# Hall Sensor - Limit Voltage

Discussion in 'Sensors and Actuators' started by smanuk, Nov 7, 2012.

1. ### smanuk

1
0
Nov 7, 2012
Hi All, I am hoping someone can help me with this.

I have a Hall effect sensor and supply 6 volts to it of which I cannot change. The sensors range is between 0.5v when the magnet is placed away from it and 6v when a magnet is placed near it. So if works as a potentiometer but no moving parts.

I want to be able to limit the voltage given from it to just 1.5v. What components would I need to put after it in order to limit the voltage from 6v to 1.5v anything below the 1.5 cannot be reduced (it still needs to show 0.5v - 1.5v exactly the same as before) so I effectively need to somehow limit it.

I thought about a voltage regulator circuit but figured this would affect voltage being linear from 0.5v to 1.5 ....

If I reduce the 6v incoming voltage I no longer get the 0.5 that is required so that is not an option.

David.

2. ### Laplace

1,252
184
Apr 4, 2010
You could use a voltage clamp on the sensor output. Several diodes in series and forward biased to ground will keep the sensor voltage from rising beyond the forward voltage of the diodes. For more accuracy try an adjustable bandgap shunt regulator diode such as the LM385. Another possibility would be to use the 6-volt power supply with a rail-to-rail operational amplifier. Amplify the sensor voltage by a factor of 4; the 1.5 volt will max out the range at 6 volts. Then divide the signal by a factor of 4 to recover the 0 to 1.5 volt range.

3. ### TedA

156
16
Sep 26, 2011
David,

Is it possible to tell us the make and model of your sensor, and something about the device or circuit it is to be driving? Can you provide links to device data sheets, and circuit schematics? A general description of what you are doing would not be a bad idea.

It is not clear if the 0.5V to 1.5 output you need should reach 1.5V at the same magnet position that it does now, or when the magnet is positioned where you now get the 6V output. Laplace assumed the former.

How exact must the 1.5V limit be, and how close to the limit must linearity be preserved?

What are the impedances involved. Can the output of the sensor be clamped without excessive current?

What is the input impedance of the circuit the sensor is driving?

How precise and stable must the system be?

Do you plan to make one, or a million, of these?

How expensive can the solution get?

Ted