Hall effect current sensor to sense 10mA current

Hi Hardik

Thank you for your query. We are currently out of the office and will get back to you on Monday.

Hello Hardik,

10mA would produce a low magnetic field that would be difficult to measure with a hall sensor.  With the equation below from Ampere's Law you can calculate the magnetic field from a current source.  Assuming a distance of 0.5mm distance from the current source and 10mA current we would get 4uT.  This is too low for a hall sensor to measure.  You can improve this by creating a coil that would magnify the magnetic field.  You could also create a coil around a magnetic concentrator and force the magnetic flux to go through a hall sensor.  There is issues with this as you now create an inductor for the current you are trying to measure.  Another alternative is using one of our flux gate sensors.  These can measure lower magnetic fields but with this approach you would either have to gain up the magnetic field or shield external magnetic fields as well.  Just as reference the earths magnetic field is about 60uT.  Any other current near by will also create a magnetic field.  This is a lot of information so I can give you more information after you let me know what questions you have and what direction you are thinking of taking.

B = (µ₀ I)/(2πr)

µ₀ = 4π X 10^-7

 r = distance in m

I = Current in Amps

Hi Carlos,

This info you have shared is really helpful.

For Now I can add some more info for my requirement is current range, it's 10mA to 8A.

(Actual work - I have to consider machine is powered-off if current is less than or equal to 20mA
And powered-on if it's greater than 20mA.)

It'll take some more time for me to decide circuitry design.
Meanwhile If you suggest me for a product which will fit into this current range/requirement, will be helpful.

Thanks & Regards,
Hardik

Hardik,

I have a more follow up questions.  What is the reason you require magnetic solution?  Would a shunt based not work?  Is there a specific bandwidth required?  Higher bandwidth requirements would lean more toward the first option below.

Are you ok with using a magnetic core?  If so you may consider using the DRV421.  There is a magnetic core pictured in our DRV421EVM Users Guide and we have a TI Design (±15A Current Sensor using Closed-Loop Compensated Fluxgate Sensor Reference Design) that has another version a magnetic core.  The downside to this core is it would need to be designed for you application.  Depending on accuracy needed on the low side measurement (10mA) and external field around your measurement you may still need some magnetic shielding around the core.

If you cannot use a core you may need to use two components (DRV425 for low currents and DRV5053 for larger currents) with a flux concentrator.  There is an example of a flux concentrator in our TI Design, Contactless and Precise AC-Current Sensing Using a Hall Sensor.  It is somewhat a magnetic core as well but will not have some tradeoffs of what is used with the DRV421 device.  Like the other solution shield may be required.

Hi Carlos & Javier,

W.r.t the question asked by my colleague Hardik, I have some more doubts. What is the importance of bandwidth in Hall effect sensor?
Where and how should we consider it? Is it only for the noise part of the signal?

Please answer my questions

Thanks & Regards
Varatharaj A.

Hello Varatharaj,

The bandwidth of one of our hall sensors DRV5053 is 20kHz.  The DRV425 flux gate sensor is limited to 47kHz.  The DRV421 is limited by the core of the transformer and the output difference amplifier of 2MHz.  I am not sure of the frequency range you are looking to measure or if you would require higher bandwidth for transients involved.  If you use a magnetic concentrator the bandwidth could be limited by that as well. 

Noise could also be an issue if you are measuring very low magnetic fields using these magnetic sensor devices.  You may need to limit the bandwidth of your measurement.  I can assist if this a requirement once we find the correct path for your application.

Bandwidth is especially important when determining the range of signals to be measured.

At times it is desirable to detect very short duration events, for example when performing an isolated current measurement with a hall sensor or a fluxgate.

Take, as an example, a 1KHz PWM signal with a resolution of 8 bits. The requirement for either cycle by cycle or average current control with dictate the minimum bandwidth

• • At minimum duty cycle (1/256), the period is roughly 4uS, requiring a bandwidth of  256KHz.
  • At 50% duty cycle the period is half the PWM frequency, therefore requiring a bandwidth of only 2KHz

Other times, the opposite is true... For example, the measurement of the rotor speed on motors. In this case, slow, compared with the PWM frequency.

• In such situations the pulse rate is directly related to the rotor speed, say a 2 pole motor spinning at 9KRPM, or 150 rotations per second.
• Having a sensor with a lower bandwidth will ensure PWM noise is rejected, and the actual motor shaft speed signal goes trough

Depending on your application, the requirement for a higher bandwidth will also result in higher power consumption an vice-versa, which may not always be desirable or feasible.