To modify a 12V power supply for charging a phone, first obtain a USB charging module (5V/2A) and a buck converter. Connect the 12V supply to the buck converter’s input, set the converter to output 5V, and link the USB module’s input to the converter’s output. Use a switch to control the circuit and add a diode (e.g., 1N4007) across the USB output to prevent reverse current damage. Ensure the total current draw does not exceed the power supply’s capacity. Test with a phone to verify stable charging.

The process relies on stepping down 12V to 5V using a buck converter, which efficiently reduces voltage while maintaining current capacity. USB standards (USB-IF, 2023) specify 5V nominal output with up to 2.4A for fast charging, requiring a converter with sufficient wattage (e.g., 12V/2A = 24W; 5V/2.4A = 12W). Efficiency losses typically range 80-90%, preserving ~19.2W usable power. A diode adds ~0.7V drop, ensuring safe USB voltage compliance. Data from the U.S. Department of Energy (2022) notes that 12V systems are common in automotive and industrial applications, making them adaptable for off-grid charging. However, users must prioritize components with overcurrent protection to avoid overheating or device damage. Without proper modification, a direct 12V connection can permanently harm phone batteries. This method balances simplicity and safety for emergency or DIY charging scenarios.