SCR Latching Circuit. Design Note 21

SCR Silicon Controlled Rectifier ( SCR) is a semiconductor device used in switching applications. Unlike Transistors, SCR latches once triggered and remain on even if the triggering voltage at the gate is removed. The device can be switched off by removing the Anode current through a Push- to- off switch or by disconnecting the power supply.
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Make a Joule Thief. Design Note 20

Joul-Thief-CircuitJoule thief circuit is a self oscillating voltage booster circuit that gives high volt from low volt, say 3 volt from 1.5 volt. So by exploiting this property, we can light a 3 volt LED using 1.5 volt pen cell or charge a mobile phone from 3 volt solar cell or two 3 volt pen cells. It is called as “Joule thief” because it is stealing energy or joules from the battery. Let us design the Joule thief circuit.

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Infrared Alarm System. Design Note. 19

IR-LED-PairThis design note explains how to design an invisible alarm system easily. Infrared Transmitter ( Tx) and Receiver ( Rx) LED pair is easily available which can be used for making this alarm system. Infrared transmitter LED emits infrared rays in the wavelength around 950 nm. This LED is a high current device that can handle more than 100 mA current. The IR receiver LED is a kind of Photodiode that generates a Photo current when it receives IR rays. So the IR LED pair is ideal to make an alarm system that operates both day and night.
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