This is an LED driver circuit, but what is the use of the transistor in it?
Electronic – the use of the transistor in this circuit
transistors
Related Solutions
To select a switching transistor, you'll need to know how much current will flow through your 12V LED. Choose an NPN transistor that can pass that current, allowing a good margin of safety. You're looking for the Ic(max) parameter in a data sheet.
Related Topic
- Electrical – (Infrared LED Circuit) Can i use this circuit with 3.3v logic
- Electrical – What are the alternatives of the transistor 2sc9013
- Electronic – Why does this transistor circuit light the LED
- Electronic – What this NPN transistor circuit do
- Electronic – Why isn’t the current split between the transistor and the LED in this NOT transistor circuit
- Electronic – the purpose of this transistor in this circuit
Best Answer
The 7805 regulator is setup as an adjustable regulator as adjusted by the 10K pot. The transistor is connected as an emitter follower to increase the load current available to the LED load. Supposedly the 7805 is not able to supply the load current needed for the LEDs and so the transistor acts as a current booster.
This circuit has a fundamental problem in that there is no current limiting for the LEDs. Normally this current limiting would be supported with some resistors in series with each LED string.
There is also the additional problem that each of the three LED strings will have a different total LED forward voltage drop. The string with the lowest voltage drop will try to take most of the current from the transistor. This can lead to brightness variation between the LEDs. Once again this problem is solved by having resistors in series with each LED string to balance the current in each string.
BTW this is typical of crap circuits you find published on the web.