Embedded Systems and Design & Development - Feb 17, 2026 | Morning | VisionAstraa EV Academy

Battery Management Systems Overview

Introduction to Battery Management Systems (BMS)

• The session begins with a welcome and acknowledgment of technical issues that delayed the start.

• Discussion focuses on the preliminary functions of BMS, including sensing voltage, current, temperature, charging, discharging, and ensuring battery safety.

Key Functions of BMS

• Emphasis on measuring voltage as the primary requirement followed by current and temperature measurements.

• The session will cover various methods for measuring voltage and how this information is utilized for control purposes.

Cell Monitoring in BMS

• Introduction to cell monitoring as a critical function within BMS; it involves monitoring essential parameters like cell voltage, charge/discharge current, and thermal aspects.

• Accurate measurement of these parameters is crucial for controlling battery charging/discharging processes.

Signal Conditioning in BMS

• Explanation of signal type mismatch between analog sensor data and digital microcontroller requirements; highlights the need for an interfacing circuit.

• Interfacing circuits perform essential functions such as converting signal types and conditioning signals to remove noise before processing.

Types of Voltage Sensors Used in Automotive Industry

Common Voltage Sensor Types

• Overview of different types of voltage sensors starting with potential divider-based sensors which are simple and cost-effective but have limitations.

• Capacitive voltage dividers are introduced as another method using capacitors to measure voltage drops.

Advanced Voltage Sensing Techniques

• Transformer-based sensors utilize Faraday's law to convert high voltages into low voltages compatible with embedded controllers.

• Hall effect sensors are explained; they operate based on the principle that a magnetic field induces a potential across a conductor carrying current.

This structured summary captures key insights from the transcript while providing timestamps for easy reference.

Understanding Hall Effect Sensors in Electric Vehicles

Overview of Hall Effect Sensors

• Hall effect sensors can measure voltages and are commonly used in electric vehicle (EV) applications, particularly as variants designed for closed-loop systems.

• These sensors serve as crucial components in the EV industry, often integrated with isolation amplifiers or application-specific integrated circuits (ASICs) to monitor cell voltages and parameters.

Voltage Measurement Techniques

• The discussion transitions to various voltage measurement methods, starting with potential divider circuits that utilize resistors to split high voltage into manageable levels.

• A potential divider circuit typically consists of two resistors; the voltage drop across these resistors is critical for feeding data into analog-to-digital converters (ADCs).

Functionality of Potential Divider Circuits

• In a potential divider setup, high voltage is divided between two resistors (R1 and R2), allowing a small voltage drop across R2 to be measured by ADCs.

• The selection of resistor values is essential; proper design ensures that the output voltage fed into the ADC accurately reflects the input voltage.

Calculating Output Voltage

• The output voltage can be calculated using the ratio of R1 and R2 along with the input voltage. This relationship allows for precise control over what is read by the ADC.

• By rearranging terms based on Ohm's law, one can derive expressions for V_out from known values, ensuring safe feeding of voltages to ADC systems.

Transitioning to Capacitive Voltage Sensors

• Following potential dividers, capacitive voltage sensors are introduced as another method for measuring voltages within EV architectures.

• Hall effect sensors operate based on magnetic fields; they generate a measurable hall voltage proportional to current flow when placed in such fields.

Applications and Importance of Voltage Monitoring

Role in Electric Vehicles

• Accurate measurement of various voltages—such as cell voltages or DC bus voltages—is vital for effective operation within an EV's electrical system.

High Voltage Considerations

• Typical DC bus voltages in modern EV designs reach up to 400 volts, which helps reduce conductor stress while maintaining efficiency.

• Higher DC bus voltages (up to 800 volts in some designs) allow for smaller conductors, reducing weight and cost without compromising power delivery.

High Voltage Measurement Techniques in Electric Vehicles

Overview of Voltage Levels

• Discussion on high voltage levels in traction inverters, typically ranging from 390 to 410 volts, and the auxiliary supply at 12 volts for systems like infotainment.

• Mention of a potential 48-volt bus structure, highlighting the need for compatible measurement techniques due to higher voltages exceeding ADC input limits.

