Here is a rechargeable LEDlamp that gives you brightlight for a long duration oftime as it consumes little power. Thecircuit presented here is compact, automatic,reliable, low-cost and easy toassemble.The circuit comprises power supply,battery charging and switching sections. The power supply sectiontakes power from 230V AC mainssupply without using a transformer.Capacitor C1 is used as an AC voltagedropper—a well-known transformerlesssolution. This helps to make thecircuit compact without generatingheat, as capacitor C1 dissipates negligiblepower. Capacitor C1 also protectsagainst fluctuations in mains.Current required for the batterycharging circuit is provided by ca pacitor C1. Capacitor C1 dischargesthrough resistor R1 when the circuit isdisconnected from the mains voltage.This helps to prevent a fatal shock dueto any voltage remaining in the inputterminals. Capacitor C1 must be ratedat least 440V AC, with mains applicationclass X2.The AC mains voltage after capacitorC1 is given to bridge rectifierdiodes D1 through D4 to convert alternatingcurrent into direct currentand filtered by capacitor C2. The voltagefrom point B+ is given to positiveterminal of the battery (BATT), anodesof LEDs (LED2 through LED21) andtransistor base-bias resistor R3 throughslide switch S1. The circuit is operatedin three modes (AC/charge, off andbatt) by using three-position switch S1.When switch S1 is in middle position,the circuit is off. When S1 istowards right, white LEDs glow bydrawing power from 4V battery. WhenS1 is towards left, the circuit connectsto AC mains and battery starts charging.The presence of AC mains voltageand battery charging is indicated byLED1. White LEDs remain off if ACmains supply is available and glow inthe absence of AC mains.When switch S1 is towardsleft position and AC mains isavailable, the battery chargesthrough diode D6 and the whiteLEDs don’t glow. The negativeDC path through diode D5makes the transistor cut-off, preventingthe battery current fromLEDs to the negative terminalthrough the transistor. Thus thewhite LEDs don’t glow.On the other hand, if ACmains is not available, chargingstops and the base of transistorSS8050 gets positive voltagefrom the battery through slideswitch S1 and resistor R3. Thetransistor conducts and the currentflows from the battery’s positiveterminal to the negative terminalof the battery through theLEDs (LED2 through LED21),collector to emitter of transistorT1 and switch S1. Thus the whiteLEDs glow.When the switch is in ‘batt’ position,the white LEDs (LED2 throughLED21) get the supply directly from 4Vbattery through switch S1 and thereforeall the white LEDs glow.Assemble the circuit on a generalpurposePCB and enclose in a suitablecabinet. Fix the mains power cord onthe back of the cabinet and slide switchand LEDs on the front side

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