LD7516C

08/31/2016

8

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD7516C-DS-01 August 2016

Application Information

Operation Overview

The LD7516C is an excellent primary side feedback

controller with Quasi-Resonant operation to provide high

efficiency. The LD7516C removes the need for secondary

feedback circuits while achieving excellent line and load

regulation. It meets the green-power requirement and is

intended for the use in those modern switching power

suppliers and linear adaptors that demand higher power

efficiency and power-saving. It integrates with more

functions to reduce the external components counts and

the size. Major features are described as below.

Under Voltage Lockout (UVLO)

An UVLO comparator is implemented in it to detect the

voltage across VCC pin. It would assure the supply

voltage enough to turn on the LD7516C and further to

drive the power MOS.

As shown in Fig. 11, a hysteresis

is built in to prevent shutdown from voltage dip during

startup.

Vcc

UVLO(on)

UVLO(off)

t

t

I(Vcc)

operating current

(~ mA)

startup current

(~µA)

Fig. 11

Startup Current and Startup Circuit

The typical startup circuit to generate VCC of the

LD7516C is shown in Fig. 12. At startup transient, the

VCC is below the UVLO(on) threshold, so there

’s no pulse

delivered out from LD7516C to drive the power MOS.

Therefore, the current through R1 will be used to charge

the capacitor C1. Until the VCC is fully charged to deliver

the

drive-out

signal,

the

auxiliary

winding

of

the

transformer will provide supply current.

Lower startup

current requirement on the PWM controller will help to

increase the value of R1 and then reduce the power

consumption on R1. By using CMOS process and some

unique circuit design, the LD7516C requires only 1.9

A

max to start up. Higher resistance of R1 will spend much

more time to start up. The user is recommended to select

proper value of R1 and C1 to optimize the power

consumption and startup time.

EMI

Filter

R1

OUT

CS

VCC

GND

LD7516C

AC

Input

C1

Cbulk

D1

Fig. 12