thermal overload protector in motor_mini cooper fuse box factory

26 2024-08

　　PPTC for overcurrent protection

　　PPTC is a non-linear, temperature dependent resistor. In general, PPTC components have extremely high conductivity, so the circuit can operate normally. But when an overcurrent condition occurs, this high current will generate enough energy (Joule heating effect) on the PPTC component to exceed its transfer temperature, causing a resistance bounce of 104 to 106 times. Therefore, overcurrent conditions can be eliminated to achieve the goal of protecting circuits and components.

　　In the USB 3.0 specification, it is explicitly required to use current limiting components as protection for the power supply end, and PPTC components and low-voltage semiconductor switches are often used as solutions for this current limiting. Most of the time, based on various considerations, engineers prefer to use PPTC components to prevent circuit damage. Because the available current has increased in USB 3.0, current limiting components need to pass more current while maintaining a certain voltage drop. Table 1 shows the comparison between PPTC components and low-voltage semiconductor components in USB 3.0 applications, which have advantages in terms of price, resistance, maximum fault current energy, and electrostatic sensitivity.

　　Compared to USB 2.0, USB 3.0 has established a new power management structure and defined new connection states and mechanisms to achieve better overall power efficiency. In terms of power supply allocation, the 3.0 specification is roughly the same as the 2.0 specification, but it increases power demand and relaxes voltage drop requirements. After completing the initial setup with the host, the SuperSpeed device can use a current of 900mA. In terms of power supply voltage requirements, the root connection port on the host or the connection port on the HUB has been reduced from the original 4.75V to 4.45V, and devices powered by USB must operate normally at 4.00V. Other regulations such as instantaneous current limitation, current limitation in host sleep or standby mode, etc., except for updating the current configuration to 150mA or high-power 900mA, all other requirements are as rigorous as the old specifications.

　　At present, new PPTC components have emerged in the industry for overcurrent protection of USB 3.0, ensuring that the design complies with the USB 3.0 specification requirements. For example, although USB 3.0 reduces the voltage requirements at the power supply end, the new generation of PPTC components can still ensure that the voltage drop of PPTC does not exceed 0.1V at full current load. In addition to ensuring compatibility with USB 2.0 devices, it also leaves greater design margin for other components or circuits on the motherboard. In addition, the new generation of overcurrent protection components can maintain full current load and not operate at high temperatures above 50 ℃, avoiding the misoperation of PPTC components due to thermal derating, especially in the back-end USB ports of desktop computers.