How do I control the speed of a 24 volt DC motor with a 5 volt signal?

[paudi]

Hi guys, I need your expertise here. I am trying to control the speed of a 24 volt dc motor for a project. To do this I am using a MOSFET transistor. I am using the 5 volt output from a NI myDAQ microcontroller. When I connect up the circuit, the MOSFET allows roughly 13 volts to pass through the motor without a gate signal. When I apply a 5 volt signal to the gate of the MOSFET transistor it sends 24 volts to the motor and remains at this even when the 5 volt signal is removed. My plan was to use PWM on the gate signal to control the speed of the motor. I was hoping that the motor would be at 0 volts and ramp up to 24 volts with a 5 volt gate signal. It is a 3.6 amp motor and the MOSFET is a IRF520.

http://pdf1.alldatasheet.com/datasheet-pdf/view/22389/STMICROELECTRONICS/IRF520.html

http://www.ebay.ie/itm/Brushless-DC24V-Magnetic-Drive-Pump-640GPH-Motor-Speed-Variable-0-100-50C-246...

http://www.electronics-tutorials.ws/io/io_7.html

For the last link the circuit I am using is the Unipolar transistor switch circuit.

Any more info needed I will be glad to supply. Thanks

[Highland_Controls]

Do you have any instructions for that pump?  Why not just use the analog out from the MyDAQ and use the 0-5V control mode?  Are you bypassing the controller box when you are trying the PWM?  I think you need their controller, and from what I can tell, you must supply 24VDC and then use a separate control signal.

[Garrett9]

I am unsure what the pump is for but I can help you to control the speed of a single phase brushed 24V DC motor.  I would recommend using an amplifier that can handle a pwm signal.  It will take a PWM from your myDAQ and translate that to a analog voltage to your motor.  This analog voltage will be supplied by your external 24 VDC Power supply.  A good example of this type of amplifier can be found here:

http://www.robotmarketplace.com/products/0-SMPH.html

Hope this helps