Harnessing Energy: A Journey Through the Ages
Pinkesh Sachdev, a product marketing engineer at Linear Technology, part of Analog Devices, dives into the role of monitoring and switching power in cars.
Today’s cars come packed with electronics powering heated seats, air conditioning, navigation, infotainment, and safety features, enhancing comfort and the overall driving experience. It’s hard to imagine, but just over a century ago, cars had no electrical components. They were started with hand cranks, used acetylene gas for headlights, and had bells to warn pedestrians. Fast forward to now, and vehicles are on the verge of becoming fully electrical systems with minimal mechanical parts, essentially transforming into high-tech digital devices.
This shift is driven by the need to reduce oil dependency for availability and environmental reasons and to boost safety in combustion, hybrid, and electric vehicles. As cars swap out mechanical systems for electronic ones, monitoring and managing power consumption becomes crucial. Keeping a close eye on power use in an electric vehicle reassures drivers and helps extend battery life.
Anyone who has driven an electric car has likely experienced range anxiety—the fear of the battery dying before reaching a destination. Unlike hybrid car owners, who can rely on a gasoline engine, electric car drivers have to find charging stations, which can be scarce and time-consuming. Therefore, continuously and accurately monitoring the power use of each electronic system is vital. This data can help drivers optimize battery life and extend their driving range.
Additionally, disconnecting idle modules from the power supply can save energy. Monitoring the current and power levels of sub-systems can also detect abnormal trends, predicting potential failures, and alerting the need for maintenance before problems occur.
The advantages of monitoring power and energy extend to diagnostics. Fault logging and wireless access to data facilitate quicker repairs, lowering costs and reducing downtime.
Monitor and Control
To keep track of an electronic system’s power consumption, continuous measurement of both current and voltage is required. Voltage is directly measured using an analog-to-digital converter (ADC). If the ADC input range is lower than the monitored voltage, a resistive divider might be needed.
For current measurements, a sense resistor is placed in the power path to measure its voltage drop. A transconductance amplifier then converts this high-side sense voltage into a current output, which passes through a gain-setting resistor, creating a ground-referenced voltage proportional to the load current. This voltage is suitable for feeding into an ADC.
To minimize power loss, the sense voltage is kept to just a few tens of millivolts, requiring an amplifier input offset better than 100µV. Power calculation involves multiplying the voltage and current readings, which a microcontroller or processor can manage via ADC data. Monitoring energy consumption entails accumulating (adding) these power readings over time.
When it comes to switching power, automotive circuits traditionally use electromechanical relays. However, to save space, these relays are often replaced with solid-state switches like n-channel and p-channel MOSFETs. This change allows all components to be placed on the same printed circuit board (PCB) and assembled through a single solder reflow process.
