clc filter calculator

What is a CLC filter?

A CLC filter (also called a pi filter because it resembles the Greek letter π) is a classic power-supply smoothing network made from three reactive elements: a shunt capacitor C1, a series inductor L, and a second shunt capacitor C2. Its main job is to reduce AC ripple riding on top of a DC output.

This topology is popular in linear power supplies, analog front ends, audio equipment, RF bias rails, and other circuits where low-noise DC is important. Compared with a single capacitor filter, CLC designs can deliver significantly better ripple suppression with less load-dependent variation.

How this CLC filter calculator works

The calculator uses your ripple frequency, component values, source impedance, and load condition to estimate attenuation from the ripple source to the output node. It reports:

• Calculated load resistance from DC voltage and current
• Inductive and capacitive reactances at ripple frequency
• Stage attenuation through C1 with source impedance
• Attenuation through L and the C2 || load output network
• Total attenuation (ratio and dB) and predicted output ripple (Vpp)
• Approximate LC resonance and damping indicator

Step-by-step usage

1) Set ripple frequency correctly

For full-wave rectified supplies, ripple is typically 100 Hz (50 Hz mains) or 120 Hz (60 Hz mains). Switching supplies may have much higher ripple frequencies.

2) Enter realistic source impedance

Source impedance strongly affects how much C1 can attenuate ripple. A very low source impedance means C1 has less leverage, while higher source impedance increases C1 effectiveness.

3) Enter load operating point

The calculator derives effective load resistance from Vout and load current. This directly impacts damping and the output shunt behavior around C2.

4) Tune C1, L, and C2

Increasing capacitance lowers capacitive reactance. Increasing inductance raises inductive reactance at ripple frequency. Both generally improve attenuation, but practical limits include inductor resistance, capacitor ESR, size, and cost.

Design tips for better real-world results

• Mind ESR and DCR: Real capacitors have ESR, and real inductors have winding resistance. These losses reduce ideal attenuation.
• Watch resonance peaking: If operating frequency is close to LC resonance and damping is weak, ripple can increase rather than decrease.
• Use ripple-current-rated capacitors: C1 in particular can see significant ripple current.
• Check inductor saturation: Ensure inductor current rating exceeds load current plus ripple margin.
• Prototype and simulate: Use SPICE and bench measurements to confirm noise performance under temperature and load variations.

Example interpretation

If the output shows attenuation of 0.05 (about -26 dB), then a 2.0 Vpp ripple at the filter input is reduced to about 0.10 Vpp at the output. For sensitive analog rails, you might then add a post-regulator or RC stage for additional cleanup.

When to choose CLC vs other filters

CLC is great when:

• You need stronger ripple suppression than a single capacitor can provide
• Current is moderate and adding an inductor is practical
• Power efficiency matters more than simple RC filtering

Consider alternatives when:

• Size or cost of inductors is unacceptable
• Load current is very low (an RC or active filter may be enough)
• You need very tight regulation (use a linear regulator after filtering)

Use this calculator as a fast design aid, then refine with measured component models and application-specific constraints.