output circuitry should not overlap on PCB, tracks should not stray to the opposite side, The Transformers can be split bobbin if possible. A 10 to 20 mm desert (means no tracks) running from end to end of PCB under Transformer and under optos etc., Even ground tracks and ground planes should not stray.
The high voltage side must have layer to layer (mylar) insulation, means wind a layer and then put the yellow mylar tape, make tape concave so no strands should slip over to next layer, use split bobbin if possible. have terminations far away and enclosed for safety. vacuum impregnate with natural resin or epoxy depending on voltage and environment. product safety is very important.
If in your power supply you have a varistor, then you should have a fast acting fuse in series, as varistor fail as a short.
Wire and crimping of wires for supporting the high currents and high voltages must be carefully chosen. The copper cross section area gives its ability to carry current, the quality, thickness and flexibility of the insulation gives its voltage capability. The Tightness of the crimped contact will ensure long term reliability. Mechanical Stress prevention for all wiring is very important and guarded termination for user-operator safety.
BTA16600 and triacs of this series from ST have the metal TO220 tab electrically insulated from the device.
MOC3041 and others, switch triacs at zero crossover which reduces EMI-RFI and spikes. It means when the sine wave is close to zero volts the triac is turned on.
You have to ensure proper air circulation and fix proper heat-sinks with thermally conductive heat-sink compound or silicone grease with alumina. Anodized Aluminum heat-sinks with large surface areas and small fans are used in power electronic products for this purpose. If a component works very hot the specs will get derated, precision is lost and undesirable and unpredictable results will happen.
A thermistor must be used in series with huge power electrolytic capacitors to limit the enormous current inrush on start, or spikes may stress components, cap or EMI-RFI.
A freewheeling diode should be used across a relay, solenoid coil or motor because inductive kickback will damage transistor or mosfet. High current loads like relays can reset logic circuits if ground is not connected well, It also produces more ripple in supply, so it is better to have a separate supply for such parts.
EMI-RFI causes-Switching Loads Simultaneously (inductive loads). Power factor correction capacitors and devices. Lightning strikes (enhanced by earth faults). Line Inductance (inductive kickback, resonance). DC and AC Drives for Motors. Rectifiers with large filters and stray inductance.
Small battery operated gadgets when turned on after a very long time may not work properly due to a thin oxide layer at the battery connector, replace cells if required, scratch and clean battery and connector surface, the reason is some gadgets consume so low power that the current cannot break a micronic oxide layer. Keep using regularly.
Loose Contacts may have a resistance like 100mE (milliohm). A bit of corrosion and 10A of current will make that dissipate 100 * 102 = 10,000mW = 10W , if the contact area is 1 sqmm the heat will cause the resistance to increase, then the dissipation becomes more, sparking and welding may happen, it can even cause fire.
All Electronic Products have interfaces to external electrical circuits. The power supply is also derived using converters or power supplies. Motors, Heaters and Transformers are examples of components in the electric power circuits.
Points to bear in mind
12V lead acid batteries should be charged with a constant current CC and constant voltage charger the CV being 13.6V. Deep discharge and over charging will reduce the cycles.
Lead acid batteries need a monthly distilled water update to ensure long life, sealed lead acid dont need attention. Keep lead acid batteries in well ventilated area due to acid fumes.
Electric Shock can kill hence take great care, Electrolytic capacitors burst and Transformers catch fire. turn off equipment after use. turn off all electricity when going out of town.
Inductive kickback starts a tubelight or automobile as high voltages are produced when current in inductor is turned off. This also is the cause of failure in power semiconductors.
Earthing is important, ensure it's perfect, the neutral to earth could be 5V AC max., also a circuit breaker and fuse a must. Use a electrical earth leakage circuit breaker to protect both man and machine.
Extra care should be taken to prevent injury to eyes while working. Also 230V/110V shock can be fatal. working on high energy electrical circuits and power electronics should be with all precautions.
You need a Fuse, Circuit breaker and earth leakage circuit breaker for safety against shock and fire hazard.
High voltage or current stress, mechanical vibration, user misuse, High Energy stress (freq and voltage), aging (cycles) cause failure.
Good earthing, servo motor regulated mains supply, earth leakage circuit breaker and over current circuit breaker, HRC fuse are some safety steps to take.
When working with HV or HE circuits wear shoes, keep yourself dry, the supply board should have above protections in red.
Use silicone shrink sleeves to insulate or close exposed high voltage wire ends or joints.
Sparking at the high voltage mains supply power contacts like a plug can cause electronic gadgets to fail.
Near 2001 i started sharing my learning and experience in Electronics Engineering on Blogs and Newsletters. One of the Successful eMag and electronic email magazine ran for five years. I lost interest later in the email mag, and this magazine just morphed into a dozen or more Tech Blogs that run today. From the feedback i got, it has helped engineers and enthusiasts worldwide in Electronic Product Design.
It is called analog dial timer as it has no digital display, but the chip is digital it is CD4541. It is Mains operated, you could make on-delay or off-delay. By changing the caps and resistors or with even dip-switches you could get timing of few seconds to many hours. Circuit is Analog Timer 4541 .
Some timers energize the relay after a set delay on power start. Some start with relay energized and turn off after set time. Motors and big systems cannot take fast turn-on and turn-off, Some systems will require sections or modules to start one after another as they are interdependent.
This is in continuation of the thread called "Design of a Thermocouple Amplifier" doc00023.html which is in the same section .
This is just a formatted-edited email thread exported from Eudora from my mailbox using the content concentrator. The circuits below were made by TF a student, This thread has been put online to share information.
The part under "From: delabs" are my writing. there may be some mistakes and broken links.