Hey...

I need help in understanding an example from the Art of Electronics. Its the emitter follower example on page 67.

Basically, a split supply emitter follower circuit is shown in addition to a diagram of the input and output waveforms which show the output clipped at -5V.

Could anybody explain to me in detail why the output becomes clipped. I have read answers to the same question in other posts but these explanations usually say the voltage divider formed by the emitter resistor and the load resistor halves the -10v negative swing...why isnt the +10v swing clipped for the same reason.

jonny

 

Actually, it is not as complicated to understand as it may appear.

The point that is being made in this example is that the emitter follower cannot sink current into the load. That means that the 1K load resistor together with the 1K emitter resistor are forming a resistor divider that produces -5V at the junction of the two 1K resistors. The emitter base junction in this case is reverse biased once the voltage at the base goes more negative than approximately -4.3 volts.

hgmjr