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Two-Cell LED Torch Schematic Circuit Diagram

Affordable LED Torch Revival

Often, the need to replace batteries in an LED torch can be surprising, especially when realizing they’re costly lithium cells instead of the usual inexpensive alkaline ones. While the torch might have been a freebie from a promotional event, discovering that a replacement battery costs more than the torch’s value can be disheartening. Instead of discarding the torch, consider this circuit. It employs a traditional two-transistor astable multivibrator setup, driving the LEDs via a transformer powered by two standard 1.5 V alkaline batteries. The multivibrator’s operational principle is well-documented. Producing a square wave output at approximately 800 Hz with the specified components. This signal then energizes a small transformer, delivering its output to two LEDs connected in series.

Economical Power Solution

This circuit offers a cost-effective alternative by utilizing readily available and affordable alkaline batteries, making the torch’s operation financially viable. The astable multivibrator’s steady oscillation, managed by the chosen components, ensures a consistent and reliable power supply to the LEDs. By repurposing the torch with this circuit, you can extend its lifespan without the burden of exorbitant battery costs. Making it both environmentally friendly and budget-conscious.

Two-Cell LED Torch Schematic Circuit Diagram

Flexible Transformer Choice

In the original design, Conrad Electronics provided the transformer, featuring windings with a 1:5 ratio. Although the specified transformer is available under part number 516236 on the company’s German website (, using an identical model is not mandatory. Any similar transformer with matching specifications will suffice for the circuit’s operation. Ensuring the correct installation of the transformer is crucial; an ohmmeter can be utilized to confirm the resistance of the primary and secondary windings if there’s uncertainty about their identification.

LED Configuration and Angling

The LEDs in this circuit are driven by alternating voltage and conduct during the half-wave when forward biased. Experimentation is encouraged: Reversing both LEDs can be attempted to assess if they illuminate more brightly. Notably, the design doesn’t necessitate a resistor in series with the LEDs due to the impedance of the transformer’s secondary winding. These white LEDs come with a built-in reflector, eliminating the need for an external reflector or lens glass. Mounting options are versatile; the LEDs can be positioned to focus on a single spot or angled to provide a broader area of illumination, catering to specific requirements.

Power Source Versatility

The circuit exhibits low current consumption, approximately 50 mA, making it energy-efficient. Remarkably, even when the battery voltage drops to 1 V. The design can still produce a useful light output. For power, two AAA or AA size alkaline cells connected in series are suitable. Alternatively, the circuit can be powered by two rechargeable NiMH cells. Offering users flexibility in their choice of power source. This adaptability enhances the circuit’s applicability and user convenience.


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