LD9535 datasheet(10/16 Pages) LEADTREND

10 / 16 page

LD9535

01/08/2019

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD9535-DS-00 January 2019

Application Information

Operation Overview

The LD9535 is built in a multi-mode PWM controller and

integrated a 650V MOSFET. The LD9535 operates a

constant frequency to achieve the CCM as heavy load.

For

demanding

higher

power

efficiency

and

power-saving in light load condition, the LD9535

implements QR function to allow the valley switching

and accomplish zero voltage switching (ZVS). Under

different load conditions, LD9535 provides the different

solutions

for

achieving

higher

efficiency

and

performance.

Under Voltage Lockout (UVLO)

An UVLO comparator is implemented in it to detect the

voltage on the VCC pin. It would assure the supply

voltage enough to turn on the LD9535.

As shown in

Fig. 11, a hysteresis is built in to prevent the shutdown

from the voltage dip during startup.

The turn-on and

turn-off threshold level are set at 16.5V and 7V,

respectively.

Fig. 11

Startup Current and Startup Circuit

The typical startup circuit to generate the LD9535 VCC

is shown in Fig. 12.

During the startup transient, the

VCC is lower than the UVLO threshold thus LD9535 will

not to turn on. Therefore, the current through R1 will

provide the startup current and to charge the capacitor

C1. Whenever the VCC voltage is high enough to turn

on the LD9535 the supply current is provided from the

auxiliary winding of the transformer.

Lower

startup current

requirement

the

PWM

controller will help to increase the value of R1 and then

reduce the power consumption on R1. By using CMOS

process and the special circuit design, the maximum

startup current of LD9535 is only 1

A. If a higher

resistance value of R1 is chosen, it usually takes more

time to start up. To select the value of R1 and C1

carefully will optimize the power consumption and

startup time.

Fig. 12

QR Mode Detection

The transformer will be demagnetized after the main

power MOSFET turns off. A quasi resonant signal will

be detected from auxiliary winding by FB pin through the

external resister.

As soon as the current of the secondary side diode is

down

zero

during

MOSFET-off

period,

the

transformer

’s core is demagnetized completely. VDS of

MOSFET will resonate in discontinuous current mode.

The resonance frequency (FQR) will be obtained as

below.

EMI

Filter

DRAIN

VCC

GND

LD9535

input

Cbulk

Vcc

UVLO(on)

UVLO(off)

I(Vcc)

operating current (~ mA)

startup current

(~µA)

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