hall effect sensor/mosfet high current switch

[gt40]

After my prior attempts to build some magnetic ring switches, I finally got a combination that is working and doesn't have significant parasitic drain. Thanks to wquiles for suggesting the right hall effect sensor.



As he posted in my sst90 magnetic ring thread:


Quote:



This particular Hall Sensor consumes 10uA (that is micro-amps), so instead of a little bit over two months, it would take approximately 555 months to drain that cell. Of course, the cell will drain sooner by itself due to its own internal self-drain mechanism :naughty:



Here is the new sensor I got:

http://www.diodes.com/datasheets/AH182_AH183.pdf



I used this mosfet:

http://www.irf.com/product-info/data...rlr8743pbf.pdf

What was missing in my prior attempts was the pull up resister. All of the hall sensors I have found switch low when activated and by adding the resistor between the supply and output, it converts it to high which the mosfet needs to have to turn on.



This works with the mosfet turning fully on. I ran an sst90 at 10 amps with my bench power supply and no issues. The on off seems more repeatable than the reed switch i was using before and the positioning of the magnet is a bit less sensitive in that you don't have to get quite so close as the reed switch.



This circuit seems to work reliably and may be of use for anyone building a waterproof dive light as a means to switch it on and doesn't use reed switches. I have broken a few trying to install them as they are delicate and the hall sensor just works.



The final bonus is the components are really cheap:



$1.36 for the mosfet and $1.23 for the hall sensor and a few cents for the 10k pull up resistor. The bonus is the components are tiny too...

 

[gt40]

successful hall effect sensor/mosfet high current switch

After my prior attempts to build some magnetic ring switches, I finally got a combination that is working and doesn't have significant parasitic drain. Thanks to wquiles for suggesting the right hall effect sensor.



As he posted in my sst90 magnetic ring thread:


Quote:



This particular Hall Sensor consumes 10uA (that is micro-amps), so instead of a little bit over two months, it would take approximately 555 months to drain that cell. Of course, the cell will drain sooner by itself due to its own internal self-drain mechanism :naughty:



Here is the new sensor I got:

http://www.diodes.com/datasheets/AH182_AH183.pdf



I used this mosfet:

http://www.irf.com/product-info/data...rlr8743pbf.pdf

What was missing in my prior attempts was the pull up resister. All of the hall sensors I have found switch low when activated and by adding the resistor between the supply and output, it converts it to high which the mosfet needs to have to turn on.



This works with the mosfet turning fully on. I ran an sst90 at 10 amps with my bench power supply and no issues. The switch is reversed in that you put a magnet by it to have it turn off and take the magnet away to turn it on. I would like it ideally the opposite but this is working at least. The on off seems more repeatable than the reed switch i was using before and the positioning of the magnet is a bit less sensitive in that you don't have to get quite so close as the reed switch.



This circuit seems to work reliably and may be of use for anyone building a waterproof dive light as a means to switch it on and doesn't use reed switches. I have broken a few trying to install them as they are delicate and the hall sensor just works.



The final bonus is the components are really cheap:



$1.36 for the mosfet and $1.23 for the hall sensor and a few cents for the 10k pull up resistor. The bonus is the components are tiny too...

 

[Logman7585]

I'm creating a BLDC motor and I'd like your help. I've set the circuit as shown, except with a motor coil instead of an LED. When the magnet is near the hall sensor current flows to the MOSFET above the 2 volt gate threshold, but it isn't switching on or off, it just stays on. So instead of spinning, it just flips towards the coil. Any ideas?

 

[DIWdiver]

Wow, this is going to be a major hijack, but I can answer that. The problem is that the phase timing is off. You have to rotate the whole sensor array with respect to the magnetic poles so that as the rotor approaches one pole, that one gets turned off and the next one gets turned on. If you want equal performance in both directions, the sensors go halfway between the poles. If you want better performance one direction and can sacrifice performance in the other, you can adjust the timing one way or the other. If you're really clever and have the right electronics, you can even adjust the timing electronically and get even better performance in both directions.

IIRC, you have to have a different number of poles on the rotor and stator, so that you can tell it which direction to go. I believe the most common setup is 4 poles (2 north, 2 south) on the rotor, and 3 on the stator, though 2 and 3 might be common too. I'm not really an expert.

By the way, great family of sensors. I've used both the thru-hole and surface mount versions. I used the AH3212, which is very similar, for the magnet ring on my first dive light.
:twothumbs

 

[DIWdiver]

Looks like your light is direct drive (no driver is noted in the diagram), so you must be using a single LiIon cell. This should work okay for you, but if anyone else is thinking about using a driver with this circuit, the max supply voltage on the hall sensor is 5.5V, so for multi-cell batteries, you'll need a voltage regulator as well.

 

[Logman7585]

Wow, this is going to be a major hijack, but I can answer that. The problem is that the phase timing is off. You have to rotate the whole sensor array with respect to the magnetic poles so that as the rotor approaches one pole, that one gets turned off and the next one gets turned on. If you want equal performance in both directions, the sensors go halfway between the poles. If you want better performance one direction and can sacrifice performance in the other, you can adjust the timing one way or the other. If you're really clever and have the right electronics, you can even adjust the timing electronically and get even better performance in both directions.

IIRC, you have to have a different number of poles on the rotor and stator, so that you can tell it which direction to go. I believe the most common setup is 4 poles (2 north, 2 south) on the rotor, and 3 on the stator, though 2 and 3 might be common too. I'm not really an expert.

By the way, great family of sensors. I've used both the thru-hole and surface mount versions. I used the AH3212, which is very similar, for the magnet ring on my first dive light.
:twothumbs

I guess I can provide some more detail. I've attempted the setup with a darlington transistor and the same hall sensor and everything works great, the sensor switches current on and off and the proper time and the motor spins perfectly. The same setup connected to the MOSFET and the rotor wont spin, it just acts like an electromagnet. Without the pull-up resistor there is no current at all flowing. So that part is good. Now it just needs to switch the current. Obviously I'm missing something, but why does it work with one transistor and not the other?

 

[DIWdiver]

I guess I can provide some more detail. I've attempted the setup with a darlington transistor and the same hall sensor and everything works great, the sensor switches current on and off and the proper time and the motor spins perfectly. The same setup connected to the MOSFET and the rotor wont spin, it just acts like an electromagnet. Without the pull-up resistor there is no current at all flowing. So that part is good. Now it just needs to switch the current. Obviously I'm missing something, but why does it work with one transistor and not the other?

Well the most obvious answer is that the FET is wired wrong. Carefully check your pinout; gate goes where base was, drain goes where collector was, and source goes where emitter was. It sounds like you might have the source and drain reversed. That would definitely make the FET conduct all the time. Also, it's possible the FET has failed. The most common failure mode is to short, which would have the same effect.