Key benefits Provides a simple, reliable way to apply a controlled electronic load to USB 5 V sources for testing and discharge. Lets you pick between fixed resistance values or a lower combined resistance by switching resistors in parallel, so you can simulate different load conditions without extra hardware. Clear, physics-based behavior: resistance values and resulting currents follow standard Ohm’s law and parallel-resistance formulas for predictable results. What it does (function) Acts as a USB electronic load / discharge resistor designed for 5 V USB testing. Onboard resistors and switches allow three selectable resistance configurations: 2.2 Ω (10 W), 4.7 Ω (10 W), or both resistors placed in parallel. When the two resistors are used in parallel, the combined resistance is lower and the device produces a higher discharge current from a 5 V supply. Important specifications and formulas Selectable resistor values: 2.2 Ω, 4.7 Ω, or both in parallel. Power rating: each resistor is rated at 10 W. Designed to work with standard 5 V USB power sources. Parallel-resistance formula: R = 1 / (1/R1 + 1/R2 + ... + 1/Rn) Ohm’s law for current: I = V / R Example performance: with the two resistors in parallel on a 5 V supply, the device can generate an almost 3 A discharge current (actual current depends on supply voltage and exact resulting resistance; calculate using I = V / R). Compatibility and use notes Intended for use with USB 5 V power sources (power banks, phone chargers, USB ports). Calculate exact current and power dissipation before use to ensure the source and resistor ratings are not exceeded (use the formulas above). The device provides discrete, switch-selectable load levels rather than continuously variable current. Practical applications (use scenarios) Power bank capacity and stability testing: apply a steady USB load to measure discharge behavior and runtime under a known resistance. USB charger and port testing: verify that a charger or USB port can supply expected current at 5 V under realistic load conditions. Device thermal and power validation: reproduce repeatable load conditions to test heat dissipation, voltage regulation, and protection features of USB-powered equipment. What to check before use Confirm the USB power source can safely supply the expected current at 5 V. Use I = V / R to calculate actual current for the selected resistor configuration. Ensure the resistor power rating (10 W per resistor) is not exceeded in your chosen configuration and duration of test.