Cirrus-logic AN376 Manual de usuario descargar pdf (Pagina 1)

Cirrus Logic, Inc.

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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

OUT

AC/DC

LED

Driver

AC Line

Voltage

OUT

Figure 1. Rectified AC on Output

AN376

JUL’13

AN376REV2

1 2 3 4 5 6 7 8 9

Indice de contenidos

Pagina 1 - Application Note

Pagina 2 - 2.1 Design Considerations

AN3762 AN376REV22. Design ProcessSince the assumption is that the power factor is equal to 1 and the current obtained from the AC line is sinusoidal,t

Pagina 3 - 2.2 Design Example

AN376AN376REV2 3For a given capacitance COUT and resistance RLED, the amount of attenuation can be calculated by recognizingthat the output stage can

Pagina 4 - 2.3 CS1615 Example

AN3764 AN376REV2For the design example, the maximum ripple current Iripple specification is ±40% on the RMS output current of250mA, which is equal to

Pagina 5 - 2.3.1 Measured Results

AN376AN376REV2 5Equation 6 on page 3 is used to calculate the attenuation factor:Since the RC network attenuates the sinusoidal component by 40%, the

Pagina 6 - 4.1 References

AN3766 AN376REV23. SummaryAs a starting point, calculate the RC filter attenuation factor to reduce the ripple current before selecting the finaloutpu

Pagina 7 - 4.2 CRD1615-8W Schematic

AN376AN376REV2 74.2 CRD1615-8W SchematicFigure 5. CRD1615-8W Schematic=B5(9B&zoll{vmzoll{lunpullykh{lkyh~uGiwhy{GJzoll{[VY\VYWXZjUsht

Pagina 8 - Revision History

AN3768 AN376REV2Revision History Revision Date ChangesREV1 APR 2013 Initial release.REV2 JUL 2013 Content updated using PCBA Rev C.

Pagina 9 - IMPORTANT NOTICE

AN376AN376REV2 9Contacting Cirrus Logic SupportFor all product questions and inquiries contact a Cirrus Logic Sales Representative. To find the one ne

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