Do you guys have actual test data showing improved life with the zener or tvs instead of a simple diode? Every relay I've seen which had an integrated diode used a simple switching diode. Also, usually the current required to keep the relay closed is only a tiny fraction of that required to make it close so only a small portion of the coil current decay is relevant to the actual speed at which the contacts open. On top of that, usually relays are designed so that the magnetic circuit is broken before the electrical circuit - and once the magnetic circuit starts to open there is a positive feedback effect which causes the attractive force to drop very rapidly. In sum, I would be very surprised if the type of diode made much difference to the contact life, except for reed relays. I thought that the usual reason for wanting the field to collapse faster was to make the delay from open signal to actual open circuit shorter for system reasons. On Dec 18, 2017 2:36 PM, "Spehro Pefhany" wrote: > > The diode across the coil method isn't the best either, if you care how quickly the relay opens. > Slow opening can result in contact welding. > > The best method is a Zener from Collector/Drain to ground. Set the Zener voltage a bit below the transistor VCE/VDS rating. > This speeds up the collapse of the current in the coil by as much as 3x Dave is right, this will help get rated life out of the relays. They are *not* rated with diodes directly across the coils. You may be able to use one TVS or Zener (total) and one diode per relay. Spehro Pefhany > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .