2N2222A can allow collector current upto 800mA and also has power dissipation of 652mW which can be used to drive larger loads than compared with BC547. But there are two important features that distinguish both. The 2N2222A transistor is very much similar to the commonly used NPN transistor BC547. When base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region and the Base Emitter voltage could be around 660 mV. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (V CE) or Base-Emitter (V BE) could be 200 and 900 mV respectively. When this transistor is fully biased, then it can allow a maximum of 800mA to flow across the collector and emitter. To bias a transistor we have to supply current to base pin, this current (I B) should be limited to 5mA. The maximum amount of current that could flow through the Collector pin is 800mA, hence we cannot connect loads that consume more than 800mA using this transistor. 2N2222A has a gain value of 110 to 800, this value determines the amplification capacity of the transistor. Note: Complete Technical Details can be found in the 2N2222A datasheet, given at the end of this page.īC549, BC636, BC639, BC547, 2N2369, 2N3055, 2N3904, 2N3906, 2SC5200 2N2222A Equivalent TransistorsĢN2907(PNP), 2N3904(PNP), 2N3906 (PNP), BC637, S9014, BC148, 2N4403, MPS2222, PN2222, KN2222, KTN2222ĢN2222A is a NPN transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. Collector Emitter Voltage (V CE) is 30V.Continuous Collector current (I C) is 800mA.So, removing the LCD shield and wiring everything directly into the Arduino with a separate push button, everything started working as expected. Eventually, after many attempts at getting the circuit to work, even the LED stopped working and that's when I realised that there must be a continuity problem with the header connections. This would explain the anomaly that only the LED lit up as expected, but the fan failed to work: presumably the weak current into the transistor's Base created sufficient gain to power the LED, but not the fan. It seems that the LCD shield I was using has some fault which only allowed limited current to flow from the corresponding Arduino pins. As the LCD shield occupies all the header pins on the Arduino, the LCD shield helpfully provides circuit connections for the unused Arduino pins. As mentioned in the question, I was using a button wired into an LCD shield. So the question is, why does the circuit work as expected for the LED, but not for the fan? Any help/suggestions will be greatly appreciated! I've tried different pins on the board, but always get the same result. But in my case, the current from the relevant digital pin to the transistor's base never goes higher than 1.4mA. My understanding is that an Arduino digital pin should easily supply this. Measuring the current from VIN (or the 5V pin) to base, I get 4mA, so my assumption is that 4mA is sufficient to saturate the base. If I take a wire directly from VIN or the 5V pin and touch it to base (through a resistor, of course), it does succeed in saturating the base, and the fan turns on. It does turn the LED on and off as expected, but the fan needs much more current than the LED. The problem that I have is that the Arduino's digital pin doesn't seem to be able to saturate the base, so not enough current passes through the transistor to power the fan. My expectation is that, when I press the button, the digital pin wired to the transistor's base will cause the transistor to close the circuit and turn the fan (and LED) on for five seconds. the relevant digital pin is switched from LOW to HIGH for a determined time in response to a button press recorded on A0.įor simplicity, I'm showing a separate button component in the diagram, but I'm actually using a button that's wired into an LCD shield. I'm using a 2N2222 transistor as a low-side switch to turn a 5V computer fan on and off with an Arduino digital pin, which responds programmatically to a button press - i.e.
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