Cirrus Logic AN376 User Manual
An376
Copyright
Cirrus Logic, Inc. 2013
(All Rights Reserved)
Cirrus Logic, Inc.
Application Note
Single Stage Output Ripple Current and the
Effect on Load Current in an LED Driver
1. Introduction
LED lighting requires a switched-mode power supply (LED driver) to provide the low-voltage DC required for the
LEDs from the AC mains supply. Figure 1 illustrates the sinusoidal AC line voltage pulse width modulated to a low
voltage for the output of the LED driver. To determine the amount of output ripple in a given design, a thorough un-
derstanding of the physics behind the PFC converter and the very nature of sinusoidal current in the AC line is re-
quired. To approach the output ripple voltage analysis, first assume that the power factor of the converter is equal
to 1. Second, assume that there is enough output capacitance to maintain the operation of the LEDs above the for-
ward voltage of the LED string and that the output voltage of the converter is a DC voltage.
This application note details the interaction of the output capacitor with AC line voltage and the effect of this on out-
put current ripple. The design example (see section “Design Example” on page 3) demonstrates the relationship be-
tween a specified ripple current and the RC filter circuit. The CS1615 example (see section “CS1615 Example” on
page 5) uses the Cirrus Logic CRD1615-8W reference design to illustrate the attenuation of the output current ripple.
See the CS1615/16 Single Stage Dimmable Offline AC/DC Controller for LED Lamps data sheet for more details
about the CS1615/16 IC. See the CRD1615-8W 8 Watt Reference Design and CRD1616-8W 8 Watt Reference De-
sign data sheets for more details regarding the reference designs. For more information, see section “References”
on page 6.
LED
Lighting
C
OUT
AC/DC
LED
Driver
AC Line
Voltage
I
OUT
Figure 1. Rectified AC on Output
AN376
JUL’13
AN376REV2