Discussion in 'Homework Help' started by andy24691, Jan 21, 2011.

1. ### andy24691 Thread Starter Member

Nov 25, 2010
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What does the AC load line represent on a output characteristics graph for a transistor amplifier circuit?

2. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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The bias area for clean operation, if you are talking about the line drawn a 45 degrees across the curve tracer plot. It will also allow you to get the output voltage for an input voltage, moving the line left and right tells you the best "operating point" or bias level to get the results you'd like.

Nov 25, 2010
42
0

4. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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Dec 26, 2010
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This is a graphical construction used to estimate collector-emitter voltage Vce and collector current Ic in a transistor amplifier. The example appears to be for an NPN common-emitter amplifier with a capacitively coupled external load.

The BJT output characteristic shows a family of curves of Ic plotted against Vce, for different values of Ib.

The DC load line shows the relationship between steady-state Vce and Ic imposed by the power supply voltage and the collector and emitter resistors. The quiescent bias point is indicated at Q, where the DC load line intersects one of the output characteristic curves.

The AC load line allows signal voltage swings to be estimated. At signal frequencies, the transistor output sees a lower impedance, due to the load capacitively coupled to the collector, and most likely also due to elimination of the AC effect of Re by a bypass capacitor. The AC load line is drawn in with an appropriate slope for this lower impedance, passing through the quiescent point bias point Q.

If relatively linear operation is required, this bias point must be correctly chosen.

6. ### hgmjr Moderator

Jan 28, 2005
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Can you supply the schematic of the transistor amplifier circuit that goes with the plot?

hgmjr