ACT36X datasheet(18/22 Pages) ACTIVE-SEMI

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-18-

PSR

PSR TM

Active

High Efficiency AC/DC Primary Switching Solutions

ACT337 5V/1500MA CHARGER

Operation and Application

Figure 1 is the schematic of an offline charger

using ACT337 to provide output power of

5V/1500mA. This circuit is a typical flyback power

supply which includes the AC rectified circuit

(BD1,C1, L2,C2),power drive circuit (BD pin, Q1),

secondary rectified circuit (D8, C5,C6) and the IC

control circuit. ACT337 is a Primary Side Regula-

tor (PSR) so that the power supply unit can regu-

late current and voltage without Opto-coupler.

Pin 6 and Pin 2,4,7 are the VDD and ground pins

to provide power for the IC. Pin 8 is the base

drive for the NPN transistor. Pin 1 is the switch-

ing pin. Pin 5 is the feedback pin that senses the

output current and output voltage. Pin 3 is the

peak current sense pin. Resistance of R10 deter-

mines the output DC cord compensation percent-

age.

This circuit can be used as universal charger for

Cell Phones, PDAs, MP3,Portable Media Play-

ers, Shaver, DSCs, and Other Portable Devices

and Appliances.

Key Component Selection

Input Voltage

Device

Standby Power

Output Voltage

Power output

Transformer

Topology

85-264VAC

ACT337

30mW

7.5W

EE16

Flyback

Figure 1:

Schematic of Charger

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 fre-

quency, which design value is 75kHz.η is the

overall system efficiency,which value is approxi-

mately equal to 70%. Voutcc is the output volt-

age, which setting is through the flyback voltage

of auxiliary winding and the feedback resistor

R5,

shown

formula

(2).

Np/Ns/Naux (110/8/18) 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 1500mA are used to do the

design. Ns and Naux are number of turns of

secondary and auxiliary of the transformer.

VSEC_R is the forward voltage drop of the out-

put rectifier diode at approximately 0.1A bias.

The peak current limit is set by (0.396×0.9)/Rcs.

)

(

)

396

(

OUTCC

SEC

AUX

REF

OUTCC

)

(

−

L=50.6mm

W=26.2mm

H=20.9mm

(1)

(2)

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