Improved shunt measurement techniques

The five new HLSR transducers in the series will satisfy application requirements in, for example:

• industrial inverters and motor drives
• switch-mode and uninterruptible power supplies
• specialist power supplies such as welding units
• air conditioning; home appliances
• renewable-energy systems, such as solar combiner boxes and solar inverters to track the maximum-power-point (MPPT).

The HLSR series uses Open-Loop Hall-Effect current sensing, to measure AC, DC or pulsed currents with nominal values of 10, 20, 32, 40 or 50A(rms). The devices achieve a response time of only 2.5 microseconds, with very low gain and offset drift over their operating temperature range of -40 to 105°C.

Open-loop transducers use the simplest implementation of the Hall-effect. They provide the smallest, lightest and the most cost-effective current measurement solution whilst also having very low power consumption. A current flowing in a conductor creates a magnetic field around the conductor. This field is concentrated by a magnetic core. The core has a gap cut through it and a Hall cell is used to sense the magnetic flux density in the gap.

Solid-state device

The Hall generator is a four-terminal solid-state device most commonly made of a thin film of silicon, germanium, indium arsenide, indium antimonide or gallium arsenide. Two leads provide the voltage output, the other two require a voltage or current source input. The voltage output is a differential voltage between the two leads that is dependent on the normal magnetic field and the control current flowing through the input leads.

The output from the Hall device is then signal conditioned so that the transducer output is an exact representation of the primary current.

In this way, HLSR transducers deliver their output as an analogue voltage proportional to the primary measured current. In most applications, this voltage will be converted to a digital value by an analogue-to-digital converter.

The HLSR is equipped with an internal voltage reference of 1.65 or 2.5V made available on a dedicated pin for use by an external device such as A/D converter; alternatively designers can choose to use an external reference from 0.5 to 2.65V. Special versions operate from either + 3.3 or + 5 V single supplies.

Typical accuracy is +/-1% at +25C, and +/-3.4% at 105C, with a bandwidth of 100kHz (-3 dB).

The five models are packaged in a compact and innovative outline that occupies only 387mm<2> of PCB area, less than many alternatives based on resistive shunts.

Variants of the package cater for either surface-mount or through-hole connection of both primary conductor path and signal/power connections. The low-profile package weighs just 5.5g, and is less than 12mm high.

Safe measurements are assured with a high level of insulation between primary and measurement circuitry thanks to long creepage and clearance distances (8mm as standard, but exceptionally 14mm.

Methods of Current Measurement