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Application Note

CS1501 & CS1601:

DRIVING THE ZCD PIN FROM THE MOSFET DRAIN

1. Introduction

The CS1601 is designed with ZCD (zero-current detection), providing the controller with the capabil ity to turn on the MOSFET

when the current through the boost inductor is close to zero. This can also be described as valley/zero crossings switching. This

is implemented by adding a sense windin g on the PFC choke to detect the current.

If the addition of an auxiliary winding on the boost inductor is a problem due to design or manufacturing constraints, an alternative

method for implementing this function is presented below.

2. Standard ZCD Configuration

The standard configuration for the CS1501 & CS1601 is an auxiliary winding is added to the PFC boost inductor to provide zero-

current detection (ZCD) information.

Figure 1. ZCD Using Auxiliary Winding on PFC Boost Inductor

An auxiliary winding is added to the PFC boost inductor to provide zero-curren t detection (ZCD) information. The ZCD compar-

ator looks for the zero crossing on the au xilia ry winding and switches when th e auxilia ry voltage is be low zero. Switching in t he

valley of the oscillation minimizes the switching losses and reduces EMI noise.

For a full description of ZCD operation , see the CS1501 & CS1601 data sheets.

8 1

Boost Diode

Boost

FET

CS1501

CS1601

GDZCD

IFB

GND

CSIAC

VDD

STBY

rect

link

33 pF

AN356

APR ‘11

AN356REV1

Summary of content (4 pages)

PAGE 1
AN356 Application Note CS1501 & CS1601: DRIVING THE ZCD PIN FROM THE MOSFET DRAIN 1. Introduction The CS1601 is designed with ZCD (zero-current detection), providing the controller with the capability to turn on the MOSFET when the current through the boost inductor is close to zero. This can also be described as valley/zero crossings switching. This is implemented by adding a sense winding on the PFC choke to detect the current.
PAGE 2
AN356 3. Alternative Configuration It is possible to implement ZCD with a resistor divider from the drain of the PFC MOSFET. See Figure 2. Vrect Boost Diode LB R1 47pF 500 V 5 3 V DD ZCD R2 33pF 8 1 VDD IFB CS1501 CS1601 IAC STBY Low Voltage Schottky Vlink 2 GD CS 7 Boost FET 4 GND 6 Rcs Figure 2.
PAGE 3
AN356 Ch 1 - MOSFET Drain Ch 2 - ZCD Pin 5 Ch 3 - Gate Drive Ch 4 - Current in Boost Inductor Figure 3. ZCD Performance — Operation at 100% Load, 108 VAC Ch 1 - MOSFET Drain Ch 2 - ZCD Pin 5 Ch 3 - Gate Drive Ch 4 - Current in Boost Inductor Figure 4. ZCD Performance — Operation at 50% Load, 108 VAC 4. Summary An alternative for ZCD sensing using a resistive divider is presented.
PAGE 4
AN356 5. Revision History Revision Date REV1 APR 2011 Changes Initial Release. Contacting Cirrus Logic Support For all product questions and inquiries contact a Cirrus Logic Sales Representative. To find one nearest you go to http://www.cirrus.com IMPORTANT NOTICE Cirrus Logic, Inc. and its subsidiaries ("Cirrus") believe that the information contained in this document is accurate and reliable.