On Friday 31 October 2014 12:53:28 Kirk Wallace did opine And Gene did reply: > In case anyone might be interested, I mentioned on IRC some issues I > had with a blown out unipolar drive: > > http://www.wallacecompany.com/machine_shop/Shizuoka/00001-1a.jpg > > http://www.wallacecompany.com/machine_shop/Shizuoka/Bandit_Stepper_Driv > er.png > > http://www.wallacecompany.com/machine_shop/Shizuoka/Shiz_TIP36-1a.jpg > (Darlington = two xstrs on one mini pcb, TIP36C PNP pair on high side > for PWM current control on AA and BB, TIP35C NPN pair on low side for > motor coil stepping on A1, A2, B1, and B2) > > I got the last of the parts yesterday and installed them to the Y drive > and it works fine now. Unfortunately, the Z drive went out while > testing. This time I knew what to look for and had spares, so I > repaired the Z drive in short order. I hope there isn't another issue > causing these drives to go out. It seems that a transistor shorts out, > taking the other high or low side transistor out, then the fuse. On > the other hand, if there was an overload from the motor, I suspect > just the fuse would blow. (BTW, TIP35/6 = 25A, Fuse = 12A Fast Blow) > > In looking at how Darlington transistors work, I'm surprised that two > of the same transistors are used for the first and second stage (hFE = > 1600). I suppose transistors are cheap enough that there are no > savings in using a smaller transistor for the first stage. If another > transistor blows out, I may try a modern single module Darlington like > these: > http://www.digikey.com/product-detail/en/2SD2083/2SD2083-ND/3661817 > http://www.digikey.com/product-detail/en/2SB1383/2SB1383-ND/3929429 > (hFE = 2000, one high side, one low side) > > Although, I really don't want to put much more effort into these old > drives. Plus the circuit traces are pulling up when I remove the old > parts. That could be an SOA failure, where a bug spends too much time in the transition between on and off and punches thru.
TBT, most darlingtons are too slow, particularly for power drivers, to be suitable for such usage, and I would expect a relatively high failure rate. Servo, or steppers? Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
