RT7306

Copyright © 2015 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS7306-00

July

2015

www.richtek.com

3

Function Block Diagram

COMP

GD

GND

13V

Gate

Driver

Ramp

Generator

CS

ZCD

Output OVP

OTP

PWM

Clamping

Circuit

Under-Voltage

Lockout

(16V/9V)

VDD

Over-Voltage

Protection

UVLO

VDD OVP

VDD

PWM

Control

Logic

Current-Limit

Comparator

1.2V

Valley

Detector

Valley Signal

Constant

Current

Control

Constant on-Time

Comparator

Output

Over-Voltage

Protection

Over-

Temperature

Protection

Leading

Edge

Blanking

Output Diode

Short-Circuit

Protection

Starter

Circuit

+

-

+

-

THD

Optimizer

Feed-Forward

Compensator

HV Start-Up

Control

HV

Dimming

Control

DIM

Operation

Critical-Conduction Mode (CRM) with Constant

On-Time Control

Figure 1 shows a typical flyback converter with input

following equation :

IN

L_PK

ON

m

V

It

L



TX1

Q1

+

-

Figure 1. Typical Flyback Converter

If the input voltage is the output voltage of the

full-bridge

rectifier

with

sinusoidal

input

voltage

expressed as the following equation :

IN_PK

ON

L_PK

m

V

sin(

θ)t

I

L





When the converter operates in CRM with constant

on-time control, the envelope of the peak inductor

current will follow the input voltage waveform with

in-phase. Thus, high power factor can be achieved, as

shown in Figure 2.