LEM has expanded its range of miniature, integrated circuit sensors for AC and DC isolated-current measurement with the introduction of their new HMSR series. Despite being a small size, these components can handle overload current bursts up to 20 kA (8-20 µs surge test profile), such as those that occur in photovoltaics applications, while still providing a reinforced isolation. Products in the series are designed to measure currents up to 2.5 times their nominal ratings 6 A, 8 A, 10 A, 15 A, 20 A or 30 A.
Packaged as SO-16 surface-mounted devices with a height of just 6 mm, HMSR sensors can be mounted directly onto printed circuit boards using the same process as other board-level components. This helps to reduce manufacturing costs and decrease the overall footprint, which is vital for applications with space limitations. As a result, HMSR sensors can be readily built into small form-factor intelligent power modules (IPMs).
The HMSR series uses a proprietary open-loop Hall effect ASIC associated with a unique low-resistance primary conductor to minimize power losses that allow direct current measurement and high transient overload currents to pass without damage. The use of ferrite for the magnetic element is a key factor in achieving a high frequency bandwidth of 270 kHz (-3dB) and to provide good rejection against external fields. The unique mechanical design for the sensor leads to creepage and clearance distances of 8 mm when using materials with a comparative tracking index (CTI) of 600, enabling reinforced isolation according to the IEC 60950-1 standard.
An integrated electrically erasable programmable read-only memory (EEPROM) is used for programmable internal temperature compensation to counter offset and gain drifts while performing gain stress compensation. These measures ensure high-performance accuracy over the full temperature range (-40 to +125°C) with a typical value of 0.5% of IPN for the HMSR 20-SMS model, marking a significant improvement over the previous generation. The HMSR series also achieves a shorter response time: 2 µs typical.
The output signal from the sensor is an analogue voltage, and sensitivity levels are determined by each model. For the 5V power-supply versions, output voltage is 800 mV @ IPN. As standard, devices in the HMSR range provide two different over-current detection (OCD) warning levels on two dedicated pins: one threshold is set during manufacturing at 2.93 x IPN; the other can be adjusted by the user using external resistors.
The HMSR series is ideal for demanding applications such as photovoltaics, which require high insulation levels together with stringent controls on price and product size. Similarly, the small size benefits applications such as drives for white-goods, window shutters and air-conditioning systems. HMSR can support high frequency currents thanks to the use of ferrite as a magnetic circuit with low losses, which suits drives that operate with higher switching frequencies. Additionally, the HMSR series’ low cost makes the device competitive against shunts with the added benefits of high insulation and OCD features. HMSR series conforms to the latest industrial standards, and all devices are covered by LEM’s five-year warranty.