Hi Justin, I'd be tempted to keep some sort of protection(*) just in case. Note that as the relay drops out, it's inductance will change. (Probably reduce). This may happen fairly quickly regardless of the rate of decay of the current as it's mechanically based. So there is the possibility of some sort of voltage spike regardless. The body diode of the MOSFET won't provide too much in the way of protection on its own although you may be able to find the avalanche limits for it - might be OK if the current is small enough. *Protection could be :- 1. MOV or Diode across coil. 2. MOV or Zener D-S across switching fet. 3. smaller (power wise) zener D-G on switching fet. (?). 4. Resistor across coil. 5. other? RP On 31 December 2016 at 22:13, Justin Richards wrote: > I have a working circuit that delays the off time of a relay. > > It simply has a 10uF in parallel with 3.3M ohm that is tied between the > Gate and Source of a BS170. The cap keeps the Gate voltage high and slow= ly > discharges. > > In the original design I had a protection diode across the relay coil. > > But I need to make changes and space is limited and was thinking the diod= e > can go. > > The rationale is that the coil never suddenly turns off so no inductive > spike. The current gradually decays as the cap discharges over a 1.5 min > period. > > The data sheet also shows a body diode for the BS170. > > So what say ye, is there any argument for keeping the diode in this case. > > Cheers Justin > -- > 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 .