Sometimes I buy stuff to later figure out what to do with it. This is also known as the “solution looking for a problem” approach. The solution of today is a TIP120 Darlington transistor. The question of today is: what can I do with it?
I decided to explore the active region of the TIP120. I have built the circuit below with the following features:
I found that as I increased the base current Ib from 112 uA to 114 uA (in like a gazillion steps), the collector current Ic went up from 0 to 151 mA and Vce dropped from 3 to 1.44 V. At this point Ic is limited by the 10 ohm resistor and not because the transistor is saturated. Beta was well above 1000. This was pretty much what I expected as it agreed with the Youtube tutorials I watched this morning.
What surprised me is the fact that it took quite long to settle after I had changed the base current. Sometimes even more than 10 minutes. Also the setup shows a lot of hysteresis.
Now here comes my question: If the active region of this Darlington transistor is so “unstable”, what can it be used for? I can imagine that the TIP120 can be used as a switch, but wouldn’t a MOSFET be a better choice? What can I use a TIP120 for?
I guess that were three question instead of one. Is that too much?
I decided to explore the active region of the TIP120. I have built the circuit below with the following features:
- The 10 ohm resistor is rated for 20 W.
- The 470 ohm resistor limits the base current to 6.4 mA.
- The 50k resistor is a 10 turn pot, which gives me the ability to set the base current with 0.01 uA precision.
I found that as I increased the base current Ib from 112 uA to 114 uA (in like a gazillion steps), the collector current Ic went up from 0 to 151 mA and Vce dropped from 3 to 1.44 V. At this point Ic is limited by the 10 ohm resistor and not because the transistor is saturated. Beta was well above 1000. This was pretty much what I expected as it agreed with the Youtube tutorials I watched this morning.
What surprised me is the fact that it took quite long to settle after I had changed the base current. Sometimes even more than 10 minutes. Also the setup shows a lot of hysteresis.
Now here comes my question: If the active region of this Darlington transistor is so “unstable”, what can it be used for? I can imagine that the TIP120 can be used as a switch, but wouldn’t a MOSFET be a better choice? What can I use a TIP120 for?
I guess that were three question instead of one. Is that too much?