BC, BC, BC High Current Transistors NPN Silicon Features. Base NPN Epitaxial Silicon Transistor Absolute Maximum Ratings Ta=25 C unless otherwise noted Symbol Parameter Value Units VCER Collector-Emitter Voltage at RBE=1K? : BC 45 V: BC 60 V: BC V. BC BC VCEO. Vdc. Collector – Base Voltage. BC BC BC VCBO dimensions section on page 4 of this data sheet. ORDERING. DATA SHEET. Product specification. Supersedes data of Apr Oct DISCRETE SEMICONDUCTORS. BC; BC; BC

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Essentially you’ll use one of these circuits:. If the 5V rail drops before the power to the Arduino, perhaps if they are powered bbc637 separate rails, all the current to the LED will come from the base, and thus from the Arduino. A forced beta of 20 is usually good. It seemed superfluous at the time, but it makes a better answer. It would be awesome if we could, it would make many circuits simpler, but it’s simply too unreliable to be of any practical use.

This is perhaps the easiest to understand, because it’s as intuitive as the common emitter switch, but you only have to calculate the load resistor. I’m glad you’ve done the calculations, that’s a good start.

BC637 Datasheet, Equivalent, Cross Reference Search

Look at this spread from the datasheet: This works if the voltage drop across the LED is small enough that you have some “headroom” left across the resistor. Spehro Pefhany k 4 The idea is however that the Arduino should drive the transistor fully on so it’s saturated, passing as much current as it can, or at least enough so that the transistor is not the limiting factor. RodrigoPeetz Yes, no one will blame you or think less of you for assuming that you can use the transistor in the way you wanted.


The goal is to drive enough current through the base to make this happen. As you can see, there is no base resistor. The series resistor at the gate is there to limit the switching current, and the resistor from gate to ground is there to make sure that the gate is not floating while the pin is in a high-impedance state that is, an input or turned off. This can be seen as a current booster.

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The current gain varies a lot depending on all sorts of things: The voltage at the collector does not have any say in the current through the LED, which is another benefit. Since the output from the Arduino will be close to 5 volt, and V BE can be treated roughly as a diode, you will have about 4. Common emitter switch This is the traditional “Transistor-as-a-switch” datashest, and is similar to what you have right now. A circuit that relies on a specific current gain will simply not work well.


The voltage V CEbetween the collector and emitter, is called the saturation voltage and is usually small enough to be neglected. Is my calculation correct?

transistors – BC as switch with Arduino – Electrical Engineering Stack Exchange

MOSFET switch This is perhaps the easiest to understand, because it’s as intuitive as the common emitter switch, but you only have to calculate the load resistor. Look at this spread from the datasheet:.

There must be vatasheet, thousands of instructions out there on how to drive a LED with an Arduino, and the best method will be slightly different depending on the voltage drop across your LED. A little warning however: I’d sure like to see the documentation that claims this is the recommended value.

Will it work the way I planned? A conservative number is one tenth of the current through the collector. You calculate the resistor value by looking up the voltage drop across the LED for the current you want, then observing that the voltage drop across the resistor will be the voltage from the Arduino pin minus 0. Email Required, but never shown. Then you pick a base resistor to make sure the transistor is saturated. That’s how I select transistors.