Post by thread:[EE]: Step motor controllers

> >David, there is little to be gained by using chopping >with such a low supply voltage. What voltage and current >motors are you using? Maybe if you explain more you >might get more responses on this one? :o) >-Roman It's a 5 ohm motor, bipolar windings, running from a 6-8.5V supply. The motor wants 0.5A. I don't want to spend any more power than I must in driving it, since this is a battery operated application. -- Dave's Engineering Page: http://www.dvanhorn.org Got a need to read Bar codes? http://www.barcodechip.com Bi-directional read of UPC-A, UPC-E, EAN-8, EAN-13, JAN, and Bookland, with two or five digit supplemental codes, in an 8 pin chip, with NO external parts. -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

> It's a 5 ohm motor, bipolar windings, running from a 6-8.5V supply. > The motor wants 0.5A. I don't want to spend any more power than I must > in driving it, since this is a battery operated application. You can't afford the losses of a darlington output device so your best solution is probably to go semi-discrete with N-ch/P-ch half bridge drivers or perhaps a low voltage DC motor driver device. Then add your own current sense/chopper circuit. I'd be tempted to have a play with MOS output controller IC's you've already dismissed because of the minimum motor voltage. AFAICT, the minimum would be dictated by the ability of the charge pump to get a high enough Vgs on the top FET to turn it hard on. I would expect that with a 6V supply you're going to be close enough that even if the Rds on is twice what it is capable of, you are still on the winning side. Try it. If it works OK for your needs, flick an email to the chip supplier and ask for their opinion. Steve. ====================================================== Steve Baldwin Electronic Product Design TLA Microsystems Ltd Microcontroller Specialists PO Box 15-680, New Lynn http://www.tla.co.nz Auckland, New Zealand ph +64 9 820-2221 email: .....stevebKILLspam@spam@tla.co.nz fax +64 9 820-1929 ====================================================== -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestKILLspammitvma.mit.edu

On Mon, 17 Dec 2001, David VanHorn wrote: > > It's a 5 ohm motor, bipolar windings, running from a 6-8.5V supply. > The motor wants 0.5A. > I don't want to spend any more power than I must in driving it, since this > is a battery operated application. > -- I say a bridge half with bipolars, half with MOS will be the better choice. But I don't see why not 3717, 3770 ; 8.5V x 0.5 = 4.25VA 10V x 0.5 = 5VA No big difference but easy way. Vasile -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 01:03 PM 12/19/01 +0200, Vasile Surducan wrote: >On Mon, 17 Dec 2001, David VanHorn wrote: > > > > > It's a 5 ohm motor, bipolar windings, running from a 6-8.5V supply. > > The motor wants 0.5A. > > I don't want to spend any more power than I must in driving it, since this > > is a battery operated application. > > -- > I say a bridge half with bipolars, half with MOS will be the better >choice. But I don't see why not 3717, 3770 ; 8.5V x 0.5 = 4.25VA >10V x 0.5 = 5VA >No big difference but easy way. >Vasile Their spec says minimum motor voltage of 10V. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> On Mon, 17 Dec 2001, David VanHorn wrote: > > > > > It's a 5 ohm motor, bipolar windings, running from a 6-8.5V supply. > > The motor wants 0.5A. > > I don't want to spend any more power than I must in driving it, since this > > is a battery operated application. Sounds like a small 17 frame or pancake stepper, 2.5v 0.5A. You are unlikely to get better than 2:1 with any chopper IC so it will probably cost you 200mA+ from the battery anyway. Unless you need high speeds, I think the best solution is to switch to a 12v 200mA motor, these still have decent speeds and torques at 6v, and being unipolar you only need 4 tiny fets to drive the motor, you can use low sat fets as you only need 4 and the circuit is simple enough to wire. Another good point about the higher inductance 12v motor is that you can implement simple slow pwm from the pic outputs, good for low power "hold" modes and stuff. Now you will probably tell me you have to use the 2.5v motor? ;o) -Roman -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics