adamziegler

Yes, you are right it is a huge waste of power, which is probably why most modern drivers use a current chopper. Could you list a couple, so that I could look into them a bit more? I have, but used a very different method. I had some low power transistors that I attempted to match and stack. The transistors acted as the switch, and with the base resistor I controlled the collector emitter current. Stepper stays cool under load, and is capable of moving significantly faster. Problem is, those transistors were not dissipating power while standing still. I actually liked this method, except since hFE was different for each group of transistors, I needed to use different resistor arrangements for each phase of the stepper. I wouldn't mind perusing this method of current control... it greatly reduces the number of components... I am just having problems finding a power transistor that I can drive with 20mA... and get CE current of 1.5A. Any thoughts on this approach? so something like a TIP120? http://www.st.com/stonline/books/pdf/docs/4128.pdf

Thank you audioguru... I appreciate the time you are taking to help me along. Yes, this makes sense to me. But.. to make sure we are on the same page... a stepper coil supplied directly with 6V and 1.5A reacts slower than a stepper plus resistor (or current sink) supplied with more Voltage that has been current limited to 1.5A. I assume you are recommending PWM here? (If not what did you mean?) As of right now I do not have the ability to do PWM with my setup. I would like to look at PWM in the future, but I am content to have a space heater for a driver at the moment ;D I am fairly certain that this 150 oz-inch stepper can be driven with a higher voltage source as long as the current is limited to 1.5A (in fact it is recommended). However on my last schematic I had lowered the voltage to 12V. I take it this means I need to search for a power transistor that has a lower current gain at 1.5A? Again, I really do appreciate you help. :)

Ok thank you, I will get rid of the zener and add in a regular diode. IIRC... that will give me about 0.65V a peice... so say I use 1.. I need a 0.4 or 0.5 ohm R4. If I use two diodes (3 total now) I have R4 at 0.9 Ohms... and so on. So any advice on sizing R3 and power rating the components? You had mentioned before that it is good for low currents, but went on to talk about my currents. Will this work for me? Low current gain.. so hFE < 70 ?

Alright... lets try this: Found out my stepper voltage rating... can be safely ignored... the 1.5A is what cant be exceeded. My power source is a 140W ATX. I have added a constant current source to each coil. If I make D3 a 2V Zener... that means R4 should be ~1.3Ohms ... which will limit the phase to 1.5A. Is that accurate? How do I estimate R3? For power issues R3... 5W adequate? Could I get some help sizing the other components for power?

audioguru, thank you for the reply

Anyone? Any ideas? Do I need to supply more information?

This is a quick attempt at a diode/transistor based current source. Again... dunno if this is right... but I think my load is in the right place this time. I think I would have to use a PNP for it to be correct on the other schematic.

Hello everyone... it looks like you all have a great forum here! Brief introduction... I have some basic experience with electronics. My problem is I have been out of it for a number of years, and most of the basic concepts that had to come easy to me, have been forgotten about. A few days ago I set off attempting to design a simple stepper circuit primarily to help my self re-learn some basic electronics skills. The re-learning curve has been very steep for me. So treat me like I am a newb because at this point... I am! ;) Project background... I have a computer program (EMC... if people are interested, I can talk a bit more about it) that has a built in pulse generator which can be assigned to the pins of my parallel port. I plan to feed the signal the signal through an photocoupler, and which will then trigger some mosfets which in turn power a combination of phases in the stepper. I have manged to make a test circuit to set the software setup and general circuit idea, and it seems to work pretty good. I am now attempting to refine the circuit for real use. This is what I have so far: For starters... any general comments on this? Notice the power resistors (R1).... I started with those because V=IR is a concept I remember. Problem is, its not the most efficient way to control current. Today I started looking at using some bipolar transistors at providing a constant current source.... its a slightly better option for driving a phase of the stepper. This is where I have started to run into some major hurdles. I started with this: Will this work? Is my device in the right place? I need some help choosing components. I thought there was a way to to this with some diodes and 1 transistor, but I cannot remember. Again... this is primarily a learning experience for myself. I welcome questions comments and criticisms! Thank you.