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Fitting switches which turn off automatically after a preset time in these locations can reduce the electricity consumed quite significantly. A single 100W bulb left burning all night (say eight hours) would consume 800W/hrs. The same bulb fitted with a switch which turned off automatically after say five minutes would consume only 83W/hrs, even in the unlikely event that it were to be activated ten times during this period. Triac Control There are two major problems to solve when designing a touch switch to replace a conventional mechanical light switch and these concern the power supply and noise immunity. The main switching element used to control the light is a triac, a semiconductor a.c. switch. This is normally in its off or non-conducting state but can be switched into conduction by means of a small trigger current fed to its gate terminal. Once triggered it will remain conducting until the current through it drops below a certain value (known as the holding current). This occur...

The power line fluctuations and cut-offs cause damages to electrical appliances connected to the line. It is more serious in the case of domestic appliances like fridge and air conditioners. If a fridge is operated on low voltage, excessive current flows through the motor, which heats up, and get damaged. The under/over voltage protection circuit with time delay presented here is a low cost and reliable circuit for protecting such equipments from damages. Whenever the power line is switched on it gets connected to the appliance only after a delay of a fixed time. If there is hi/low fluctuations beyond sets limits the appliance get disconnected. The system tries to connect the power back after the specific time delay, the delay being counted from the time of disconnection. If the power down time (time for which the voltage is beyond limits) is less than the delay time, the power resumes after the delay: If it is equal or more, then the power resumes directly. This circuit has been desig...

Understanding the parameters of "diode recovery time" .For prospective technicians are still learning and inexperienced, they generally recognize only two kinds of parameters of a diode, namely: The maximum working voltage (bias voltage when he gets back - or when not deliver - or when "off") The maximum operating current (when he gets a forward bias voltage of - or as leads - or when "on") Fast  Recovery diodes A similar experience we had some twenty years ago when a new SMPS first introduced on the television. When there is a diode voltage B + is broken. And then we replace the diode from the outside (our point of diode being sold in stores, rather than the official service) diode turns hot and soon broken. We think that the replacement diode voltage or current is less bulky. Then after replacement with a larger, but the result remains the same damage. Finally we order the diode with the same part number, and when the part arrived and was installed wrong...