Thursday, 24 March 2016

transistors - BJT base connected to ground and still operates?


When in university I used to get confused how a transistor (NPN) can draw current from ground. I'm now studying power amplifiers and again, this same configuration appears. How does Ir draw current from seemingly nothing/ground? enter image description here



Answer



Simply redraw the circuit and you will see from where this base current is coming from.


schematic


simulate this circuit – Schematic created using CircuitLab


As you can see the \$Q_2\$ base current is coming from \$\textrm{Vee}\$ voltage source.


And flows this path:



+Vee--->R1---> Q2 base-emitter junction--->-Vee


And remember that in the electronic ground is just a reference point, not a real Earth ground. And we are measure all our voltage with respect to this reference point called ground.


enter image description here


To measure the voltage we need two points in the space. One of this point is treated as a reference point.


We have a very similar situation when we try to measure a height of an object. We need a reference point. The most common reference point is "above mean sea level".


But when you measure the height of the table in your house the floor now becomes your reference point.


No comments:

Post a Comment

arduino - Can I use TI's cc2541 BLE as micro controller to perform operations/ processing instead of ATmega328P AU to save cost?

I am using arduino pro mini (which contains Atmega328p AU ) along with cc2541(HM-10) to process and transfer data over BLE to smartphone. I...