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What is the gain of a NPN transistor?
You say the LEDs drop 3 V. Figure about 200 mV for the saturated transistor, which leaves 1.8 V across the resistor. (1.8 V)/ (20 mA) = 90 Ω. The common value of 100 Ω would work fine. You have to consider the gain of the transistor in determining its base resistor.
Can a transistor be used as a driver for an led?
An LED driver is an electronic circuit that utilises a transistor to switch power to an LED. Usually, the signal from a microcontroller, or logic gate, does not possess sufficient drive current to power an LED directly. If the LED has a higher power requirement, then it is best to use an NPN transistor as a driver.
What is the forward bias voltage of a transistor?
Assuming the transistor conducts fully in saturation, there will be negligible resistance across its emitter-collector junctions, and therefore the voltage across the series resistor RL will be 3.3 V. This is very simple to deduce because the forward bias voltage of the LED is 1.7 V,…
What should the base resistor of a transistor be?
From the P2N2222A documentation, we select a suitable minimum current gain value (hFE) of the transistor as 100. We know that the load resistance RL is 165, therefore the following calculation should provide the value of the base resistor.
Can a NPN transistor be used to control multiple LEDs?
The first circuit is entirely adequate unless you value independent control of each LED. The second circuit has the advantage that if desired you can turn individual LEDs on or off independently and the (obvious) disadvantage of requiring more components. Almost any NPN transistor will work. If the LEDs are white they will have ABOUT 3v on voltage.
What kind of transistor is needed for 4 LEDs?
Almost any NPN transistor will work. If the LEDs are white they will have ABOUT 3v on voltage. So I per LED = V/R = (5-3)/560R = 3.6 mA per LED or about 15 mA for all 4 LEDs. Almost any small NPN transistor will work here. Assuming that your LED require 20 mA each, circuit A will require a transistor that can drive roughly 80 mA.
Is it good idea to parallel 4 LEDs?
Paralleling 4 LEDs is not a great idea. It would be better to give each LED its own resistor. You say the LEDs drop 3 V. Figure about 200 mV for the saturated transistor, which leaves 1.8 V across the resistor. (1.8 V)/ (20 mA) = 90 Ω.