ATX Power Supply Boluo Xurong Electronics Co., Ltd. , https://www.greenleaf-pc.com
In the automotive electronics world, the environment is extremely demanding. Due to load transients and inductive field decay, the car’s battery voltage can fluctuate significantly—ranging from -12V DC (reverse polarity) to as high as 125V DC. These extreme conditions, combined with temperature variations, exposure to external elements, and potential ESD (electrostatic discharge) events from human interaction, make the operating environment far more challenging than typical consumer applications.
To meet these demands, the automotive industry requires cost-effective and highly reliable solutions. However, the harsh environment poses significant challenges for power semiconductor devices, which are essential for controlling various functions in modern vehicles. Standard MOSFETs often struggle to withstand the stress caused by inductive surges and load dumps, leading to the need for larger MOSFETs or external clamping circuits. Both options increase system complexity and cost.
Enter self-protecting MOSFETs—innovative components developed by companies like Diodes that integrate protection features directly into the device. These MOSFETs use a monolithic design that combines clamping and other protective functions, offering a more compact, reliable, and cost-effective solution for driving relays, LEDs, and other inductive loads in automotive systems.
For relay control, Diodes’ DMN61D8LQ is a self-protecting MOSFET in a SOT23 package optimized for automotive relay applications. It includes ESD protection on the input side and active clamping on the output. This is especially important when switching inductive loads like relays, as they generate large voltage spikes when turned off. Without protection, these spikes can damage the MOSFET.
The active clamp configuration uses a back-to-back Zener stack between the gate and drain of the MOSFET. The clamping voltage is set below the breakdown voltage of the drain-source junction but high enough to avoid triggering during normal operation. When the MOSFET turns off, the drain voltage rises above the Zener threshold, allowing current to flow through the Zener and input resistors. As the gate voltage approaches the threshold, the MOSFET begins conducting, safely dissipating the inductive energy instead of causing a destructive reverse breakdown.
This approach not only protects the MOSFET but also reduces power loss during clamping, improving overall energy handling capability.
For lamp drivers, self-protecting MOSFETs like Diodes’ ZXMS6004FFQ offer full protection, including overtemperature and overcurrent safeguards. They also feature input protection against overvoltage and ESD. Available in a compact SOT23 package, this device is six times smaller than its SOT223 counterpart, making it ideal for space-constrained automotive designs.
The built-in thermal shutdown circuit prevents overheating by turning off the MOSFET when the temperature exceeds a critical threshold (typically 175°C). Once cooled down, the device automatically recovers, ensuring long-term reliability. Overcurrent protection also plays a key role, limiting surge currents that can occur when incandescent lamps are turned on. The current-limiting circuit detects excessive VDS and reduces gate drive to protect the MOSFET and extend lamp life.
These protection mechanisms work together seamlessly, enhancing system robustness. Even if one feature is engaged, others remain active, ensuring comprehensive protection in all scenarios.
With internal protection features, self-protecting MOSFETs provide an efficient and reliable solution for automotive applications. Their compact size, enhanced performance, and built-in safety features make them a preferred choice for designers looking to improve system reliability while reducing costs and saving space.