ADC Input Limitations

• Explanation of ADC limitations where input voltage must be within 0 to 5 volts or sometimes up to 3.3 volts, making direct measurement of higher voltages (like the 12V bus) incompatible.

• Introduction of voltage sensors as necessary tools for stepping down high voltages to meet ADC requirements.

Capacitive Voltage Sensors

• Description of capacitive voltage sensors that utilize capacitors instead of resistors for creating voltage drops, primarily used for measuring high AC voltages.

• Clarification that these sensors are not suitable for DC measurements and are specifically designed for high-tension AC applications.

Potential Transformers

• Overview of potential transformers based on transformer principles, which step down high AC voltages (e.g., from 400V).

• Emphasis on their exclusive use with AC sources; connecting DC will yield no output due to lack of magnetic flux change.

Signal Processing Challenges

• Discussion on the output nature from potential transformers being AC and its incompatibility with ADC inputs requiring DC signals.

• Various methods mentioned for converting bipolar AC outputs into unipolar signals suitable for ADC processing.

Hall Effect Sensors

• Introduction to Hall effect sensors featuring current-carrying conductors and their role in measuring electrical parameters related to current flow.

Understanding Hall Effect Sensors and Their Applications

The Basics of Magnetic Fields and Hall Effect Sensors

• A magnetic field is produced around a circular arrangement, which includes a ring structure with a small break that allows the magnetic field to pass through.

• When the magnetic lines of force contact Hall elements within this field, they generate a Hall voltage when current flows through these sensors.

• Although the primary objective is to measure voltage, enhancements in Hall effect sensor configurations allow them to also measure voltages effectively.

Enhancements for Voltage Measurement

• Adding an auxiliary coil to the Hall effect sensors creates a closed loop, enabling these sensors to function as both current and voltage measurement devices.

• High resistance resistors are connected at two points where potential difference is measured, ensuring minimal loading on the measurement point.

• This configuration induces an electromotive force (emf), generating a magnetic field that aids in measuring voltages using conventional Hall effect sensors.

Applications in Electric Vehicles

• Modified Hall effect sensors are commonly used in electric vehicles (EVs) for measuring DC bus voltage and auxiliary system voltages.

• These sensors provide precise measurements compared to traditional voltage sensors discussed earlier.

Exploring Opto-Isolated Voltage Sensors

Circuit Arrangement and Functionality

• Opto-isolated voltage sensors utilize light-emitting diodes (LEDs) connected through current-limiting resistors to measure potential differences against reference potentials.

• The intensity of light emitted by the LED influences the biasing of an optical transistor, controlling output voltage levels based on this light intensity.

Advantages of Electrical Isolation

• One significant advantage of opto-isolated sensors is their ability to electrically isolate high-voltage input sections from low-voltage output sections, enhancing safety during operation.

• These input sections can handle up to 400 volts while ensuring that faults do not propagate into lower-voltage areas like microcontrollers operating at 5V or 3.3V.

Integration into Electric Vehicle Architecture

• Isolation amplifier-based voltage sensors are primarily used in integrated circuit (IC)-based solutions within electric vehicle architectures for safe and effective voltage measurement.

Isolation Amplifier and Voltage Sensors in EVs

Overview of Isolation Amplifiers

• Isolation amplifiers provide electrical isolation, condition signals, and deliver them to the controller's ADC input in digital devices.

• The design includes three resistors for added protective features compared to earlier diagrams that only showed two voltage dividers.

Resistor Specifications

• Resistors R1 and R2 are typically in the megaohm range, while additional resistors may be in the kiloohm range.

• These resistor combinations ensure that voltages are safe for handling by isolation amplifiers.

Understanding Biasing in Transistors

• Bipolar Junction Transistors (BJTs) require current biasing at their base terminal; they are current-controlled devices.

• Optical transistors replace electrical bias with light rays, where the intensity of light determines the bias level.

Signal Isolation Techniques

• Clampers can be used for signal isolation; they function similarly to current transformers and allow flexible measurement around conductors.

• Discussion on clampers will continue when addressing current transformers later.

