The source resistance (
) of the function generator is 50 ohms.
We used this fact to our advantage in Lab 1 to convert it into
a pseudo current source,
but sometimes it works against us.
If we want to drive a low resistance load (e.g. a motor)
with a voltage, there will be a
voltage drop across
the internal resistance of the function generator.
This means that the voltage actually delivered to the load can be
significantly less than that generated by the source.
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Step 1: |
Set the function generator to produce a 100 Hz sine wave.
| |
Step 2: |
Turn the function generator
AMPLITUDE
fully counterclockwise.
Pull out the
DC OFFSET
control and adjust it until
the output is 4 V.
| |
Step 3: |
Adjust the
AMPLITUDE
control so that
the signal
has a p-p amplitude of 6 V.
| |
Step 4: |
Connect a 47 ohm resistor to the function generator output.
| |
Step 5: |
Wire the following circuit. |
|
Note that this inserts an emitter follower buffer between
the function generator output and the load.
| ||
Step 6: |
With the scope, measure 
.
Sketch the waveform, noting the p-p and average value.
| |
Step 7: |
Compute the voltage gain,
and the offset
.
| |
Question 3: |
Compute the
average
power
delivered to the load (
)
and dissipated by the transistor (
).
The power rating for the load resistor is 1/4 W
and for the transistor is 625 mW.
Have we exeeded the rating of either component?
| |
Step 8: |
Replace the 47 ohm resistor with a 470 ohm resistor.
Measure
and compute the voltage gain and offset.
Are they significantly different from the previous values?
|
