Leaderboard

Transistors are all different. There are good ones and there are poor ones. The worst (but still passing) 2N3055 transistor has a collector to emitter leakage current of 0.7mA but a good one has much less. The collector-base leakage current is much less (a maximum of only 3.5uA at 25 degrees C) then it is amplified maybe 200 times by the current gain of the transistor so the 1k resistor from base to emitter completely kills the leakage current. R16 in our project is the "R" for the output transistors so they do not have leakage current. If R16 is missing then the output transistors will amplify their collector-base leakage current which will cause them to turn on.

The collector-base junction of a transistor has a small leakage current that increases when the temperature increases. The current gain of a transistor amplifies the resulting base current which turns on the transistor. R16 shunts the collector-base leakage current away from the base. Of course not, the collector-base leakage current causes Q4 to turn on. Leakage current and dielectric absorption in C7 causes the output voltage to rise when the load current is zero or is low. The datasheet for a 2N3055 transistor shows that its maximum collector to emitter leakage current is 0.7mA when it has a Vce of 30V, it is at 25 degrees C and it has no base current with its base not connected.