Velleman projects EDU06 Assembly instructions - Manual (Page 14)

14
Experiment 6: Smoothed versus unsmoothed
DC (ripple)
Connection layout:
Connection summary:
GND clip : 4
Probe tip : 6
Purpose:
The purpose of this experiment is to show what smoothed and unsmoothed DC looks like on a scope
screen and how a scope can help you to determine the quality of your DC supply.
A little theory:
In the previous experiments, we have used one or more diodes to convert an AC voltage into a DC volt-
age. The result was OK, but far from perfect.
Why? Because it was still far from the fl at line one would expect when measuring a perfect DC voltage.
It is clear that our rectifi ed AC voltage needs ‘smoothing’. This can be done with an electrolytic capacitor
(see diagram of this board)
How?:
Place the probe switch “x1/x10” to ‘x1’. 1.
Make sure to fl ip SW1 to the correct position. 2.
Turn on the HPS140 Handheld Pocket Scope, It will start-up in auto setup mode as always. 3.
Watch the screen closely. You will notice that the trace is almost fl at, so the capacitor is doing a
good job at smoothing our rectifi ed AC voltage. Yet, it still wobbles a bit.
If you fl ip the switch from single phase to dual phase rectifi cation,
the wobbling will be reduced.
Why is this?
Basically, the capacitor acts as a temporary storage device.
It provides power to the rest of the circuit during the ‘interruption’ of the waveform (remember, single
phase rectifi cation?). With dual phase rectifi cation this interruption is not present, so the capacitor has
less work to do. The remaining ‘wobble’ of the waveform is called ‘ripple’. One of the key features of a
good DC supply is low ripple.
NOTES:
Smoothed versus unsmoothed DC (ripple)
Connection summary:
.
e, It will start-
es a b t
of the waveform (remember, single
n is not present so the capacitor has