Super Clamp TVS structure

Introduction

The electric vehicle (EV) market is experiencing rapid growth, providing a more environmentally friendly mode of transportation. While traditional vehicles require gasoline from gas stations, EVs simply need to be plugged into a charging station to recharge their batteries.

The on-board charger (OBC) is a critical component installed in EVs. It converts external AC power from the charging station into DC power (output voltage varies based on the EV’s battery specifications) to charge the battery. If the charging station provides DC power, this conversion step is bypassed, and the DC power is directly connected to the vehicle battery.

Supplementary Restraint Systems, (SRS), more commonly known as airbag systems, have been a standard feature in vehicles for over 40 years. These have evolved from simple frontal airbags to more comprehensive systems that include side curtain airbags and knee airbags. As a critical component of vehicle safety, the airbag control unit (ACU) plays a pivotal role in determining when to deploy the airbags.

The ACU receives electronic signals from various sensors, including impact sensors and accelerometers, which monitor the vehicle’s speed, acceleration, and other physical parameters. When these parameters exceed predefined thresholds, the ACU initiates the deployment of the airbags by igniting the gas generator within the airbag module.

According to the latest research, the automotive industry is estimated for a significant shift. By 2025, the value of electronic components in high-end vehicles is projected to surpass $6000, driven by the increasing sophistication of vehicle features. This trend is expected to accelerate if the EU successfully bans the sale of internal combustion engine vehicles by 2035, leading to an even higher proportion of electronic components in electric vehicles.

Despite the technological advancements in electric vehicles, the demand for robust and reliable automotive electronic components remains paramount. The failure of electronic control systems during driving can pose serious safety risks to passengers.

A critical component in the vehicle’s electrical system is the reverse polarity protection circuit. This circuit safeguards the battery and other sensitive electronic components from damage caused by reverse current, which can occur due to human error, external forces, or environmental factors. The ISO-16750-2 4.7 standard outlines specific safety requirements for transient reverse voltage testing.

One common design for reverse polarity protection circuits involves a series diode. While this method is simple, it results in significant power dissipation due to the voltage drop across the diode. For higher-power applications, MOSFETs are used to reduce power losses. Figures 2 and 3 illustrate the use of P-channel and N-channel MOSFETs, respectively. Although MOSFETs offer improved efficiency, they typically require more space and increase overall design costs.

When a battery applies reverse polarity, the diode becomes reverse biased, preventing current flow. Similarly, in MOSFET-based circuits, a reverse input voltage causes the MOSFET channel to close, effectively blocking the current.

Automotive lighting plays a crucial role in ensuring road safety. Adequate lighting, especially during nighttime driving, enhances visibility and provides drivers with a clear view of the road.

LEDs (Light Emitting Diodes), which convert electrical energy into light, have become the preferred choice for automotive lighting due to their numerous advantages, including low power consumption, long lifespan, high luminous efficiency, and environmental friendliness. LEDs find extensive applications in various automotive systems, and with the rapid growth of intelligent lighting, they can be broadly categorized into front and rear lighting. Front lighting includes headlights and fog lights, while rear lighting encompasses taillights, brake lights, reverse lights, and turn signals.

Headlights/Fog Lights

Protection Device: During the installation or repair of a vehicle, reverse connection of the car’s power supply can easily damage the vehicle’s controller due to reverse voltage. To address this issue, automotive regulations have introduced requirements for reverse polarity protection. This protection circuit primarily consists of diodes, TVS diodes, and MOSFETs.

DC/DC Converter: Headlights and fog lights, being high-power automotive lighting components, often utilize DC/DC converters to improve system conversion efficiency. Three common types of DC/DC converters used in automotive lighting are buck converters, boost converters, and buck-boost converters. The basic structure diagram is as follows:

Did you know that electric vehicles actually predate gasoline-powered cars? While there’s some debate about whether the first electric vehicle was invented in 1832 or 1881, it’s clear that it came before Karl Benz introduced the first gasoline-powered car in 1886. In fact, electric and gasoline cars were neck and neck in popularity around the early 1900s. However, the rise of the petroleum industry in the 1920s made gasoline significantly cheaper, and the internal combustion engine has dominated the automotive industry ever since. Electric vehicles became a mere footnote in automotive history.

The Importance of BMS

Despite this, electricity remains a crucial component of modern vehicles. In electric vehicles, power management is even more critical. If the battery is the heart of an electric vehicle, then the Battery Management System (BMS) is its brain. The BMS controls and monitors the electric vehicle’s power, ensuring optimal battery performance, longevity, efficiency, and most importantly, safety. It monitors the battery system to prevent issues like overcharging, over-discharging, and short circuits.

An electric vehicle’s power comes from a high-voltage lithium-ion battery pack composed of numerous cells connected in series and parallel. This battery can be charged directly using a DC fast charger or indirectly using an AC charger and the vehicle’s on-board charger (OBC), which converts AC power to DC power. The high-voltage battery can directly power high-voltage components like the motor inverter or air conditioning inverter, or it can be converted to 12V by an auxiliary power module (APM) to power lower-voltage components like the vehicle’s computer, lights, and wipers.

