The overload protection mechanism of a desktop charger is a core design element ensuring the safety of both the device and the user. Its activation relies on a sophisticated current monitoring and rapid response system. When the power of a connected device exceeds the desktop charger's rated output capacity, the protection mechanism, through the coordinated efforts of multiple components, cuts off the power supply within milliseconds, preventing equipment damage or fire risks caused by overload. This mechanism involves three key stages: hardware detection, logical judgment, and physical execution, with each component working closely together to form a complete safety loop.
Current detection is the fundamental component of overload protection. Desktop chargers integrate high-precision current sensors, typically employing Hall effect elements or magnetoresistive principles, to sense the current intensity in the output circuit in real time. These sensors convert the current signal into a voltage signal and transmit it to the control chip for analysis. When the charging demand of devices increases, the current sensor detects an upward trend in current; for example, when charging multiple mobile phones or tablets simultaneously, the total current may approach the desktop charger's rated value. At this time, the sensor continuously monitors current changes, providing data support for subsequent judgments.
The control chip, as the "brain" of the protection mechanism, undertakes the core functions of logical judgment and command issuance. When the data transmitted by the current sensor exceeds a preset safety threshold, the chip immediately activates the protection program. This threshold is typically set to 1.1-1.2 times the rated output current of the desktop charger, leaving a reasonable margin to avoid false triggering. For example, a desktop charger with a rated output of 5A might have its overload protection threshold set at around 5.5A. The control chip quickly determines whether an overload has occurred by comparing the real-time current with the threshold; this process is completed within microseconds to ensure rapid response.
After the protection is triggered, the actuator quickly disconnects the circuit connection. Common execution methods include electronic switch disconnection and physical relay activation. Electronic switches typically use power devices such as MOSFETs or IGBTs, achieving rapid switching through the level signal output by the control chip. When an overload is detected, the chip immediately outputs a low-level signal, reducing the MOSFET gate voltage and switching the device from the on state to the off state, physically cutting off the current path. Physical relays, on the other hand, achieve circuit breaking by the activation and deactivation of contacts through an electromagnetic coil. Although the response speed is slightly slower than that of electronic switches, they can withstand higher voltages and currents, making them suitable for high-power desktop charger designs.
Some high-end desktop chargers employ a dual-level protection strategy to enhance safety. Primary protection uses an electronic switch for rapid response, immediately cutting off power when the current just exceeds a threshold. Secondary protection consists of a physical relay; if the electronic switch fails to cut off power due to a malfunction, the relay will activate after the current continues to exceed the limit, providing double protection. This design ensures that even if one protection mechanism fails, the system can still cut off power through another path, greatly improving the reliability of overload protection.
After overload protection is activated, the desktop charger enters a locked state, requiring manual reset or re-plugging to restore power. This design prevents repeated power-on before the fault is resolved, thus preventing secondary damage. Some smart desktop chargers also have an automatic recovery function, restarting output after a few seconds delay once the current returns to normal. However, such designs require rigorous testing to avoid frequent start-stop cycles during current fluctuations, which could affect the device's lifespan.
In practical applications, overload protection mechanisms must work in conjunction with short-circuit protection, over-temperature protection, and other safety functions. During a short circuit, the current can reach tens of times the normal value, requiring the protection mechanism to respond in a much shorter time. Over-temperature protection monitors the internal temperature of the desktop charger using an NTC thermistor to prevent overheating from causing safety hazards. These protection functions together constitute the safety protection system of the desktop charger, ensuring effective protection of the equipment and user safety under various abnormal operating conditions.
