Snubbers are a bit of an art form. Ideally, the R should be chosen in accordance with the ringing frequency & the inductance in order to reduce the Q to 1. In practice, most of the stray capacitance etc is distributed and an exact mathamatical solution can be virtually impossible. In most cases I just measure the ringing frequency on a 'scope. Then calculate the peroid (1/frequency) and then calculate an RC product to match this period. R is normally in the 100-300 ohm area as a starting point. C = period/R. If there is still significant overshoot, then reduce R & increase C. If the resistor gets hot, then either increase the value & decrease C or increase the power rating. Play around with the values a bit until you get a waveform that looks OK. Not very scientific but it does seem to work - until the relay is changed to a newer model or a different manufacturers "equivalent". Richard P brusque@hotpo p.com To: "Microcontroller discussion list - Public." Sent by: cc: piclist-bounc Subject: Re: [EE] Snubber calculation es@mit.edu 31/03/05 04:05 Please respond to "Microcontrol ler discussion list - Public." Hello, thanks Bob et all for your kind comments and sugestions. I'll make some more tests when on the facility and tell my report to you. Now, returning to the original topic... someone knows how to calculate a snubber? Best regards, Brusque -- --------------------------------------------------------------------- Edson Brusque C.I.Tronics Lighting Designers Ltda Research and Development Joinville - SC - Brazil http://www.ryan.com.br/netiqueta.htm www.citronics.com.br --------------------------------------------------------------------- -- 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