ACT36X datasheet(12/22 Pages) ACTIVE-SEMI

12 / 22 page

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PSR

PSR TM

Active

High Efficiency AC/DC Primary Switching Solutions

ACT334 5V/700MA CHARGER

Operation and Application

Figure 1 is the schematic of an offline charger

using ACT334 to provide output power of

5V/700mA. This circuit is a typical flyback power

supply which includes the AC rectified circuit

(D1,D2,D3,D4,C1,L1, C2),power drive circuit (BD

pin, Q1), secondary rectified circuit (D8, C5,C6)

and the IC control circuit. ACT334 is a Primary

Side Regulator (PSR) so that the power supply

unit can regulate current and voltage without

Opto-coupler. Pin 4 and Pin 2 are the VDD and

ground pins to provide power for the IC. Pin 3 is

the base drive for the NPN transistor. Pin 1 is the

switching pin. Pin 5 is the feedback pin that

senses the output current and output voltage. Pin

6 is the peak current sense pin. Resistance of

R10 determines the output DC cord compensa-

tion percentage.

This circuit can be used as universal charger for

Cell Phones, PDAs, MP3,Portable Media Play-

ers, DSCs, and Other Portable Devices and Ap-

pliances.

Key Component Selection

The maximum output current is decided by for-

mula(1).

Lp is the transformer inductance value, Rcs is the

current sense resistor, which is shown as R9 in

the schematic. Fsw is the switching frequency,

which design value is 75kHz. η is the overall sys-

tem efficiency, which value is approximately

equal to 70%. Voutcc is the output voltage, which

setting is through the flyback voltage of auxiliary

winding and the feedback resistor R5, R6 as

shown in formula (2).

Np/Ns/Naux (147/9/24) must be designed cor-

rectly to ensure it operates in DCM in all condi-

tions. A design value Voutcc equal to 5V and

Ioutcc_min equal to 700mA are used to do the

design. Ns and Naux are number of turns of sec-

ondary and auxiliary of the transformer. VSEC_R

is the forward voltage drop of the output rectifier

diode at approximately 0.1A bias. The peak cur-

rent limit is set by (0.396×0.9)/Rcs

)

(

)

396

(

OUTCC

SEC

AUX

REF

OUTCC

)

(

−

Input Voltage

Device

Standby Power

Output Voltage

Power output

Transformer

Topology

85-264VAC

ACT334

30mW

3.5W

EPC13

Flyback

Figure 1:

Schematic of Charger

L=41.3mm

W=28.1mm

H=13.2mm

(1)

(2)

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