PAGE 132 OF 150 · POWER SUPPLIES & BATTERIES
Capacitors for Smoothing Supplies
Smoothing capacitors reduce supply ripple.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Smoothing
Rectified supplies have ripple, a rise and fall between peaks. A capacitor charges at the peaks and supplies current between them, keeping the voltage steadier.
Rule of thumb
Ripple voltage is about I ÷ (f × C). For 0.5 A, 2,200 microfarads and a full-wave rectified 50 Hz supply, which ripples at 100 Hz, the ripple is 0.5 ÷ (100 × 0.0022) ≈ 2.3 V.
- Use electrolytic capacitors with the correct polarity.
- Choose a voltage rating at least 1.5 times the working voltage.
- Add a 100 nanofarad ceramic capacitor near each chip.
Wrong polarity can make an electrolytic capacitor fail.
REMEMBER
A bigger capacitor means smaller ripple.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
Explore LED clocks, stopwatches and electronics at cosycom.com.