Switching regulator supplies microprocessors from a 4-20mA loop

Louise Smyth

RECOM has developed a switching regulator specifically for supplying microprocessors from the 4-20mA loops that are common in industrial systems.

The R420-1.8/PL is a flat module with extremely low idle power and high efficiency.

Supplying digital components from the unused portion of the loop current had become an issue with microprocessors processing raw data and HART (Highway Addressable Remote Transducer) modems ensuring that smart sensors keep sending a variety of data signals on the same loop.

Conventional switching regulator ICs are unsuitable as their high efficiency at full load drops so far at lower loads that they exceed the 4mA threshold. Low quiescent current in sleep mode cannot compensate as this and so the regulator shuts off the main output voltage altogether. Linear regulators are not ideal either; despite their perfectly decent quiescent current levels at around 0.5mA, poor efficiency decreases available power by a factor of around three compared to switching regulators.

The R420-1.8/PL switching regulators use a novel topology to lower the idle current to around 100μA while still maintaining rated voltage at output.

For example, 24VDC and <3.5mA at the input provides 3.3V and 10mA at the output, which can supply a sensor alongside the microcontroller and HART modem without affecting loop functionality or metering accuracy.

Another benefit is that these new switching regulators are programmable for any output voltage between 1.8V and 5V by simple wiring using a resistor. This provides a single component suitable for a variety of tasks in process automation or sensor-controlled, solar-powered systems.

The new R420-1.8/PL features an open-frame SMD design, operates at temperature range from -40°C to +105°C, and operates at an altitude of up to 5,000m. The regulator is permanently protected against short-circuit, and comes with a three-year warranty.