Biasing Transistor

[Jack// ani]

Hi all,

Placing a finger on the base pin of this darlington configuration
glows the LED (in fact reaches very close to saturation)!

I learned that you need a threshold voltage of about 0.7volts across
the base-emitter junction in order to bring transistor into
conduction.

So does this imply that my finger having a potential of 0.7volts??

Thanks



VCC
+
|
|
.-.
| |
| |
'-'
|
|
V LED
-
|
-------|
| |
|/ |
o--------o| |
|> |
| |
| |/
-----|
|>
|
|
|
|
|
|
===
GND

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

 

[Rheilly Phoull]

"Jack// ani" <nospam4u_jack@yahoo.com> wrote in message
news:86040da6.0411130401.619a3ff9@posting.google.com...

Hi all,

Placing a finger on the base pin of this darlington configuration
glows the LED (in fact reaches very close to saturation)!

I learned that you need a threshold voltage of about 0.7volts across
the base-emitter junction in order to bring transistor into
conduction.

So does this imply that my finger having a potential of 0.7volts??

Thanks



VCC
+
|
|
.-.
| |
| |
'-'
|
|
V LED
-
|
-------|
| |
|/ |
o--------o| |
|> |
| |
| |/
-----|
|
|
|
|
|
|
|
===
GND

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

More like the finger has a resistance of a few K's. For real saturation just
moisten the digit.

--
Regards ........... Rheilly Phoull