C2474 datasheet, PDF - EEWORLD Datasheet

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C2474: Description2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR; CategoryPassive components; File Size461KB，18 Pages; ManufacturerETC2

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C2474 Overview

2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR

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C2472, C2473 and C2474 Datasheet

RDFC Controllers for Offline Applications

ADVANTAGES



Low system component count

High average efficiency

Low standby power consumption

EMI compliance without extra components

High isolation & surge voltage withstand

High power density in very small size

C2474PW1

PDIP-8

C2472PX2

SOT23-6

FEATURES



Highly integrated CMOS controller IC

Low cost package options

Drive suitable for low cost bipolar power transistors

Resonant switching for high efficiency and low EMI

Frequency optimised for power circuit parasitics

Protection against overload, over-temperature and under-voltage

C2473PX1

SOP-8

APPLICATIONS

External AC/DC charger/adaptor (single voltage input) e.g. cordless phones, portable electric tools.

Embedded PSU (single voltage input) e.g. set-top boxes, DVD players, audio products, domestic appliances.

OVERVIEW

The C2472, C2473 and C2474 controllers use CamSemi’s Resonant Discontinuous Forward Converter

(RDFC) topology to create a high efficiency, low cost alternative to line-frequency transformer PSUs. By

operating in resonant mode, EMI is greatly reduced, enabling the replacement of linear PSUs in demanding

applications such as audio products and cordless phone chargers. The C2472, C2473 and C2474 controllers

also offer overload protection which is usually associated with more expensive switch mode solutions.

VDD

Vdd

regulator

AUX

Switch

saturation

sensing

COL

Resonance

sensing

Base

drive

Current

sensing

RDFC

Control

BAS

GND

Figure 1: Block Diagram of the C2472, C2473 and C2474 Controller ICs

Product data

Page 1 of 18

DS-1423-0709C

26-Sep-2007

C2472, C2473 and C2474

Datasheet

RDFC Controllers for Offline Applications

Start-up and Active State Power Conversion Modes

In the Start-up and Active states the C2472, C2473 and C2474 ICs have several modes for controlling power

conversion that are designed to achieve maximum efficiency and to limit power (current) across a wide range

of loads. Refer to Table 2 for a summary of each mode.

Mode

Standby

Typical Load

Range

OUT

≥ 0% to

~20% of rated

current

Description

Standby mode reduces power consumption at low loads. It achieves this by

progressively reducing the on-time then by increasing the off-time as the load

decreases. As load increases, the converter duty is increased until the controller

returns to Normal mode. Typically, mains ripple causes change of operating mode

during each mains half-cycle, with the converter moving to lower-power modes

between peaks of the mains voltage.

Normal mode is used for steady state power delivery. During Normal mode the power

device switches in a fully resonant minimum-voltage-switching waveform, with the off-

time determined by the transformer resonance (T

RES

) and the on-time being equal to

75% of the off time. A low level of primary switch current, sensed via the CS pin

voltage, causes the controller to change to Standby mode and a high level to Overload

mode.

Overload mode is activated at high output loads. In this mode the on-time of the

primary switch is terminated early (before 75% of T

RES

) when the primary current

exceeds a preset maximum, thereby protecting the primary switch and limiting the

output current. This results in reduction of the output voltage. Heavy overload (sensed

by the on-period of the primary switch reducing below a preset time) causes Foldback

mode to be entered.

Foldback mode is entered from the Overload mode. In this mode the controller reduces

the on/off duty cycle to protect the power supply and any connected load by both

shortening the on-period and increasing the off-period of the primary switch. Converter

cycles continue to maintain auxiliary power to the controller. The controller exits the

Foldback mode and enters the Power Burst mode after a fixed number of power

conversion cycles.

Power Burst mode is entered periodically from Foldback mode in order to restart the

power supply output. In Power Burst mode, the controller operates at maximum

delivered power for a set number of power converter cycles. At the end of the burst, if

the load is not excessive, the converter goes to Normal mode; otherwise it reverts to

Foldback mode.

Normal

OUT

> ~20% to

100% of rated

current

Overload

OUT

>~100%

rated current

Foldback

OUT

< ~70%

rated output

Power

Burst

OUT

< ~70%

rated output

Table 2: Summary of Active Operating Modes

When the controller goes from Sleep to Start-up state, its power conversion mode is set to Standby. Typically

the converter output voltage is low at this time so the primary switch current is high during the first few

converter cycles. This causes the operating mode to change quickly to Normal or Overload mode.

Product data

Page 5 of 18

DS-1423-0709C

26-Sep-2007

C2474 Related Products

	C2474	C2472	C2472PX2-TR13	C2472PX2-TR7	C2473	C2473PX1-TR13	C2473PX1-TR7	C2474PW1-T1
Description	2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR	2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR	2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR	2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR	2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR	2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR	2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR	2 ELEMENT, 340 uH, GENERAL PURPOSE INDUCTOR

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