Now, we know from our reading of the motor specs, that the stall current is much, much higher, 500mA. Out of curiosity, I placed my finger against the tip of the motor shaft to create drag and see how much current it would start to draw, and it started to climb instantly, eventually stopping the motor at 130mA.
2n3904 transistor base emitter collector code#
The code to run on the microcontroller is as pretty dead simple as it gets: setup digital 3 as an output and drive it low and high, waiting 5 seconds between states.Īfter hooking it all up, it drew 3.30mA at the Base and 92.0mA at the Collector. Since Power = Volts x Amps, we have \(\mathrm \]ġ230Ω isn’t a standard value, so we’ll go with a 1200Ω resistor. The device is able to dissipate a total of 625mW of power. Now let’s look at thermal characteristics… The only one we’re even close to, is the Emitter-Base voltage, but that would require hooking the thing up backwards, so as long as we’re careful where we put our jumper wires, we’ll be fine.
Since we’re going to be powering this thing with low voltage sources, in this case the 5V Arduino pin, we’re well within the voltage maximums described: Collector-Emitter max of 40V, Collector-Base max of 60V and an Emitter-Base max of 6.0V. Let’s start by understanding our voltage and current limitations. I have to cut it into more reasonable chunks, so that’s what I’ve done here, with a liberal cutting and pasting. Trying to read that whole datasheet at once, cover to cover, is a recipe for disaster. You can refer to the datasheet from Fairchild Semiconductor for all of the ratings that we need. It can wind up getting pretty toasty too, particularly in amplification circuits, consequently, there are thermal characteristics that might need to be taken into consideration.īecause of the semiconductor material this thing is made out of, it has forward voltage drops just like a diode does, referred to as the Collector-Emitter Saturation Voltage and the Base-Emitter Saturation Voltage.įor this initial circuit, we’re not going to do anything other than build something that proves we can pull the correct information out of the datasheet and assemble it so that it produces expected results. The whole transistor, overall, has a maximum current rating called the “Collector Current – Continuous”, we we’ll need to take that into account when planning any kind of circuit (hello current limiting resistors).
The amount of amplification, also referred to as “DC Current Gain”, “hFE”, or just the Greek letter ß, can vary from 20x to 300x depending on the current at the Collector, so you have to have a good sense of what kind of load you’re going to be putting on the thing. The Collector / Emitter current can be many times greater than the current supplied to the base, which is why these things work as amplifiers. It has three pins: Collector, Base and Emitter, and since it’s an NPN, current will flow from the Collector to the Emitter when current is applied to the base. Before we actually put this together, we do have to know a few things about the transistor.įirst, it’s an NPN transistor, specifically a 2N3904, which is about as common and standard as they get. For our first circuit, we’ll keep it nice and simple: a 2N3904 transistor, two resistors and some voltage supplied by our friendly Arduino.
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