Transistor circuit maximum voltage swing

Replies

• 

  reachrkata

  Ok here goes.
  I presume that you are requesting the output voltage swing calculation for the normal CE amplifier ckt with Rb = base resistor, Rc = collector resistor. Emitter is connected to GND -
  
  To determine the output voltage swing exactly, you need to calculate range on the load lime where the transistor is in active region. Anything in saturation / cut-off means clipping at the output.
  
  1) First you find the Ibmin required for the transitor to just go into active region from cutoff. With the Ibmin*Hfe will give Ic. From this Ic you can calculate the collector voltage value Vc1.
  
  2) Next you find the the Ibmax required for the transitor to just go remain in active region without going into saturation. With the Ibmax*Hfe will give Ic. From this Ic you can calculate the collector voltage value Vc2.
  
  Vc1 ~ Vc2 is the voltage swing you require.
  
  - Karthik
• 

  thaiffer

  Sorry does it make any difference that I have a collector resistor (3.3k ohm) and an emitter resistor (1k ohm).
  
  I measured Ib min is 40nA and Ib max at 8.5uA, my hfe gain is 200 so i calculate that my low value of Ic is 8uA, my high value of Ic i calculate to be 1.7mA.
  
  Reading off from my load line I approximate VC1 at 10V and VC2 at 3.5V.
  
  Can you confirm this is the correct method?
• 

  thaiffer

  I just checked these values of VC on my multisim circuit and can confirm that for VC1 I record 9.9V when the amplifier is just turned on, and VC2 when it just saturates I record at 3.3V.
• 

  reachrkata

  Great !! Then the maximum voltage swing is 9.9 - 3.3 = 6.6V.
  
  This behaviour can also be simulated in Multisim. To your circuit, just give a sine wave input at the base and check the sine wave output at the collector. Verify at the collector that the waveform starts clipping after a peak-peak of 6.6V.
  
  -Karthik
  😁