RL Circuit and Ripple Reduction
RL Circuit Basics
For an RL series circuit:
V(t) = VR + VL = IR + L(dI/dt)
Impedance Approach (for Ripple)
For ripple frequency ω:
ZR = R
ZL = jωL
Z = R + jωL
|Z| = √(R² + (ωL)²)
Ripple Current
If ripple voltage is Vr:
Iripple = Vr / √(R² + (ωL)²)
Key Insight
1. Low Frequency Ripple
ωL ≪ R
Iripple ≈ Vr / R
Inductor has little effect.
2. High Frequency Ripple
ωL ≫ R
Iripple ≈ Vr / (ωL)
Strong ripple reduction.
Ripple Reduction Factor
Ripple Reduction = R / √(R² + (ωL)²)
- Larger L → less ripple
- Higher frequency → less ripple
- Larger R → more ripple
Physical Meaning
- Resistor affects both DC and ripple
- Inductor resists only changing current
RL smooths current but wastes power in R
Time-Domain View
Ï„ = L / R
- Large Ï„ → smoother output
- Small Ï„ → more ripple passes
Summary
- RL reduces ripple using inductive reactance
- Effectiveness depends on ωL / R
- Works better at high frequency
- Less efficient than LC filters