NCP1337 查看數據表（PDF） - ON Semiconductor

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NCP1337

PWM Current−Mode Controller for Free Running Quasi−Resonant Operation

ON Semiconductor 

NCP1337

APPLICATION INFORMATION

INTRODUCTION

The NCP1337 implements a standard current mode

architecture where the switch−off time is dictated by the

peak current setpoint, whereas the core−reset detection

triggers the turn−on event. This component represents

the ideal candidate where low part−count is the key

parameter, particularly in low−cost AC−DC adapters,

consumer electronics, auxiliary supplies, etc. Due to

its high−performance, high−voltage technology, the

NCP1337 incorporates all the necessary features needed to

build a rugged and reliable Switch−Mode Power Supply

(SMPS):

• Quasi−Resonant Operation: Valley−switching

operation is ensured whatever the operating conditions

are, due to the internal soxyless circuitry. As a result,

there are virtually no primary switch turn−on losses,

and no secondary diode recovery losses, and EMI and

video noise perturbations are reduced. The converter

also stays a first−order system and accordingly eases

the feedback loop design.

• Dynamic Self−Supply (DSS): Due to its Very High

Voltage Integrated Circuit (VHVIC) technology,

ON Semiconductor’s NCP1337 allows for a direct pin

connection to the high−voltage DC rail. A dynamic

current source charges up a capacitor and thus

provides a fully independent VCC level. As a result,

low power applications will not require any auxiliary

winding to supply the controller. In applications

where this winding is anyway required (see “Power

Dissipation” section in the application note), the DSS

will simplify the VCC capacitor selection.

• Overcurrent Protection (OCP): When the feedback

current is below minimum value, a fault is detected. If

this fault is present for more than 80 ms, NCP1337

enters an auto−recovery soft burst mode. All pulses are

stopped and the VCC capacitor discharges down to

5.0 V. Then, by monitoring the VCC level, the startup

current source is activated ON and OFF to create a

burst mode. After the current source being activated

twice, the controller tries to restart, with a 4.0 ms

soft−start. If the fault has gone, the SMPS resumes

operation. If the fault is still there, the burst sequence

starts again. The soft−start, together with a minimum

frequency clamp, allow to reduce the noise generated

in the transformer in short−circuit conditions.

• Overvoltage Protection (OVP): By continuously

monitoring the VCC voltage level, the NCP1337 stops

switching whenever an overvoltage condition is

detected.

• Brown−Out Detection (BO): By monitoring the level

on Pin 1 during normal operation, the controller

protects the SMPS against low mains condition. When

Pin 1 level falls below 500 mV, the controller stops

pulsing until this level goes back and resumes

operation. By adjusting the resistor divider connected

between the high input voltage and this pin, start and

stop levels are programmable.

• Over Power Compensation (OPC): An internal

current source injects out of Pin 3 (CS pin) a current

proportional to the voltage applied on Pin 1. As this

voltage is an image of the input voltage, by inserting a

resistor in series with Pin 3, it is possible to create an

offset on the current sense signal that will compensate

the effect of the input voltage variation.

• External Latch Trip Point: By externally forcing a

level on Pin 1 (e.g., with a signal coming from a

temperature sensor) greater than 3.0 V (but below

5.0 V), it is possible to disable the output of the

controller. If the voltage is forced over 5.0 V, the

controller is permanently latched−off: to resume

normal operation, the VCC voltage should go below

4.0 V, which implies to unplug the SMPS from the

mains.

• Standby Ability: Under low load conditions,

NCP1337 enters a Soft−Skip mode: when the CS

setpoint becomes lower than 20% of the maximum

peak current, output pulses are stopped, then switching

is starting again when FB loop forces a setpoint higher

than 25%. As this occurs at low peak current, with

Soft−Skip activated, and as the TOFF is clamped,

noise−free operation is guaranteed, even with a cheap

transformer.

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