RT7310

Copyright © 2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS7310-00

October

2014

www.richtek.com

3

Function Block Diagram

COMP

GD

GND

13V

Gate

Driver

CS

ZCD

Output OVP

OTP

PWM

Clamping

Circuit

Under-

Voltage

Lockout

(16V/9V)

VDD

Over-Voltage

Protection

UVLO

VDD OVP

VDD

PWM

Control

Logic

Valley

Detector

Valley Signal

Constant Current

with Phase-Cut

Dimming Control

Output

Over-Voltage

Protection

Over-

Temperature

Protection

Leading-

Edge

Blanking

Starter

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



+

-

Q1

TX1

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.

Peak Inductor Current

MOSFET Current

Input Voltage

Average Input Current

Output Diode Current

Figure 2. Inductor Current of CRM with Constant

On-Time Control