AP3790 datasheet(6/17 Pages) DIODES

6 / 17 page

AP3790

Document number: DS37221 Rev. 3 - 2

6 of 17

www.diodes.com

October 2014

AP3790

A Product Line of

Diodes Incorporated

Operation Principle Description

FR1

TR1

R13

OUT

VCC

R14

AP3790

CPC

GND

5V/1A

D4~D7

R12

R11

R10

Figure 1. 7.5W Battery Charger

Figure 1 is the typical application circuit of AP3790, which is a conventional Flyback converter with a 3-winding transformer---primary winding (NP),

secondary winding (NS) and auxiliary winding (NAUX). The auxiliary winding is used for providing VCC supply voltage for IC and sensing the output

voltage feedback signal to FB pin.

Figure 2 shows the typical waveforms which demonstrate the basic operating principle of AP3790 application. And the parameters are defined as

following.

IP---The primary side current

IS ---The secondary side current

IPK---Peak value of primary side current

IPKS---Peak value of secondary side current

VSEC---The transient voltage at secondary winding

VS---The stable voltage at secondary winding when rectification diode is in conducting status, which equals the sum of output voltage VOUT and

the forward voltage drop of diode

VAUX---The transient voltage at auxiliary winding

VA--- The stable voltage at auxiliary winding when rectification diode is in conducting status, which equals the sum of voltage VCC and the forward

voltage drop of auxiliary diode

tSW ---The period of switching frequency

tONP ---The conduction time when primary side switch is “ON”

tONS ---The conduction time when secondary side diode is “ON”

tOFF ---The dead time when neither primary side switch nor secondary side diode is “ON”

tOFFS --- The time when secondary side diode is “OFF”

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