I worked on a solenoid switcher design a few years back that needed fast response and I think we used Tranzorbs which are a bit like back to back zeners..... Just looked up the schematic. They were P6KE100CA. Obviously you'll need to use ones that suit your design. B On 25 Aug 2008, at 22:01, Picbits Sales wrote: > I've had a similar problem with some fast stepper motors. > > I ended up using some zener diodes as snubbers and it greatly > improved the > response time. > > I've noticed on a recent pair of scanners I've stripped they used the > ULN2003 on the stepper drive stage but put a zener in series with the > snubber pin on the ULN then fed this to +ve. > > HTH > > Dom > > ----- Original Message ----- > From: "Philip Pemberton" > To: "Microcontroller discussion list - Public." > Sent: Monday, August 25, 2008 9:20 PM > Subject: [EE]: Back-EMF catch diodes slowing solenoid response > > >> Hi, >> Well, I'm two days into my summer holiday, and I've already run out >> of >> things >> to do on my current projects. So I figured I'd resurrect an earlier >> project >> that I put on the backburner ages ago. >> >> A good few years ago, I bought a pair of Epson M-180 series impact >> printer >> mechanisms. These are basically 24-character dot-matrix printers >> which use >> five horizontal solenoids instead of the more typical single 9-pin >> vertical >> head. The idea being that it speeds up printing, and allows graphics >> printing >> where necessary. It's actually pretty speedy... for a 1980s vintage >> piece >> of >> kit. A lot more power hungry than my Seiko MTP-series thermal >> mechs, and a >> bit >> of a pig to design hardware around. Typical Epson kit really, fussy >> and >> finicky :) >> >> From my project notebook, I was having issues with the print head >> solenoids >> holding down for too long: >> >>> Print quality still terrible. P/Head solenoids seem to be holding >>> too >>> long, >>> 1N4001 diode snubber slowing decay. Removed diode - some >>> improvement, >>> but >>> ULN2003 driver failed in short order, probably due to back-emf. >>> Needs >>> further work. >> >> I've been digging through Horowitz & Hill, and scanning Google for >> about >> 40 >> minutes now, and haven't found any decent material on back-EMF >> suppression >> for >> transistors used for driving inductive components. I've found tons of >> references that boil down to "just use a 1N4001", a few that actually >> admit >> that a '4001 will slow a relay's switch-off response >> "significantly", but >> nothing on what to do to speed things up. >> >> Does anyone know of any good articles on this? I'd rather like to >> get the >> M180s doing something useful - maybe hook one up to a PIC and use >> it to >> grab >> screendumps and trace data from some of my testgear. >> >> Of course the easy answer is "give up and dig out a thermal printer >> module", >> but they're text only (7-pin head, not the 8-pin graphics head) and >> frankly >> it's far easier to get paper and ribbons for the Epson modules than >> it is >> to >> get 4" wide thermal paper for the MTPs... >> >> Thanks, >> -- >> Phil. >> piclist@philpem.me.uk >> http://www.philpem.me.uk/ >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >> >> No virus found in this incoming message. >> Checked by AVG - http://www.avg.com >> Version: 8.0.138 / Virus Database: 270.6.7/1632 - Release Date: >> 25/08/2008 >> 07:05 >> >> >> > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist