In this installment of the back-to-basics electronic component series, in partnership with EDN, we cover current sensors. Don’t miss our discussion with Michael DiGangi, executive vice president of Aceinna.
The need for performance monitoring in an advanced electronic product, regardless of the market intended, is paramount today. From predictive maintenance to fault discovery to disaster recovery, knowing what is going on under the hood is a critical performance enabler, and not having a complete handle on things can lead to everything from poor performance to catastrophic failure under stress conditions.
Know power, know performance
Many solutions are available to monitor the performance of an electronic circuit, and some involve advanced system infrastructure solutions using very sophisticated sensing devices and modules. The temptation is to procure the most sophisticated sensing technology available to address the application, but that runs the risk of your product not being as cost-effective as it could be. Current-sensing technologies offer a cost-effective way to perform this critical system oversight.
One fundamental aspect of an electronic circuit is often overlooked – it’s all about the power. Nothing happens unless there is energy in the wires, and everything stems from the electrical current driving the system. One can determine a great deal about any powered device by monitoring how it handles the power given it to perform a task.
Current-sensing technologies are key to creating the precision control and protection electronic circuits needed in a small footprint. Ironically, current-sensing is one of the cost-effective ways to monitor system performance in real time at a granular level. Knowing how your system is managing its power is as fundamental a diagnostic as a doctor knowing the heartbeat and blood pressure of their patient.
Current sensors, often tiny, are integral components in many of today’s most interesting and most critical technologies. (Source: Aceinna)
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Current events
There are essentially two ways to perform current sensing, open- or closed-loop. Open-loop current sensors measure AC and DC currents and provide electrical isolation between the circuit being measured and the output of the sensor. Less expensive than closed-loop designs, open-loop current sensors are generally used in relatively inexpensive products, given their low power requirements and small footprint.
On the other hand, closed-loop sensors measure currents with a feedback loop (e.g. feedback loop to operate at zero magnetic field) while providing electrical isolation, important in many circuits. Closed-loop current sensors, sometimes also called ‘Zero-Flux’ sensors, offer higher accuracy, faster response, high linearity, and low temperature drift and avoid core heating. Closed-loop sensors are often the sensor of choice when high accuracy of less than 1% across the full temperature range is critical to the design.
There are multiple current-sensing techniques however, and each has its strengths and weaknesses. Some of the popular methods include shunt resistors, current transformers, and magnetic-field based transducers, among others. One of the most common, cheap, and simple approaches is to use a shunt resistor, using the voltage drop across the shunt, which is proportional to the current flow. Able to measure both AC and DC, they have issues in that parasitic inductance negatively impacts measurement precision.
Current-sensing comparisons. Click for a larger image. (Source: Aceinna)
Current transformers can also be used but they are also passive devices, and a very high primary current or a substantial DC component in the current can saturate the ferrite material used in the core, ultimately corrupting the signal. Core losses also develop heat in the sensor, degrading performance. A ferrite-core-based current transformer has hysteresis and related challenges which degrade performance, unless demagnetized.
Hall-effect sensors produce a voltage output in the presence of a magnetic field perpendicular to the sensor, and so can monitor the field generated by a current-carrying conductor. However, it usually requires signal conditioning to make the output usable for most applications. Not only are signal-conditioning electronics needed, but voltage regulation is also required when operating from an unregulated supply.
Michael DiGangi, executive vice president at Aceinna, discusses the basics of current sensors, where they are used, and what specs are most important. If you’re using wide-bandgap power devices, you’ll want to hear what DiGangi has to say about AMR current sensors. – Gina Roos, editor-in-chief, Electronic Products.
AMR current sensing
Compared to the other methods of current sensing, an anisotropic magnetoresistive (AMR) sensor provides a high-performance solution over the operating temperature range. Presenting a single-chip solution, the Aceinna AMR-technology-based isolated current sensor does not require additional components, other than a decoupling capacitor.
Cutaway image of an Aceinna AMR-based current sensor. Click for a larger image. (Source: Aceinna)
Such a complete solution is superior to using a shunt resistor, which is inherently not isolated, and it is far smaller and more accurate than a current transformer, which only works with AC anyway. Compared to using other Hall-effect sensor solutions, AMR technology offers a wider bandwidth (1.5 megahertz), with lower offset and noise.
Since AMR technology can respond to both DC and AC bi-directional current, with better accuracy, higher bandwidth, and lower phase shift, than legacy solutions, it also offers a very fast output step response. An AMR-based current sensor is an accurate and compact solution for critical measurements to protect and control power systems.
This level of advanced current-sensing capability is highly empowering for performance-critical applications. These include next-generation high-efficiency power supplies, industrial systems (Industry 4.0), where the highest levels of efficiency and reliability are demanded; electric vehicles, which are under tremendous pressure to increase driving range, and green energy of all kinds to enhance grid utility. The bandwidth of Aceinna’s AMR current sensors enable the use of silicon carbide (SiC) and gallium nitride (GaN) power devices in similar applications. AMR current-sensing technology addresses and empowers these and other applications and industries.
Conclusion
There is an enormous amount of attention being paid to advanced embedded electronics right now, with much of the focus being on improving the efficiency of power supplies, motor drivers, the powertrain, and battery charging systems. They are all directly related to power performance, and by using advanced current sensing methodologies like Aceinna’s AMR-based current sensors, you can address the real-time monitoring needs of these advanced systems.
About the author
Michael DiGangi is Aceinna’s executive vice president, responsible for worldwide sales efforts. He brings with him over 26 years of power and analog IC semiconductor sales, business development and marketing experience spanning a number of larger corporations and startups. Prior to joining Aceinna, DiGangi was VP of sales and marketing for two startup SiC power semiconductor makers. Previously, he was vice president of worldwide sales and marketing at Allegro MicroSystems. DiGangi also was at International Rectifier, now Infineon, during the formidable growth of the company, with responsibilities as vice president of sales and number of senior sales and marketing management roles. He has a B.S. and an M.B.A from Wilmington University.
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