I am pretty new at all of this. Still don't have my head around it all. I want to use a Transistor to turn a DC motor on and off. Really simple... Nothing special. Motor can draw a decent amount of current (say about 10 amps when stalled, 1.2 amps while running). I will control this with a Micro controller (Arduino). So my question is simple - can I use this Transistor to do it? (MJ300, http://www.farnell.com/datasheets/89477.pdf)

Can a micro controller turn this transistor on directly? (40 ma max per IO pin) Or do I need another transistor in there somewhere? Also - if I controlled the Base with a 12 volt source - will I blow it up? (I suspect yes) Thanks,
Brandon

 

Don't forget a diode across the motor to protect the transistor.

I give this schematic only by way of example, other than the diode it doesn't apply...

There are types of transistors that have much higher gain, which is what you need. You can buy Darlington Pairs that are prepackaged.
Think TIP100/TIP101/TIP102.

 

A MOSFET will dissipate less power when it is fully turned on because it drops less voltage (Vds) than a BJT (Vce).

 

OK - how about something like this?

http://www.fairchildsemi.com/ds/ND/NDB6060L.pdf

That says it uses logic level input - so I think I can use this directly from my micro controller?

 

I have a bunch of these laying around - FQP17P10

Can someone help with a really simple circuit design to help my power a motor? I have 5 volt 40 ma output directly from my micro controller - I also have 12 volt 1 amp output from another section of the board (controlled also by my micro controller). I think with this particular MOSFET I would need to use the 12 volt output...?
Thanks for all the help,
Brandon

 

Yes, it will work.
Note, that you need to connect a 125 ohm resistor between the output of the uC and the MOS gate. Also, connect a 10K resistor between the gate and the source of the MOS.

The motor has to be connected between the drain and 12V and with a diode in parallel with it as to absorb back EMF. The diodes cathode has to be connected to 12V.

Note that, if you want to decrease the switching time you can use a BJT or a MOSFET driver IC to drive the MOSFET's gate.

Another suggestion, to protect the uC in case the protection diode fails, is to use an opto-coupler to drive the MOS.

 

Have you had any experience programming the Ardiuno board to generate a PWM output signal?

hgmjr

 

I have been able to use PWM on the arduino powering a LMD18200T but I get almost NO torque out of the motors. I have NO idea why - so. Also the LMD18200T can only drive 3 amps. Which may be enough... but the real problem for me is that even with a high PWM freaquency (~32kHz) I can't get enough torque from the motor. I *THINK* it is because when the PWM signal is LOW the LMD18200T is 'breaking' the motor. If I could get this to work I would be in good shape too.

 

Post your circuit to make sure it is correct.

 

Once we have the schematic we can probably help you out.

hgmjr

 

I will put something together to post. I just got a MOSFET I had laying around and tried this. It seems to work (thanks mik3 for the MOSFET suggestion). My intention at this point is to pulse the signal to the MOSFET to get about 9 volts from my 12 volt supply. Hopefully I don't run in to the same problem I had with the LMD 18200T.

 

The LMD 18200T is an H bridge MOSFET driver, it cannot drive motors directly. Its job is two drive the MOSFETs which control the motor.

 

Sorry for this terribly simple schematic - not very good with Eagle yet.

I have 3-4 EN at +5 from one of the IO pins on the Arduino. Input 4A I plan to PWM with 75% duty cylce. That SHOULD give me 9 volts to the output 4Y. I *HOPE* that this will give me enough power on my motor. The FQP50N06L says it already has a protection diode in it. The big question for me is - Can I PWM the power to the FQP50N06L? I assume yes?

 

http://picasaweb.google.com/lh/photo/-La-dXNWPAskr9LZL0Un_Q?feat=directlink

 

Here is a circuit of how to connect the L293:

http://www.me.umn.edu/courses/me2011/robot/technotes/L293/L293.html

Your connections are wrong.


What is more, side 2 of the motor has to be connected to 12V and not ground.

Also, you need the protective diode across the motor regardless if the MOS has a built in diode.

 

I assume though that I CAN PWM the input to the MOS?

 

I assume though that I CAN PWM the input to the MOS?

If you build the circuit correctly you can PWM the MOS and control the motor.

 

The diode protects the transistor, any transistor. If the motor runs without it there is a chance the transistor will come away damaged.