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TRANSISTOR BREADBOARD PROJECT

V. Ryan 2002 - 2009

 

PDF FILE - CLICK HERE FOR PRINTABLE WORKSHEET BASED ON WORK BELOW

 

DARLINGTON PAIR PROJECT

   

Components:
680 ohm resistor to protect the LED.
1K resistor from LDR to the base of the NPN transistor.
TWO BFY50 npn transistor (try any alternative).
One 10K preset resistor.
One LDR.
Black and red wire.
   

LAYOUT OF FIRST TRANSISTOR:

   
   

LAYOUT OF SECOND TRANSISTOR

The legs/pins on the second transistor have been twisted slightly to allow them to be pushed into the breadboard in the correct positions:

   

 

   

When a single transistor is used in the circuit, as seen earlier, the LDR has to be completely covered before the LED lights. This is because the circuit lacks sensitivity as the current into the base of the transistor is quite weak. A darlington pair is needed to amplify the current and this is achieved by the first transistors emitter feeding into the base of the second transistor. The current is amplified to a greater level and the LDR has only to be covered partially before the LED lights.

   
 
   

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