The TIP122 is an NPN Darlington pair transistor. What is TIP120 NPN Darlington Transistor? This article discusses one of the types of NPN Darlington transistors like TIP120 NPN Darlington Transistor – pin configuration, specifications, and its applications. There are many NPN Darlington transistors available in the market like MPSA13, TIP120, PZTA29, BD679, 2N5306, etc. So it works & frequently packaged as a single transistor. This Darlington configuration has a higher current gain as compared to every transistor taken independently. Ie, if I hit the gate with 5V from the Arduino, then the max current that'll flow from drain to source (with 24V supply to the CV) is 5/0.035 = 143mA and the CV will still only draw its 33mA from the supply.A semiconductor device like a transistor is one of the basic building blocks within modern electronics mainly used for switching or amplifying electrical signals & power whereas the Darlington transistor has a multi-transistor configuration that performs like a single transistor that includes one base, emitter & collector. Now, if I instead decide to use a MOSFET, can I still use it as a switch? : if the collector current allows 10mA and the CV (control valve) wants 33mA, then the CV will only get 10mA BUT if the collector current is switched on to allow 100mA, the CV will still only draw 33mA, right? it won't force 100mA through the CV?) But what is actually limiting the current is the amount that control valve will draw (ie. Okay so (for a Darlington/BJT), the calculated collector current is just how much current would be allowed to flow from the collector to the emitter. Thanks for this explanation! I think I had it completely wrong before. Transistors do not pull current from a supply. The "harder" it's saturated the lower the voltage drop/loss across the transistor, which means the transistor will run cooler and more voltage will be delivered to the solenoid. Otherwise you generally want to fully-saturate the transistor. There should also be maximum rating for the transistor's bas-emitter current and you wouldn't want to push that either. There the Arduino is rated for an absolute maximum of 40mA or 20mA "recommended maximum" and there's no need to push that to the limits. But saturation isn't exactly like a light switch and I'd probably "slam it harder" with maybe 10mA into the base of the transistor. How am I in the saturation region?Īll good! If you calculate a collector-emitter current that's more than you can actually get, with the current limited by the solenoid's resistance you are in the saturation range. Now, I am talking to a friend who said that I'm operating in the saturation region so current won't be amplified at a linear rate like my assumed 1000. I used 1.3V as the assumed voltage drop of the transistor. So at the 5V output pin on the controller, I need a resistor Rb = (5-1.3)/0.165mA = 25.5kOhm. I bumped this to 0.165mA to ensure we have enough current. How am I in the saturation region? I've attached a photo of my schematic for reference (note that CV1 and CV2 are the pinouts for the solenoid control valve): Using a transistor (this one ) that has gain of 1000 (depending on Vce and Ic?) and has high enough voltage rating (60V Vce and Vcb). My calculations were as follows: need 33mA current at collector (Ic). Next, I had originally been doing calculations to see what current limiting resistor I needed at the 5V output pint form the controller to make sure that the amplified current from the collector would be around 33mA. if the valve only needed 10mA of current, would it still be better to use a transistor instead of directly connecting it to an I/O pin? First question: is there any benefit to using a transistor here other than for amplifying current? ie. Now, the mega pins are rated to 20mA output current, so I am thinking about using an npn darlington transistor to switch the solenoid on/off. The solenoid is rated for 24V DC, 0.8W, so I believe current should be limited to 0.8/24 = 33.3mA. I am using the Arduino Mega 2560 as a controller to turn on/off a 5/2 way air solenoid valve. Extremely new to electronics and am getting confused with information online about this.
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