how to conect an hall sensor to npn trans to a mosfet n ch? 12 v supply ?

MaxHeadRoom

Joined Jul 18, 2013
23,786
That device shows as a legacy product now.
Take as 10k resistor to +ve from the sensor output pin and feed output into a mosfet gate.
That is a logic level Mosfet which you don't necessarily need for 12v supply.
Max.
 

Reloadron

Joined Jan 15, 2015
6,128
The A3144 Allegro Hall Effect Sensor is an open collector NPN output.
A3144 Hall Effect.png
Do as Max suggested and use an external 10K Ohm resistor between the output pin and +V. Use that to drive your logic level MOSFET gate. You don't need the 2N2222.

Ron
 

Thread Starter

Erick npn

Joined Sep 25, 2017
13
Unless you're using it to invert the logic - could be useful for that. If you want Hall output low to mean MOSFET active and vice versa, then use the NPN. Otherwise I'm with Max and Ron.
That device shows as a legacy product now.
Take as 10k resistor to +ve from the sensor output pin and feed output into a mosfet gate.
That is a logic level Mosfet which you don't necessarily need for 12v supply.
Max.
Hi everyone and thanks for the suggestions. this circuit is supposed to drive one or 2 coils as electromagnets, in short it's a dc motor control. My concern it's about the resistors that I should use between those components. I'll upload the circuit so you will have a better understanding.
 

Thread Starter

Erick npn

Joined Sep 25, 2017
13
IMG_5693.JPG I made the eletromagnet therefore I don't know the specification. I'm aware that the cosciotto has to comply with the load in this case the coil, any idea how can I calculate it? Thanks
 

Thread Starter

Erick npn

Joined Sep 25, 2017
13
Hi, all is connected but I don't get too much power to the eletromagnet as when I conect it directly to the battery... anybody knows what I may do to have more power? May a condenser? Thanks
 

ebeowulf17

Joined Aug 12, 2014
3,282
Those connections aren't setup the way you want. You've got R2 (560k) in series with the supply voltage to the electromagnet. That would only allow 0.02mA through the electromagnet. I'm not sure how much current you'll need through it, but it's bound to be more than that.

You also don't have any switching control the way you have things wired up - your MOSFET has a constant ground connection, a constant 560k ohm connection to the 12V supply, and a connection to the coil. It's not being controlled by the hall effect sensor in any way.

Assuming you need the NPN transistor in the middle (which still isn't clear because we don't know if you want the logic inversion it provides,) this image I found online is pretty close to what you'd need:
IMG_2871.PNG
In place of the output pin, you'd connect the output of your hall effect sensor, with a 10k pull up resistor connected from that output to the supply voltage as Max and Ron described earlier. You may also need a resistor in series with your coil, depending on the nature of the coil, but it almost certainly shouldn't be anywhere near 560k! Even just 1k would get you down below 12mA of current.

We need to know more about what current you need through the coil and which hall effect state should correspond with which coil state (logic inversion needed or not) in order to provide more helpful information.
 

Thread Starter

Erick npn

Joined Sep 25, 2017
13
Thanks for the suggestion, I don't know too much about electronic, the example I followed were based on 5 V power supply... that's the way I use that resistor to do not blow up anything lol! Basically I don't need a resistor between the supply and the npn transistor, it's this correct? And what about the mosfet? You mentioned something about a constant ground, how should I conect it? Thanks for your patience!!!!
 

ebeowulf17

Joined Aug 12, 2014
3,282
Sorry I don't have time to get on the computer and do a custom schematic for you, but the schematic in my last post is 90% of what you need. The only additions beyond what that shows are:
  • a pull up resistor (maybe 10k?) from the hall effect output to the supply voltage (your 12V, or maybe 5V if that's what you're r testing with first.)
  • Maybe a resistor in series with your coil, depending on the resistance the coil already has, and on how much current you want.
If you haven't already, you'll need to read the datasheet for each device and make sure you know which pin is which.

As to your question about the resistor before the NPN, you can see in the schematic I shared that you actually need more than one resistor on the NPN
 

Thread Starter

Erick npn

Joined Sep 25, 2017
13
Thanks for the help, the circuit as it is works I have it on a breadboard. And it's pulsing at the right time. few things doesn't make sense according to the data sheet of those components that's the way I was asking some help. I'll try with the circuit you advised me to see the difference. Thanks anyway
 

Thread Starter

Erick npn

Joined Sep 25, 2017
13
Probably the circuit I made on paper sucks! Lol this is the working one! The resistor are the same as the one I gave early. If I can do anything to improve it, will be good!
 

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ebeowulf17

Joined Aug 12, 2014
3,282
Probably the circuit I made on paper sucks! Lol this is the working one! The resistor are the same as the one I gave early. If I can do anything to improve it, will be good!
Cool. I sort of enjoy reverse engineering circuits and creating schematics, so I'll see if I can do that here.

Once we have a clear schematic, it'll be easier for other forum members to help troubleshoot any issues with the circuit.
 

ebeowulf17

Joined Aug 12, 2014
3,282
Well, here's my first attempt - drawing as I was reading the circuit off the breadboard. Didn't leave myself enough space to put the motor over the MOSFET. If I had more time, I'd redraw it, but this should at least make it readable for the other members.

My first impression is that the 100 ohm resistor isn't needed at all, because the 10k is already limiting current through the base of the NPN. I also wonder if the 10k might be too high, as it's limiting current through the base an awful lot.

I don't have time right now to dig deeper into the specs and see if my gut feelings are right, so hopefully someone else can help make sense of this. What I've shared so far are just impressions and guesses!

IMG_2877.JPG
 

ebeowulf17

Joined Aug 12, 2014
3,282
Hi, all is connected but I don't get too much power to the eletromagnet as when I conect it directly to the battery... anybody knows what I may do to have more power? May a condenser? Thanks
Can you measure the voltage (relative to ground) at the MOSFET gate and also across the motor when the motor is running?

Despite some resistor selections that aren't what I'd expect, it looks to me like your circuit should work. The voltage measurements might help reveal what's not working.
 
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