Hi!
I was wondering what was the use of the resistor in the following circuit:
Thanks!
WB
It still is to limit the current into the base of the transistor. Else the controller output might get damaged, or in theory, the transistor.
@Arduino-NCC-1701
It controls the Matter/Anti-Matter mix.
Live long
The transistor base doesn't work on 5V?
no, it does not. It's not like a logic-compatible MOSFET.
Sorry, but I have no idea what a logic-compatible MOSFET is.
Is there a specific voltage it works on?
Thanks!
...and prosper
Sorry, thought that might be the source of your confusion. It's another, bit more modern, way to turn a device on/off.
Assuming 'it' is a transistor, you may think of the base-emitter junction of a transistor as(more or less) a silicon diode. So somewhere in the 0.5-0.6 V range, it begins to conduct, and by about 0.65V it's full-on. The problem comes in when you connect that to your digital output and set it high; the transistor acts as a short circuit; thus, you need a resistor to limit the current or you'll fry your Arduino..
Good one
No, not transistors like that. The work based on current.
What do you mean by work based on current?
Thanks for the help.
Well, I do know what a MOSFET is, just not a logic-compatible MOSFET.
What you said about a transistor, does this also apply to a MOSFET?
Oh wait a sec. A transistor is current controlled and a MOSFET is voltage controlled?
Hey you are smarter than you think.
Transistors like that have a parameter named Hfe, a magnification factor. Send a current into the base and the collector passes Hfe times that current. Check the datasheet for the transistor to learn its limits. alla gtransistors are different...
Thanks I think I get it.
So would a resistor be necessary if using a MOSFET?
Not needed but will not do any harm and may save your arduino in case you do something stupid...
Due to various technical things a 180 - 280 serial resistor is used between the controller pin and the gate. That's elegant but not not needed for life.
A 10 k resistor from output pin to GND makes it complete.
I tried calculating it, but it doesn't seem to work. Please correct me if I made a mistake.
The TIP120 is a transistor, from what I read, so current-controlled.
So I decided to look up the TIP120 spec sheet. Here's the link I found:
I looked at maximum base current. It said 120mA.
I then tried to calculate the resistance I would need so that I wouldn't surpass these 120mA.
So:
R=?
U=5v
I=120mA = 0.12A
R=U/I
R=5V/0.12A
R= about 41 ohms
so logically I would need about a 50 ohm resistor +- 10%
Then why is the resistor in the photo 2.2 kiloohm???
Did I do something wrong?
Thanks for clearing this up!