In the last few days I spent working with NPN transistors and measuring their characteristics. My aim was measure VBE and IE when transistor will turn on (transistor as switch). For all tests VCE = 3.3V.
I started with S9013. I got data like these:
VBE=0.5V ; IE = 0.007mA VBE=0.6V ; IE = 0.05mA VBE=0.8V ; IE = 100mA
(there is a jump from 0.6V to 0.8V when transistor is turned on)
When I tried to measure the same for BC546B, I got:
VBE = 0.5V ; IE = 0.004mA VBE = 0.6V ; IE = 0.17mA
around VBE=0.68V, the transistor turned off and VBE started to jump around from negative to positive values.
According to a datasheet VBE(SAT)=0.7V; VBE(ON)=0.55-0.7V.
Could someone explain me what happened? The transistor was new. I wouldn't expect that it's broken.
Update. Answer for questions in the comments: There isn't any resistor to limit current via led diode. I considered resistance of diode as limiting factor for current. Transistor case wasn't hot. The current was too small during measuring.