According to the three Rs—reuse, reduce and recycle—we must save our planet from e-waste. Sometimes we have a dead mobile phone whose battery is in good working condition. The circuit given here is used to utilise such batteries for making a mini candle light using bright LEDs.
The circuit is built around MC34063 DC-to-DC converter IC. It is a monolithic controller that consists of internal temperature-compensated voltage reference, comparator, controlled duty-cycle oscillator with an active current-limit circuit, driver and high-current output switch. This IC was specifically designed to step-down, step-up and for voltage-inverting applications with a minimum number of external components.
Circuit and working
Circuit diagram of the mini candle light using an old mobile phone battery is shown in Fig. 1. It is built around monolithic DC-to-DC converter controller MC34063 (IC1), 100µH inductor (L1), Schottky barrier diode 1N5819 (D1), four 5mm bright white LEDs and a few other components.
Here, IC1 is configured in step-up configuration to drive the bright white LEDs using an old mobile phone battery. The 33-ohm resistor (R4) limits the current flowing through the LEDs. Capacitor C2 determines the operating frequency of IC1, and R3 and R5 determine the output voltage.
Output voltage can be calculated by using the relationship:
When switch S1 is closed, IC1, inductor L1 and Schotky barrier diode D1 perform step-up operation and LEDs (LED1 through LED4) glow.
IC 78S40 can be used in place of MC34063. Any Schottky barrier diode works fine in this circuit. By using a low-ESR capacitor, you can increase the efficiency of the circuit.
The circuit can be converted into a small emergency light by adding a charger and a few more components.
Construction and testing
An actual-size, single-side PCB layout for the mini candle light using an old mobile phone battery is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on the PCB, enclose it in a suitable plastic box.
Download PCB and component layout: click here
The circuit works off an old mobile phone’s 3.7V battery. It will also, of course, work with any 3.7V DC power supply.
A. Samiuddhin is an electronics hobbyist. His interests include LED lightings, power electronics, microcontrollers and Arduino programming