Velleman projects EDU06 Assembly instructions - Manual (Page 15)

15
Can we measure this amount of ripple?
Yes we can, a scope is the ideal tool for ripple measurement.
Flip SW1 back to single phase rectifi cation.
Default, your scope starts up with ‘DC-coupling’ selected.
Change that to ‘AC-coupling’
(see manual for how-to instructions).
Now, the scope will only show the AC part of the signal, the DC
part will be blocked. Make sure it is still in ‘auto-setup’ mode.
If you look at the screen below and your scope screen, you
will see a kind of ‘sawtooth’ waveform, this is the ‘ripple’ volt-
age that rides on top of your DC voltage. During the rising
edge the power supply charges the capacitor, during the
falling edge the capacitor supplies current to the circuit.
If more current is drawn from the supply the ripple will be higher, as the capacitor will be drained
more, so it will not be able to keep the output as steady as it would with a small load.
How can we reduce the ripple?
Try fl ipping SW1 for single phase to dual phase rectifi cation
and watch the screen. Check the lower right hand corner.
It displays the rms ripple voltage.
Flip the switch back and forward. It is clear that ripple is
reduced when dual phase rectifi cation is used.
Smoothed versus unsmoothed DC (ripple)
D
C
Good to know: Use 1000 μF per ampère, so e.g. if you design a 2A power supply,
you need a smoothing capacitor of at least 2000 μF (2200μF is the closest value that
is suited for your purpose).