ripple voltage

Ripple voltage is the small, repeating wobble that rides on top of a DC supply that should ideally be flat. No real supply is perfectly smooth: the rectifier refills its capacitor in pulses, and a switching regulator chops at high frequency, so the output is DC plus a little leftover AC. Picture a calm pond (the DC level) with small regular waves on its surface (the ripple) — you want those waves as small as your circuit can tolerate.

It comes in two flavours from two sources. In an unregulated or rectified supply, ripple is the low-frequency sawtooth (100 or 120 Hz) as the reservoir capacitor discharges between mains peaks; you estimate it as ripple roughly equals I times t / C. In a switching regulator, ripple is the high-frequency sawtooth at the switching rate plus sharp spikes at each switching edge. Ripple is usually quoted peak-to-peak or as RMS. Example: a 5 V rail with 50 mV peak-to-peak ripple is 1 percent ripple — fine for digital logic, but possibly intolerable for a sensitive ADC reference or an audio preamp.

Why it matters: ripple is a top source of real-world bugs. It shows up as hum in audio, as bands or flicker in video and displays, as jitter in clocks, and as noise added to every measurement an ADC takes off that rail. You fight low-frequency ripple with a bigger reservoir capacitor and with a regulator (whose ripple rejection cuts it further); you fight switching ripple with good output capacitors, small layout loops, and often a small LC or ferrite-bead filter, plus local decoupling at each chip. Knowing the frequency tells you which weapon to reach for.