Application-Specific Integrated Circuits (ASIC)

• Custom-built solutions like isolation amplifier-based voltage sensors are essential for reliable operations in electric vehicles (EV).

• Dedicated ASICs monitor cell voltage and other parameters within battery management systems, available as IC packages for easy integration into system development.

Measuring Voltages in Electric Vehicles

Voltage Measurement Requirements

• Various voltages need monitoring within an EV: individual cell voltages, pack voltage, and DC bus voltage.

Lithium-Ion Cell Voltage Range

• The nominal voltage of a lithium-ion cell is 3.7V, with a maximum of 4.1V and a discharge limit between 3.1V to 3.6V depending on manufacturer specifications.

Sensor Selection for Voltage Measurement

• Discussion on which sensing methods—resistive or capacitive dividers, transformer-based sensors, Hall effect sensors—are suitable for measuring lithium-ion cell voltages within specified ranges.

Cell Voltage Measurement Options

Overview of Measurement Techniques

• The capacitive voltage sensor is not suitable for measuring cell voltage as it is designed for AC measurements.

• Potential coil and transformer-based solutions are also ruled out, leaving options like isolation amplifier-based sensors, Hall effect sensors, and resistor voltage dividers available for use.

• Dedicated IC-based monitoring solutions are commonly employed in Battery Management Systems (BMS), referred to as Cell Monitors (CMS).

Decision Criteria for Sensor Selection

• The choice between resistive voltage dividers, Hall effect sensors, or BMS monitoring ICs depends on the safety-critical environment where the measurement occurs.

• ISO standard 26262 outlines safety aspects relevant to automotive applications, emphasizing the importance of adhering to these standards during design decisions.

Understanding ASIL Levels

• Automotive Safety Integrity Level (ASIL) categorizes safety requirements from A (lowest) to D (highest), influencing sensor selection based on required safety integrity.

• For ASIL levels A or B, resistive voltage solutions may suffice; however, level D necessitates more reliable options such as isolation amplifiers or dedicated monitoring ICs.

Battery Pack Voltage Measurement

Sensing Options for Battery Packs

• Capacitive voltage sensors and transformer-based solutions are again ruled out for battery pack measurements due to their AC focus.

• Available sensing methods include Hall effect sensors and isolation amplifier-based sensors; dedicated IC solutions can also facilitate accurate measurements.

Traction Inverter Voltage Requirements

• The traction inverter powers electric motors in vehicles; understanding its DC bus voltage—typically around 400 volts—is crucial for effective operation.

• Variations in DC bus voltage require constant monitoring to ensure optimal performance of the motor being driven by the inverter.

Voltage Sensing in Electric Vehicles

Methods for Voltage Measurement

• Isolation amplifier-based sensors and voltage sensors are suggested methods for measuring voltage in electric vehicles, with the choice influenced by safety levels.

• Hall effect-based sensors are commonly paired with resistive voltage dividers to reduce voltage levels suitable for measurement.

• For AC voltages, capacitive voltage sensors or transformer-based sensors may be selected based on the application requirements.

Onboard Chargers Overview

• Onboard chargers contain converters and controllers within the electric vehicle, allowing them to manage AC supply from external sources.

• Understanding the available voltage at car inlet ports is crucial for selecting appropriate sensing solutions like capacitive or transformer-based sensors.

• A combination of different sensor types can also be utilized depending on specific needs.

Auxiliary Systems Voltage Measurement

• Auxiliary systems (e.g., lighting, horn systems, infotainment) have lower safety criticality, allowing simpler sensor solutions such as resistive dividers.

• Resistive divider-based sensors are cost-effective options for measuring voltages in auxiliary systems typically operating around 12V.

Considerations for Resistor Selection

• While resistive dividers are widely used due to their simplicity and cost-effectiveness, they have disadvantages related to resistor stability over time and temperature sensitivity.

• Standard wire-wound resistors may change value due to temperature fluctuations; thus, automotive-grade resistors should be preferred for reliability.

Overvoltage Protection Mechanisms

• The discussion transitions into protection aspects during charging lithium battery cells, emphasizing the importance of monitoring cell voltage closely.

