increasing AC current

[Joe_Szalko]

HI everyone,

I currently trying to control a stepper motor with an NI USB-6211 DAQ device. While I can successfully create the signal I need in order to control the motor at any speed I want, I overlooked a simple spec of the USB-6211 which causes my setup to fail, it's lack of output current. The current I need for my motor is 1A but the output current that the DAQ gives is only 2mA, which means I need to increase the current by 500x to get the motor to actually move. I'm looking into emitter-follower diagrams because of thier current gain even though it has a voltage loss considering I have a excess voltage I can use, the DAQ range in +/- 10v I need +/- 3.2V. However, since I have little experience in circuits, I wanted to ask if this is the right way to go about the problem or if other ways would be easier.

any insight to my problem would be helpful, thanks

[johnsold]

Stepper motors are usually driven by switches, that is any given coil is fully on or fully off at a praticular time.

I suggest that you look at power MOSFETs or IGBTs.  Their inputs are like capacitors and do not draw any steady state current. You use a voltage to turn them on and off. The only current requirement is to charge the gate capacitance.  Look for devices rated at 3-5 A.

Or, since you seem to have little experience with power circuits, you might be better off with a stepper motor driver module.  You connect power and a signal to tell it direction and speed and the controller does the rest. The cost is probably less than the time, effort, and burned out parts you would have trying to do it yourself.

Lynn

[Joe_Szalko]

Lynn, 

just for clarification on your first comment. While Stepper motors can be driven by switches what actually drives them is an electrical power that charges the coils. the effect of this charge is usually dictated by which way the power is travelling through the coil, which is then usually controlled through switches. However, what you could also do wis flip the polarity of the power source itself to get the same effect by using an AC signal, which is what I'm trying to do. In my particular case my motor has two coils and is activated in a ++, -+, --, +- fashion at 3.2V, which can be described at two AC signals with 3.2V and operating at a 90 degree phase, where the freguency then controls the speed. Unfortunately my motor requires a power of 3.2 watts inorder to physically move the motor shaft, which would mean that I need 1A current in addition to my 3.2V to get my nessecary power needed. This helps explain what I physically see in my setup which is hearing the small clicks of the coils trying to move the motor shaft at speed that I dictate, but the motor shaft itself doen't move. I know this stuff because I previously tryed to control my motor through switches and while it did work the hardware limitations made my motor to slow for any real use.

thank you for your suggestions though, I will look into MOSFETs and IGBT's to see how I can use them for my purposes.