Transistor as a switch BJT NPN

399

06:14:28

Example of bipolar (BJT) N-channel (NPN) transistor used as a current-driven switching device to turn on an LED. It drives possibly much higher current with much smaller current induced by logic-level circuit  (voltage <= 5V), possibly coming from Arduino PWM control pin. Base resistor needs to be calculated carefully to provide desired driving current. 

see also my example of MOSFET: http://everycircuit.com/circuit/5224206555414528

published 8 years ago

Jalaj

8 years ago

Why are you using 14V Source to drive LED and that too without Resistance ? There are no 12V LEDs available in market !!

Jalaj

8 years ago

You can check out my transistor circuit

marioandre

8 years ago

Ttt

rich11292000

8 years ago

Here is a 12 volt led: https://www.amazon.com/Qty-Lights-wired-volt-leds/dp/B007O1X12C

jediz

8 years ago

the 12V LED represents a LED strip, it's just an example, more focused on how the transistor works rather than modelling the LED circuit properly -- You could as well put a resistor there

rich11292000

8 years ago

What jalaj is referring to is that you always need a current limiting resistor. Even when a transistor controls the current, the transistor will heat up and cause 'thermal drift'. This means current will increase as heat increases, and eventually failure.

rich11292000

8 years ago

See hurz' example: http://everycircuit.com/circuit/6367186154684416

jediz

8 years ago

In my example the 12V LED strip does have resistors included so I omitted those, but you're right. Added a resistor to make it obvious.

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