• When cell voltage approaches critical thresholds (e.g., 4.1V), overvoltage protection mechanisms must activate to disconnect the charger if necessary.

Charging Isolation Mechanism for Lithium-Ion Cells

Overview of Charging Isolation

• The objective is to isolate a lithium-ion cell from the charger when its voltage reaches 4.1 volts, preventing overcharging.

• A semiconductor switch, akin to a BJT (Bipolar Junction Transistor), is used for this isolation, controlled by an embedded controller.

Control Mechanism

• The embedded controller determines when to open or close the switch based on feedback from a voltage sensor measuring the cell's voltage.

• As the voltage rises gradually from 3.1V to 4.1V, the controller processes this data and issues a control signal to open the switch at 4.1V.

Data Collection and Processing

• The process involves collecting data via a voltage sensor, converting it using an ADC (Analog-to-Digital Converter), and then making decisions based on that processed data.

• ADC plays a crucial role in converting analog signals into digital form for further processing by the embedded system.

Importance of ADC Specifications

• Understanding ADC specifications, particularly bit resolution, is essential for accurately representing voltage levels in digital format.

• For example, representing a DC signal requires knowledge of how many bits are necessary to capture specific values accurately.

Bit Representation in Digital Systems

• To represent numbers digitally, such as '5', three bits are required since two bits can only represent four values.

• However, detecting voltages with precision (e.g., increments of 0.1V up to 4.1V) necessitates more than three bits; thus higher bit counts are selected for better accuracy.

Conclusion on Bit Selection

• Using additional bits allows representation of both whole numbers and fractional parts effectively within specified ranges.

• This selection process ensures that all necessary information about cell voltage can be captured without loss of detail during conversion from analog to digital signals.

Understanding ADCs and Over Voltage Protection Mechanisms

The Role of Bits in Representing Analog Signals

• A bit can represent only two states (0 or 1), which limits precision when representing decimal or fractional information.

• To accurately represent analog signals in binary form, the number of bits used must be increased to enhance precision.

Types of ADCs and Their Impact on Accuracy

• Different types of Analog-to-Digital Converters (ADCs) exist, including 4-bit, 8-bit, 10-bit, and 16-bit options; higher bit counts improve accuracy.

• It is crucial for embedded systems engineers to determine the necessary accuracy and range for measurements when selecting an appropriate ADC.

Implementing Over Voltage Protection

• Over voltage protection requires a voltage sensor to detect voltage levels, which then needs conversion from analog to digital for processing by a microcontroller.

• Semiconductor switches like MOSFETs are essential for connecting or disconnecting battery cells from chargers as part of the over voltage protection mechanism.

Safety Considerations in Automotive Applications

• In automotive applications, safety standards (like ISO levels B or C) necessitate additional redundant mechanisms and fail-safes beyond basic disconnection logic.

• Components such as Transient Voltage Suppression (TVS) diodes and fuses are critical in ensuring safety during over voltage conditions.

Managing Charging Conditions and Transients

• During steady-state charging conditions, voltages remain relatively constant; however, transients can occur due to faults or malfunctions that require protective measures.

• TVS diodes act as protective devices against sudden surges in power by diverting excess voltage away from sensitive components like lithium cells.

Final Thoughts on Over Voltage Protection Components

• TVS diodes are placed parallel to battery cells to safeguard them during transient events while maintaining normal charging operations through semiconductor switches.

• Fuses serve as a last line of defense by melting under excessive current flow, isolating both load and source sides of the circuit.

Embedded Controllers and Their Peripherals

Overview of Embedded Controllers

• The session focuses on understanding embedded controllers and how to meet requirements using them. Discussion includes essential components needed for building these controllers.

Key Peripheral Functions in Microcontrollers

• Microcontrollers serve as embedded control devices, with specific peripheral functions crucial for automotive applications.

• Common peripherals include Analog to Digital Converters (ADCs), interrupt mechanisms, and timer counter mechanisms, which are standard across various microcontroller types.

