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Power Electronics

• Power Electronic Circuits.
  
• Power Supplies Section.
  
• Solid State Relays - SSR.
  
• High Energy Circuits.
• Mains Voltage Current LED Indicators
• Simple Mains Voltage monitor LM324
• Mains Voltage monitor using LM3914

Power Electronics and Energy Management

Power Electronics

Here are power supply, inverter, drives, chargers and high current equipment diagrams and links. There are Mosfet and Thyristor  circuits too.

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Power Supplies, Inverters, UPS, Chargers, Electro Plating, Precision Welding-erosion, Coating Metals and many other Processes are made of high current circuits.  Even in measurement of parameters like Micro-Ohm high currents are involved.  Electronic Circuits are required in such products to give control to time, current, frequency and voltage in order to accomplish with the required precision a process or job.

Solid State Relays or Thyristor Contacters

In any power equipment, efficiency and reduction of bulk is crucial so SMPS and high frequency control is an important part of this domain. These products also generate EMI-RFI. Product Safety Study  is also vital.

EMI RFI Filters and Electrical Noise Control

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Design Notes

(These are notes jotted down of my experience in the 90s, it may have spelling and other errors)

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.

Related Pages in delabs

• High Resistance Insulation Materials
• Mains Voltage Power Transformers
• Stabilizer Step up 230V AC 500VA
• Solid-State Stabilizer Step up 110V AC

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.

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.

Design Notes - Power Electronics - 02

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Mains Stability and Supply Regulation - Power Electronics Design Methods

• 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.