Guest liquibyte Posted August 31, 2014 Report Share Posted August 31, 2014 Sorry, I made a mistake converting the original schematic to the fixed and improved one.You do not want the negative supply pin 4 of U2 to be negative -1.3V because then U2 will have its total supply voltage very close to its maximum rating of 44V (+42.6V plus -1.3V= 43.9V).U2 does not need a negative supply so connect its pin 4 and R10 to the 0V from the unregulated power source.Most little NPN silicon transistors have avalanche breakdown (like a zener diode) of their base-emitter junction when it is reverse biased more than about 6V so maybe you have the emitter and collector pins of Q1 reversed?Here is my corrected schematic:Moved pin 4 of U2 and R10 back to the original locations and we're good. You were right about the transistor being in backwards. I think the datasheet I looked up must have had the pins backwards from the transistor I was using because it was in right according to the datasheet but as soon as I swapped the collector and emitter pins it started working beautifully.With your help, we have just solved the transient issue. I'm now getting 30V with no spikes. I'm going to redesign my boards to reflect this change and redo redwire's version for him as well. His outputs are the smoothest thing I've seen on my scope so there must be some real value to the voltage regulator he added in to replace U1. I think a rev. 7 is in order. Would you like to do it or should I? Quote Link to comment Share on other sites More sharing options...
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