On 3/22/07, Vasile Surducan wrote: > On 3/22/07, John Dammeyer wrote: > > Hi Orin, > > > > > > > > On 3/21/07, Vasile Surducan wrote: > > > > Based on drawing ES-I is input and E_O is output and here the > > > > protection could be OK. > > > > Orin, a stabilizer circuit (even the three terminal one) has a > > > > negative feedback, so the voltage can't grow to 11.4V even in bad > > > > dreams. If the supply is based on a three terminal stabilizer the > > > > reverse diode between Vin and Vout will become on and the spike will > > > > be absorbed in the filtering cell. > > > > > > Well, that all depends on Vin to the regulator which is undefined... > > > as you note, the supply schematics aren't given. > > > > > > Then the problem being protected against was a short to 12V, not just > > > a spike. What if Vin to the regulator is the same 12V? > > > > > > Orin. > > > > It's currently a 7805 regulator. > > We are splitting here the wire in four for a simple power supply problem. > Unfortunately I've falled in your game... > > If the current is limited on the PIC IO through a simple serial > resistor (and nothing else) would be just fine. Because the output of > the 7805 will never be 12V. With enough series resistance, the PIC will survive - but may not work while the short is present. Which in this case is fine. No quibbling there. The problem case was the diode to VCC with no series resistance, which even the original author said might trash the diode. We did just have another thread that concluded that using the series diodes put you outside the spec for input pins and was right on the absolute max ratings. Orin. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist