a question about transistors

[Bizzy]

Good morning
Can anyone tell me what is the lowest voltage needed in the base of a transistor for it to switch on and allow electricty to flow from the collector to the emitter? Particularly a TIP 120
Thanks
Bizzy

[pese]

Good morning
Can anyone tell me what is the lowest voltage needed in the base of a transistor for it to switch on and allow electricty to flow from the collector to the emitter? Particularly a TIP 120
Thanks
Bizzy

Principalle
Germanium Transistors need about 0,25 volt to switch on
Silicon Transistor 0,7 volts. (up to 3 time for power transistors and fully collector currents!)

so TIP120 and some BDX..  as 33, 53 enz) are
DARLINGTON Transistors.

2 Times Base-Emitter Follower are to  "fill".
So Minimum Voltage to start is 1,4 Volts.
(for fully current even more)

Seaching in google
TIP120 datasheet  , without ""
http://www.datasheetcatalog.com/datasheets_pdf/T/I/P/1/TIP120.shtml

find out the Vbe Caracteristic at the needed IC (Colector Current)

ALS give MANY attenteion ti Vce(sat)

that is the satuartion voltages.
The Transistor will not switch to ZERO volt!!
Evenn an Darlingtin have  higher Satuartion values as
normal Transistors.

For Low saturation use GermaniumTransistors or FETs.

PESE

[mscoffman]

Adding to what pese has said.

In non-mosfet ie bipolar transistors the base drive works based
on current so you need to look at both the base inherent
device resistance and external circuit resistance to get adequate
current at low voltages for things to begin conducting.

Germanium semiconductors, while having very desirable
characteristics, the germanium semiconductor dopants are not
pinned and can migrate - changing their characteristics over time,
although the temperature and base voltage both play a role.

A silicon Schottky semiconductor can have a transfer characteristic
similar to germanium but at slightly more expensive. For high-efficiency
required circuits, I would try to use Schottky semi's to minimise losses
where available.

:S:MarkCoffman

[pese]

Right,

the gaim at darlington transitors is about 10000 times
so it need base current lower than 1 mA  to drive many amps.

Als the vltage level that is need on the Darlington TIP120 is also
about less than 1 Volt to switch the fully needet Amp in Collector load.

More details you find in the datasheets

Gustav Pese

[Bizzy]

Right,

the gaim at darlington transitors is about 10000 times
so it need base current lower than 1 mA  to drive many amps.

Als the vltage level that is need on the Darlington TIP120 is also
about less than 1 Volt to switch the fully needet Amp in Collector load.

More details you find in the datasheets

Gustav Pese

Hi Pese
If What I am understanding then. a TIP 120 would require less than 1 Volt  coming into the base to swicth. is that correct?
thanks
Bizzy