- #1
nareto
- 7
- 0
Hello, I have taken some measurments following a proposed experiment in a begginners electronics book to calculate the beta-value of an NPN BJT transistor. The circuit was as follows:
____________
| | |
| | |
+ R_B R_C
9V | C_|
- B
| E
|_______ _|
EDIT: of course it's not clear, at least in my browser. Basically it's a 9V battery with the + that has two branches, one that goes to the Base of the transistor and one to the Collector, each branch has in series a resistor, respectively R_B and R_C. The minus is attached to the Emitter.
hope it's clear... E B and C are the tranistors emitter, base and collector, R_C a 1kOhm resistor and R_B was a resistor whose value changed during the experiment. Also, not shown, there were two amperometers in series respectively with R_B and R_C (to measure I_B, base current, and I_C, collector current) and a voltmeter between C and E (to measure the collector-emitter voltage).
So, what *should* have happened is that, starting with R_B=1MOhm and decreasing this value (I didn't use a potentiometer but different resistors), I should have obtained increasing values of I_B and of I_C in such a way that there ratio, beta=I_C/I_B would be more or less constant.
However, I got the values that can be seen in the image:
http://i.imgur.com/y9EZZ.jpg
With R_B=1MOhm beta is 50, and then it constantly decreases till it reaches 1.2! This is strange...
So, given that I desoldered the transistor out of a previous made PCB, could I have damaged it by desoldering? Is this non-constant-beta-value a typical symptom of having burned out the transistor?
thanks for any help,
renato
____________
| | |
| | |
+ R_B R_C
9V | C_|
- B
| E
|_______ _|
EDIT: of course it's not clear, at least in my browser. Basically it's a 9V battery with the + that has two branches, one that goes to the Base of the transistor and one to the Collector, each branch has in series a resistor, respectively R_B and R_C. The minus is attached to the Emitter.
hope it's clear... E B and C are the tranistors emitter, base and collector, R_C a 1kOhm resistor and R_B was a resistor whose value changed during the experiment. Also, not shown, there were two amperometers in series respectively with R_B and R_C (to measure I_B, base current, and I_C, collector current) and a voltmeter between C and E (to measure the collector-emitter voltage).
So, what *should* have happened is that, starting with R_B=1MOhm and decreasing this value (I didn't use a potentiometer but different resistors), I should have obtained increasing values of I_B and of I_C in such a way that there ratio, beta=I_C/I_B would be more or less constant.
However, I got the values that can be seen in the image:
http://i.imgur.com/y9EZZ.jpg
With R_B=1MOhm beta is 50, and then it constantly decreases till it reaches 1.2! This is strange...
So, given that I desoldered the transistor out of a previous made PCB, could I have damaged it by desoldering? Is this non-constant-beta-value a typical symptom of having burned out the transistor?
thanks for any help,
renato