LD7535A Ver la hoja de datos (PDF) - Unspecified

Número de pieza

componentes Descripción

Fabricante

LD7535A

Green-Mode PWM Controller

Unspecified 

LD7535/LD7535A

Fig. 15

A 350nS leading-edge blanking (LEB) time is included in the

input of CS pin to prevent the false-trigger from the current

spike. In the low power application, if the total pulse width of

the turn-on spikes is less than 350nS and the negative spike

on the CS pin doesn’t exceed -0.3V, it could eliminated the

R-C filter (as shown in the figure16).

However, the total pulse width of the turn-on spike is

decided by the output power, circuit design and PCB layout.

It is strongly recommended to adopt a smaller R-C filter (as

shown in figure 17) for higher power application to avoid the

CS pin being damaged by the negative turn-on spike.

Fig. 16

Output Stage and Maximum Duty-Cycle

An output stage of a CMOS buffer, with typical 300mA

driving capability, is incorporated to drive a power MOSFET

directly. And the maximum duty-cycle of LD7535/LD7535A

is limited to 75% to avoid the transformer saturation.

Oscillator and Switching Frequency

Connect a resistor from RT pin to GND according to the

equation below to program the normal switching frequency:

fSW

=

65.0

RT(KΩ )

× 100(KHz)

Fig. 17

The operating frequency range for the LD7535/LD7535A is

recommended to set between 50KHz and 130KHz.

Voltage Feedback Loop

The voltage feedback signal is provided from the TL431 at

the secondary side through the photo-coupler to the COMP

pin of the LD7535/LD7535A. Similar to UC3842, the

LD7535/LD7535A would carry 2 diodes voltage offset at the

stage to feed the voltage divider at the ratio of 1/3, that is,

10

Leadtrend Technology Corporation www.leadtrend.com.tw

LD7535&LD7535A-DS-01c December 2007

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