To protect the high-voltage battery from damage, the BMS, which includes components like transient voltage suppressors (TVS) and diodes, manages charging and discharging, selects power sources, and monitors and protects the battery system.

In the history of automotive development, aside from the evolution of power output, the most significant investment in research and development has been dedicated to providing drivers and passengers with more comprehensive safety protection. Initially, this focused on passive safety features such as airbags, seatbelts, and crumple zone design. With the rapid advancement from microcomputers to automotive computers, the focus shifted to active safety design, giving rise to the concept of Advanced Driver Assistance Systems (ADAS).

While ADAS features like Anti-lock Braking Systems (ABS) have been around for a longer time, the concept of driver assistance has been applied for even longer. As early as 1995, BMW introduced the Park Distance Control (PDC) system in the E38 model, which used ultrasonic signals to help drivers understand the distance between the vehicle and front and rear obstacles during parking, preventing collisions. This marked the beginning of the development of systems that actively influence driver control based on detected vehicle environment data.

Modern ADAS systems are generally divided into three parts: sensors, processors, and actuators. First, sensors such as cameras, radar, ultrasonic sensors, and even more expensive LiDAR are used to measure the distribution of the vehicle’s surrounding environment using light, images, and sound waves. These sensors are typically installed on the front and rear bumpers, windshield, and side mirrors, with the number of sensors depending on the vehicle’s ADAS configuration. According to the SAE International standard, the lowest level, Level 0, has no automated driving functions and only provides driving assistance information. For example, the commonly used Around View Monitoring (AVM) system only requires the installation of cameras and short-range radar.

ADAS is not synonymous with autonomous driving but is a prerequisite for achieving it. Processors and actuators play a crucial role in self-driving technology at Level 1 and above. In addition to displaying the sensor data for driver reference, the data is also transmitted to the processor, where the Electronic Control Unit (ECU) analyzes it and makes decisions, which are then transmitted to the actuators to control the throttle and steering wheel, enabling partial or fully automated vehicle control. For example, the Level 2 Automatic Parking Assist (APA) system only requires the driver to control the throttle, while the actuator operates the steering wheel.

Market sales data and public information show that Level 1 and Level 2 self-driving technologies will remain the mainstream for the next five years. Cameras and ultrasonic sensors are the primary components. Although cameras rely on software to simulate human visual perception to judge the environment, they are susceptible to weather and light conditions. However, compared to radar and LiDAR, cameras are less expensive and can be installed at multiple angles on the vehicle to obtain a complete view of the environment, making them the current mainstream configuration for ADAS.

Cameras provide image information and are therefore called image sensors (CIS: CMOS Image Sensor). The captured color image is divided into red, green, and blue pixels by a filter and enters the CIS. The CIS, based on its resolution and pixel design, has a corresponding matrix. Each pixel is a photodiode. When a photodiode receives light, it is converted into an electrical signal, which is transmitted through CMOS switches as an analog signal to the next component, the analog front-end (AFE), where it is converted into a digital signal and then processed by an image signal processor (ISP) to generate an image, which is then transmitted to the processor SoC (System on Chip) for calculation, judgment, prediction, and even learning. The conversion from analog to digital signals requires extremely fast speed and low interference, allowing the SoC to accurately interpret the data in real-time and provide the necessary parameters for the backend actuator to operate, assisting the vehicle in steering and power system driving.

CMOS Image Sensor and Signal Processing

With the rapid development of ADAS, there is a need for stable and fast electronic signal transmission. As the amount of information transmitted increases, more power is required. Since ADAS has multiple processors, such as PCIE Switch, Security ECU, etc., to avoid interference between different controllers when problems occur, each processor requires a separate power supply. Additionally, to meet the requirements of down-conversion and reducing electromagnetic interference (EMI) within a limited space, power supply circuits often use Power Management ICs (PMICs), which integrate DC/DC converters and low dropout regulators (LDOs) and have a smaller footprint. For example, as mentioned earlier, if the CMOS image sensor encounters problems with image acquisition due to freezing at low temperatures, a heater is used to heat the CMOS sensor, and the power for the heater needs to be provided by a boost converter. The boost converter uses MOSFETs as switching elements.

As automobiles become increasingly intelligent, drivers expect more than just basic driving functions; they desire a more humanized and convenient driving experience, such as automated parking assistance and keyless entry. In recent years, with the expansion of the electric vehicle market, the automotive industry has become highly reliant on semiconductors for its power systems. The Body Control Module (BCM) is a crucial component in automotive engineering, serving as a central hub that integrates various functions and facilitates data exchange between different electronic devices, ensuring driving safety and comfort.

The BCM, also known as the Body Computer, is the management center and information hub of a vehicle, comparable to the human brain or the CPU in a computer. It receives external signals and controls the body systems, responding with appropriate functions. The scope of its control has expanded significantly over the years, encompassing body devices (windows, wipers, mirrors), safety devices (anti-theft systems, remote start), lighting systems (LED headlights, fog lights, indicators), fuel pumps, and heating and air conditioning systems.

The diagram below illustrates the solutions provided by Taiwan Semiconductor at different stages of the BCM.