-----Urspr=FCngliche Nachricht----- = Von: "Spehro Pefhany" An: "Microcontroller discussion list - Public." Gesendet: Mittwoch, 08. Februar 2006 14:31 Betreff: RE: [EE] Transient Suppression - was Re: [ee] 3904 base resistor > At 09:46 AM 2/8/2006 +0100, you wrote: > > > > Sideline: does a diode spec mention a maximum *forward* voltage? > > > > The forward recovery time of a slow-as-molasses diode such as the 1N4005 = is > a couple hundred ns at 100mA typically. So, the voltage might overshoot a > a volt or less with a typical edge from an inductor. No big deal. > 1N4006,7 use a different die and are about 50% slower. Reverse recovery of > these slugs is in the microseconds. > = > On the 1N4148, with 50mA switched, 20ns rise time, you'll see less than 2= .5V > forward peak forward voltage (maximum guaranteed). > = Yesterday I tested a simple relay switch first with a NPN switching transis= tor (2N2222) and then with a MOSFet. The relay was a 2 contact 12V/200 Ohms= printed board relay made by Schrack and I tested different diodes. Conclusion for me: the quick FET produces the biggest spike, independent fr= om the diode. The voltage runs for nearly 1 =B5s up to 160 Volts, measured = with an good old analog Tektronix 300 MHz scope. The best diode for suppres= sion was a BYV2100, a Schottky soft recovery diode (a little bit expensive = as a diode for a relay), the second best a 1N4148. At this diode the spike = was nearly 80 Volts high, so with an other relay maybe the diode will come = in trouble... (80V / 200 Ohm =3D 0,4 A !). = The lowest spikes I measured with the NPN-transistor switching the relay, e= specially when I put 330pF between base and ground (22 Volts spike). Regards Enrico = = -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist