Hey guys,
I am just a hobbyist, and this is the first time I have looked into using a Darlington NPN transistor, a TIP142.
I want to use it as an on/off switch (no amplification). I want to use this switch to turn a high power infrared LED (100w), at 3.5 amps, completely on and completely off. I furthermore want to pulse the base, held at a Thevenin voltage (voltage divider bias) with square waves derived from a 555, using capacitive coupling.
Everywhere I look on the web, every article says that the Vbe drop for a silicon Darlington is approximately 1.4v (2x.7v), and the Vce(sat) drop is approximately .1 to .2 volts + 1 Vbe(.7), for a rough total of .8 volts.
However, in the attached datasheet, I see a Vbe(on) of 3V, A Vbe(sat) of 3.5v, and a Vce(sat) of 2-3V.
Can anyone help me to understand this? Is this just a result of doping the silicon?
All I know is that I want to use the Darlington transistor as a switch at ELF frequencies.
All of your help is appreciated.
I am just a hobbyist, and this is the first time I have looked into using a Darlington NPN transistor, a TIP142.
I want to use it as an on/off switch (no amplification). I want to use this switch to turn a high power infrared LED (100w), at 3.5 amps, completely on and completely off. I furthermore want to pulse the base, held at a Thevenin voltage (voltage divider bias) with square waves derived from a 555, using capacitive coupling.
Everywhere I look on the web, every article says that the Vbe drop for a silicon Darlington is approximately 1.4v (2x.7v), and the Vce(sat) drop is approximately .1 to .2 volts + 1 Vbe(.7), for a rough total of .8 volts.
However, in the attached datasheet, I see a Vbe(on) of 3V, A Vbe(sat) of 3.5v, and a Vce(sat) of 2-3V.
Can anyone help me to understand this? Is this just a result of doping the silicon?
All I know is that I want to use the Darlington transistor as a switch at ELF frequencies.
All of your help is appreciated.