WCS2702 Hall Effect Linear Current Sensor

This post is a quick writeup about Winson WCS Series Hall Effect Linear Current Sensors! I have the Winson WCS2702 current sensor in my hand right now, so I will write about it here.

Winson WCS2702

According to the Winson Datasheet, WCS2702 provides economical and precise solutions for both DC and AC current sensing in industrial, commercial and communications systems. The linear current sensor consists of a precise, low-temperature drift linear Hall IC with temperature compensation circuit and a current path typical with 98mΩ internal conductor resistance. Applied current flowing through the current path generates a magnetic field which is sensed by the integrated Hall IC and converted into a proportional voltage. Since the terminals of the current path are electrically isolated from the sensor leads, the WCS2702 current sensor can be used in applications requiring electrical isolation without the use of opto-isolators or other costly galvanic-isolation techniques.

This is the function block diagram of WCS2702 (borrowed from its datasheet):

WCS2702 Module

As usual, several Chinese WCS2702 modules are available online. This is a picture of a common WCS2702 module, with MCP6021 IC.

This is the basic schematic that I drew. There is no exact guarantee!

The voltage comparator circuit works as pointed below:

  • When VREF < AOUTDOUT = High & LED = OFF
  • When VREF > AOUTDOUT = Low & LED = ON

(VREF can be set by tuning the trimpot P1).

WCS2702 Overcurrent Detector

Even a quick evaluation of the WCS2702 calls for some additional electronics to render a sensible readout of the measured current. This is a brief description of the construction of a simple overcurrent detector based on the WCS2702 sensor. This is a closeup of my WCS2702 sensor.

The circuit below is built around a far-famed voltage comparator LM393 IC. It is responsible for taking the WCS2702 current sensor input. It also controls an optional switching mechanism to protect the connected load when an overcurrent condition takes place. The sensitivity (△VOUT) of the WCS2702 sensor is 1.0mV/mA ​​(typical), thus 1A current will give 1V output. Also note that the sensor has a quiescent (zero current) output voltage close to ½ VDD. The current range is DC: ±0 ~ 2A / AC: rms 1.4A.

I rigged up my circuitry on a common breadboard, and employed a regulated 5VDC power supply as the power source for the entire setup.

The WCS2702 is not a breadboard-friendly sensor, so I built a quick breakout board for the sensor to test my setup without taking pains. This is a closeup of that homemade breakout board.

To test the over current detector, I simply wired a 4V/3W white COB LED module to a variable DC power supply through the current sensor and applied regulated 5VDC to the breadboard. Then, I tweaked the trip-point by adjusting the trimpot P1 so that the overcurrent detection threshold is somewhat higher than the actual current consumption of the test LED. Last, I intentionally operated with high voltage to ensure that the circuit will respond right during an overcurrent condition. Yes, all things worked out as anticipated!

This is a simple overcurrent detector circuit with an option (DOUT) to drive an electromagnetic or solid-state relay which can work as a “trip-switch” (extra hardware needed). The analog signal output (AOUT) of this circuit can be used to monitor/measure the load current with the help of a microcontroller.

The AOUT is just a DC voltage relative to load current, but I should point it again that the output of WCS2702 on a 5V rail sits around 2.5V (½ VDD) while zero current flow through the sensor. So, at 2V delta, the final output should be close to 4.5V (you can add some analogue circuitry to null this out or do it in your code).

Current Sensing Theory

In principle, a proportional magnetic field is produced for a given current flow around the current carrying conductor. The Hall-Effect sensor has a core, Hall-Effect device and signal conditioning circuitry. The current conductor passes through a magnetically permeable core that concentrates the conductor’s magnetic field. The Hall-Effect device is mounted in the core at a right angle to the concentrated magnetic field. A constant current in one plane excites the Hall device. When the energized Hall device is exposed to a magnetic field from the core, it produces a potential difference that can be translated into a process-level signal.

In Conclusion

I have been experimenting with WCS2702 the past two weeks and it is a great linear current sensor available at an affordable price. I enjoy working with this compact sensor and have been using it in some projects. They are focused on portable battery charging applications. The main charm about this minuscule sensor is that it provides pretty perfect galvanic-isolation.

Furthermore, there are still a few things to do to make the most of the features of this sensor. Detailed write-ups and more do-it-yourself projects will be ready in a few weeks. Any thoughts on related projects? Let me know!

Credits (Most of what I still remember):

https://www.digikey.com/en/articles/the-basics-of-current-sensors

Leave a Comment