These transistors may come with straight or preformed leads.If you need a little beefier NPN transistor, look at our PN2222 which can support up to 600mA and if you need more than that, check out our TIP120 Darlington transistor which can handle up to 5A. Using two 100 ohm 1/4W resistors in parallel would be another approach. Power through the that resistor is P = 60mA * 3V = 180mW so a 1/4W resistor will work, though a 1/2W would be a better choice for long-term use. The example assumes an LED voltage drop of 2V, so R = (5V – Vled) / 60mA = 50 ohms. This value may vary a bit depending on what LEDs are being used. The 50 ohm resistor sets the overall current for the 3 LEDs. The 4.7K resistor on the base is there to limit the current out of the uC pin to safe levels and the value is not overly critical. This simple circuit allows you to drive all three LEDs off the same uC pin. You could use 3 pins on the uC to drive the 3 LEDs, but that is a waste of pins unless you have pins to spare. In this circuit the base terminal of the transistor serves as the input, the collector is the output, and the emitter is common. In electronics, a common emitter amplifier is used as a voltage amplifier. In-circuit diagram or schematic which is set circuit in the common emitter. The indicator consists of 3 LEDs which each draw 20mA of current.Ī uC pin can easily drive an LED at 20mA, but this circuit will require 60mA which is outside the range of the typical uC drive capability. Schematic of very Simple preamplifiers using 2N3904. We have an LED indicator that we want to drive. NPN transistors are generally used in low-side switching applications where they are connected between the load and ground. These can be very handy when you need to boost the output of a uC pin to drive something that it can not drive directly. The 2N3904 are a good inexpensive general purpose NPN transistor for low power amplification and switching and should be part of every parts bin.
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