I have not followed this thread, but typically the switching speed of the = diode needs to be faster than the transient. Fast schottky diodes are = typically used. There are special diodes that are designed for the purpose= . = Rectifier diodes like the 1N4007 will not switch fast enough to be effectiv= e = as a transient sink for fast transients. The 1N4148 (also 1N914) are faste= r = and will turn on with a fast transient because they have a faster switching = speed. The 1N4148 is trying to do the job but apparently it cannot handle = the transient current. The 1N4007 is probably not even responding until th= e = transient cycle has ended or is near the end. An O-scope is not an ideal = device for transient analysis. A spectrum analyzer is the more appropriate = tool. But not everyone has one., so an O-scope may be all you can use. You = might pick out a schottky diode to swamp the relay coil. Also, it depends = on how you make the field rise. The faster it rises, the higher wider the = spectrum of the transient. If you turn the rely on hard, you can generate = an induction kick of 1 or greater KV. If you turn it on slower you can = minimize the transient. A lot ( actually everything) depends on your = application. The application spec is the starting place. Look at your = timing diagrams and see what you need to do. I hope this helps a little. = Sometimes a small capacitor across the diode will help. But remember that = the relay will not turn on or off until the capacitor is charged or = discharged. Your application spec will tell you if this is an option. Rich :-) ----- Original Message ----- = From: "Enrico Schuerrer" To: "Microcontroller discussion list - Public." Sent: Monday, February 06, 2006 5:06 PM Subject: Re: [EE] Transient Suppression - was Re: [ee] 3904 base resistor -----Urspr=FCngliche Nachricht----- = Von: "Richard Prosser" An: "Microcontroller discussion list - Public." Gesendet: Montag, 06. Februar 2006 20:21 Betreff: Re: [EE] Transient Suppression - was Re: [ee] 3904 base resistor > But the flyback voltage generated by the relay coil turns the diode > on. The voltage rating of the diode only needs to match the power > supply requirement (the voltage accros the relay when on) - plus the > usual margin. And why 1N4148s are dying, 1N4007 not? Enrico -- = 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