As we all know, traditional fuel-powered vehicles can use waste heat from the gasoline engine to heat the cabin or the battery. However, new energy vehicles lack an engine and lack a heat source, so they require a PTC (Positive Temperature Coefficient) heater for active heating. PTC heaters are a key component in new energy vehicles that compensate for the lack of engine waste heat. They provide heat to the battery and cabin through self-limiting temperature electrothermal conversion and are currently one of the core heating solutions in new energy vehicle thermal management systems.
PTC heaters can be divided into air heating type (wind heating type) and liquid heating type (water heating type). The core principle is: when current passes through the PTC element, the resistor generates heat due to the Joule effect, and the heat is transferred to the battery pack (insulation at low temperatures to improve charging and discharging efficiency) or the passenger compartment (heating) through the air or coolant medium; and as the temperature rises, the resistance of the PTC element will increase sharply and nonlinearly, automatically limiting the current output to avoid local overheating, thus achieving "self-limiting temperature" protection.
It is worth mentioning that PTC heaters usually operate in high-voltage DC circuits (such as 400/800V power battery DC voltage), while control units (such as MCU, sensors) belong to low-voltage circuits (12V/24V on-board low-voltage system). Therefore, effective electrical isolation measures must be taken to prevent high voltage from entering the low-voltage system and damaging sensitive components, and to protect the lives of drivers and passengers, while meeting strict electrical safety design specifications.
The working principle of the PTC heater in new energy vehicles is that after the owner or the system issues a heating command through the CAN/LIN bus, the MCU/DSP starts to drive the IGBT or other power tubes, thereby controlling the PTC heater to conduct high voltage electricity for heating; usually, multiple PTC resistors are integrated in the PTC heater, and the system can achieve multi-level power output by controlling the on and off of different numbers of resistors, flexibly matching the different needs of cabin heating or battery heating.
As shown in the figure above, in the electrical isolation solution for PTC heaters in new energy vehicles, the PTC heater (HTR) is powered by the vehicle's high-voltage battery platform (HV) , and the MCU/DSP is powered by 5V DC. The two are mainly powered by an isolated driver chip and an isolated sampling chip to achieve safe coordination between low-voltage control and high-voltage heating.
Among them, the isolation driver chip is responsible for amplifying and improving the driving capability of the low-voltage control signal from the MCU/DSP under the premise of achieving electrical isolation, so as to efficiently drive the conduction/shutdown of the high-voltage side PTC heater power circuit; the isolation sampling chip is responsible for accurately collecting the phase current/bus current signal of the high-voltage side PTC heater under the premise of achieving electrical isolation, providing a logical basis for the MCU/DSP to accurately control the PTC heater (such as power regulation, fault protection, etc.) .
The digital isolation/isolation interface chip is responsible for completing the signal interaction between vehicle buses such as LIN/CAN and the MCU/DSP under the premise of achieving electrical isolation, so that the MCU/DSP can safely coordinate with other vehicle systems through these communication interfaces and accurately and efficiently control the operation of the PTC heater.
the core of PTC safety in new energy vehicles , the core value of digital isolators lies not only in achieving electrical isolation between high and low voltage circuits , but also in building a multi-layered protective barrier for the safe operation of PTC heaters through stable and reliable signal transmission, accurate and efficient parameter sampling, and anti-interference capabilities.
However, to fully realize the core value of digital isolators , they need to have a sufficiently high isolation voltage to resist the risk of high-voltage crosstalk, as well as strong anti-electromagnetic interference capabilities and long-term reliability to adapt to the complex in -vehicle environment.
For example, Huapu Micro's independently developed CMT812X (2-channel), CMT804X (4-channel) and CMT826X (6-channel) series of standard digital isolators not only support up to 5 kVRms isolation voltage, 8kV surge capability and an expected service life of more than 40 years, but also significantly enhance the device's electromagnetic compatibility (EMC), effectively meeting system-level ESD, EFT, surge and radiation compliance requirements.
The CMT8602X series of reinforced isolated dual-channel gate drivers not only feature 4A peak source current and 6A peak sink current, but can also drive power MOSFETs, IGBTs, and SiC MOSFETs up to 5MHz with best-in-class propagation delay and pulse width distortion.
The CMT130X series of isolated sampling chips not only effectively blocks high-voltage current and electromagnetic noise from being transmitted to low-voltage circuits, but also provides the MCU with high-precision real-time signals such as sampled current, voltage, and temperature to support the efficient and reliable operation of PTC heaters.
The CMT104X series of high-reliability isolated CAN transceivers not only provide ±70V DC bus fault protection and a ±30V common-mode voltage range, but also support data rates up to 5Mbps (CAN FD mode) for faster data transmission.
Looking ahead, as new energy vehicles accelerate their evolution toward higher voltage, intelligence, and lightweighting, PTC heaters will face challenges with higher power density, faster response speed, and more stringent safety standards. Digital isolators will continue to upgrade toward high integration, low power consumption, and intelligence while maintaining high isolation performance, in order to continuously meet the safety requirements of new energy vehicle thermal management systems and contribute to the high-quality development of the global new energy vehicle industry.
