Techniques of Circuit-PCB Design and Component Selection

• 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.
• All elektro-mechanical parts like switches, relays, connectors and pots have limited number of operations.
• Reinforce copper tracks on PCB with a copper wire when it needs to carry more current, tinning may improve a bit.
• Drawing a neat circuit diagram will ensure a better design, lesser parts means greater reliability, simple solutions.
• Observe color code in wires. positive is red and negative is black and green is earth and See Wire Color Code.
• High impedance points of circuit like 500 kilo ohm and above can pick up AC noise and DC leakage currents. this will affect the performance of circuit, so for DC you have to put a 'gaurd ring'of the signal ground around that point in PCB. For RF you have to shield with things related to iron and mu metal, for low signals even a copper shield will do.
• 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.
• Failure of parts are when parts are stressed beyond limit, bad environment, misuse, infant mortality and normal aging.
• 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.
• When you make a PCB try to orient all ICs in one direction, so also all diode and cap polarities, then it is easy to populate the parts, easy to verify and troubleshoot for production and testing. Read a Tutorial on PCB Design.