Application-Specific Peripheral Functions

• Depending on the application category, additional peripherals like PWM controller modules and quadrature encoder pulse (QEP) modules may be included in microcontrollers.

• It is the responsibility of the embedded system design engineer to select appropriate microcontrollers based on required peripheral functions for specific applications.

Communication Needs in Automotive Systems

• In systems such as infotainment or status monitoring within vehicles, communication is a core function performed by embedded controllers.

• Essential peripherals must support frequent information exchange between different vehicle systems.

Understanding ADC Parameters

• When selecting ADCs, key parameters include resolution (number of bits representing analog signals), conversion speed, simultaneous signal processing capability, and voltage range compatibility.

Practical Considerations for ADC Selection

• A trade-off exists between higher output bit resolution and conversion speed/processing efficiency; typically 12-bit or 16-bit ADC resolutions suffice for battery pack measurements.

Voltage Measurement Compatibility

• For example, the ATmega328 microcontroller can measure voltages from 0 to VCC (e.g., 0 to 5 volts). Higher voltages (like a DC bus at 400 volts) need conditioning circuits to ensure compatibility with this range.

Signal Conditioning Networks Role

• Signal conditioning networks are responsible for ensuring that high input voltages are stepped down appropriately so they can be measured accurately by the ADC without exceeding its limits.

Understanding ADC Specifications and Lithium-Ion Cell Protection

Key Parameters for ADC Selection

• Understanding the specifications of interfacing circuits requires knowledge of the ADC's input voltage range, including maximum and minimum voltages.

• A 10-bit resolution allows for 2^10 states, meaning the minimum voltage detectable by the ADC is determined by this resolution.

• To make informed design choices, it’s essential to refer to specific parameters in lengthy datasheets rather than scrolling through hundreds of pages.

• Utilizing generative agents can streamline the process of extracting relevant data from datasheets; however, it's crucial to verify this information independently.

Over Voltage Protection in Lithium-Ion Cells

• Implementing over-voltage protection for lithium-ion cells is critical as exceeding normal voltage thresholds (4.1V or 4.2V) can lead to physical damage within the cell.

• Overcharging can accelerate aging, reducing expected life cycles from around 600–700 cycles down to potentially only 300–400 cycles.

• Higher voltages increase internal resistance and temperature, negatively impacting battery performance and capacity.

Voltage Management Strategies

• It’s important to maintain a safe voltage range for lithium-ion cells: typically charging up to a maximum of 4.1V or 4.2V and discharging down to about 3.0V or higher depending on chemistry specifics.

• Each cell in a battery pack must be monitored individually for both over-voltage and under-voltage conditions using appropriate sensors paired with embedded controllers.

Trade-offs Between Capacity and Life Cycle

• Increasing charge voltage enhances capacity but reduces cycle life; e.g., charging at 4.3V yields full capacity but fewer cycles compared to charging at lower voltages like 3.9V which significantly increases cycle life (up to six times).

• A balance must be struck between maximizing charge voltage and extending battery life; finding an optimal intersection point (e.g., stopping at 4.1V).

Future Discussions and Queries

• Upcoming sessions will include practical demonstrations on programming microcontrollers for managing cell voltages effectively when reaching set thresholds like 4.1V.

• Questions regarding nominal voltages (typically around 3.7V), fully charged limits (up to 4.2V), and cutoff settings should ideally be clarified with manufacturers or OEM suppliers.

This structured overview encapsulates key insights from the discussion on ADC specifications related to interfacing circuits as well as critical considerations surrounding lithium-ion cell management strategies, particularly focusing on over-voltage protection mechanisms and trade-offs between capacity enhancement versus lifecycle sustainability.

Transient Voltage Suppression with TVS Diodes

Overview of TVS Diodes

• TVS (Transient Voltage Suppressor) diodes are utilized to protect circuits from transient voltage spikes, ensuring that the battery cell remains undamaged.

• These diodes can be implemented in various applications where transient suppression and safety are critical.

• The discussion emphasizes the versatility of TVS diodes, highlighting their importance in safeguarding electronic components against unexpected voltage surges.

• The session concludes with a summary of the protective role that TVS diodes play in electronic circuit design.