Kirk Wallace wrote: > > The IA and IB sink the LED's on two optocoupler inputs each. The high > side of the LED's is driven by the Q and /Q quadrature signals. I am > guessing this forms a NAND function or an Inhibit? I wonder if the > inhibits are needed to prevent shoot-through? If that is the case I will > need to be very careful not to allow shoot-through. Here are some > pictures of one of the drives. > > http://www.wallacecompany.com/machine_shop/Shizuoka/00001-1a.jpg > http://www.wallacecompany.com/machine_shop/Shizuoka/00002-1a.jpg > > I am wondering if this is just a simple H-bridge with current limit? If > anyone has more information on this drive, I would appreciate hearing > it. >
It seems to have a LOT of parts for an H-bridge, and you mentioned before "common" wires on the motors. So, it sounds like a very typical current-limiting unipolar drive. It would need 4 transistors for the unipolar phases, and then more stuff for the current regulator(s). I see 4 copies of some circuitry at the bottom of your first picture, so I'm guessing the bottom 4 transistors are those phase drivers. There are 7 big diodes, too. I can't quite explain the whole topology from the pics, but a dual H-bridge would not use the motor center taps, and would need 8 identical power transistors. You have 6 identical TO-218 units, and 2 TO-220s and one more (different) TO-218. Yes, it seems reasonable they need to turn off one transistor before turning on the opposing one. It wouldn't actually cause "shoot through", but an equally rough situation due to the center-tapped transformer action of the motor winding. If those transistors are Darlingtons (quite likely) then they can take a LONG time to turn off, in the several microseconds range. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
