Transistor as switch

npntransistors

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.

Schema how I tested it

Best Answer

From your question, you've only shown 2 data points for your BC546B transistor. If you look at the datasheet, here are the electrical characteristics, specifically the base-emitter on voltage

enter image description here

So the minimum is 0.55, and the maximum is 0.7 to 0.77. The manufacturer's datasheet guarantees your transistor will be somewhere within that range.

Right now, you've only shown us 0.5V and 0.6V for Vbe.

I'd also recommend measuring the base current, Ib.

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