Handy Pen Torch Circuit

Posted on Feb 5, 2014

This easy to construct Handy pen torch  electronic circuit and low component count, uses two power white LEDs for lighting. Low volt (4. 8V dc) supply available from the built in rechargeable Ni-Cd battery pack is first converted into two channel (independent) constant current sources by two pieces of the renowned precision adjustable shunt regul

Handy Pen Torch Circuit
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ator chip LM334 (IC1 and IC2). Around 25 mA at 3. 6 volt dc is available at the output of these ICs. This regulated dc supply is used to drive two power white LEDs D4 and D6. Resistors R3 and R5 limlits the output current (and hence the light output) of IC1 and IC2 circuits respectively. Diode D1 works as an input polarity guard cum reverse current flow preventer. Capacitor C1 is a simple buffer for circuit stabilization. After succesful construction, preferably on a small piece of general purpose PCB, enclose the whole circuit in a suitable and attractive pen torch cabinet. If necessary, drill suitable holes in the cabinet to attatch the dc socket, on/off switch and the input indicator etc. In prototype, commonly available 4. 8 volt/500mah Ni-Cd battery pack (for cordless telephones) is used. One very simple but reliable ac mains powered battery charger circuit for the handy pen torch is also included here. Basically the pen torch circuit is a constant current charger wired around Transistor T1 (BC636), powered by a 12v/350mA step down transformer and associated componentsD1, D2 and C1. Unregulated 12 volt dc available from the input power convereter circuit, comprising step down transformer(TRF), rectifier diodes (D1, D2) and filter capacitor (C1), is fed to T1 through a current limiting resistor R1. Grounded base PNP transistor T1 here works as a constant current generator. With 22 ohm resistor for R1, the charging...

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