14-11-2012, 01:57 PM
Voltage Regulator
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In your robot, the energy is derived from batteries. Specifically,
there are two sets of batteries wired up to act as voltage sources; a
9V battery, and two 1.5V batteries in series that act as a 3V source.
Since different circuits in your robot require different voltage
sources, it is not always possible to hook up the battery directly to
power the circuits. The ICs in your robot circuit are designed to
work with a constant 5V source. Therefore, it is important to convert
the 9V source into a 5V source. Since a DC voltage (one that is
fixed over time such as a battery) is being converted to another DC
voltage, the circuit that does this is called a DC-to-DC converter or
a voltage regulator. If we were to convert 110V AC (alternating
current - like the power in a wall outlet) into a 5V DC source, the
circuit would be an AC-DC converter.
Laboratory Exercises
Next, we will explore what is called the “load regulation”
of your voltage regulator. Good load regulation means
that the output voltage does not change much with
changing load resistance. To characterize the load regulation
of your regulator circuit, set the power supply
voltage at 9V, and see how the output voltage varies as
you draw current from (load down) the voltage regulator
output. Measure the regulator output voltage with a
4.7KΩ resistance (which means a load current of about
1mA) and with a load resistance of two 4.7KΩ resistors
in parallel (which means a load current of approxiAnalog
Laboratory Exercises 49
mately 2mA). We formulate the voltage regulator’s
load regulation in terms of its incremental output resistance
- the change in load voltage divided by the change
in load current