WH Tan wrote: > > I wish to control a 13V dc supply with a digital logic high 5V. How to > achieve this purpose by using a general purpose transistor? One PNP transistor, (high side) and 3 resistors. Connect the resistors as a 3 section voltage divider so that when digital pin is at 5v the voltage across B-E is only about 0.4v. When the digital pin goes low the voltage B-E rises to about 0.8v and PNP turns on. :o) -Roman -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics