How an LCD Rectifier Works

LCD rectifiers add an extra diode to reduce coil-capacitor interaction.

Rectifiers are circuits that convert Alternating Current (AC) to Direct Current (DC). Traditional rectifiers have three parts: the transformer reduces voltage level, the bridge converts AC to rippling DC and the filter smoothes out the DC.

Name

The name is confusing, but "LCD rectifiers" have nothing to do with Liquid Crystal Displays. The LC part of the name comes from "LC Filters" and the D comes from the fact that a diode is added to an LC filter. An LCD rectifier is one that has an LC filter with an added diode.

Function

The reason for adding a diode to an LC filter is to interfere with the interaction between the action of the coil and the capacitor. These components work together to oppose large changes in current by storing excess energy at excess levels and returning it during periods of low energy -- thereby smoothing out fluctuating DC.

Benefits

Interfering with the interaction between the coil and capacitor allows you to use a smaller -- and therefore cheaper -- coil to achieve the same smoothing effect as an LC filter without the diode. This leads to a much cheaper rectifier of equal quality.

References

• PowerPulse: Designing LCD Rectifiers for Line and Load Variations
• AllAboutCircuits: Rectifier Circuits
• York: LC Filter Design
• PBS: Diodes

Resources

• ElectronicDesign: Build Your Own Low-Cost Driver For A Synchronous Rectifier