NCP1015 데이터 시트보기 (PDF) - ON Semiconductor

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NCP1015

Self-Supplied Monolithic Switcher for Low Standby Power Offline SMPS

ON Semiconductor 

NCP1015

APPLICATION INFORMATION

Introduction

The NCP1015 offers a complete current−mode control

solution (actually an enhanced NCP1200 controller section)

together with a high−voltage power MOSFET in a

monolithic structure. The component integrates everything

needed to build a rugged and low−cost Switch−Mode Power

Supply (SMPS) featuring low standby power. The quick

selection table details the differences in operating

frequency.

• No need for an auxiliary winding: ON Semiconductor

Very High Voltage Integrated Circuit technology lets

you supply the IC directly from the high−voltage dc

rail. We call it Dynamic Self−Supply (DSS). This

solution simplifies the transformer design and ensures a

better control of the SMPS in difficult output

conditions, e.g. constant current operations. However,

for improved standby performance, an auxiliary

winding can be connected to the VCC pin to disable the

DSS operation.

• Short−circuit protection: by permanently monitoring

the feedback line activity, the IC is able to detect the

presence short−circuit, immediately reducing the output

power for a total system protection. Once the short has

disappeared, the controller resumes and goes back to

normal operation.

• Low standby−power: If SMPS naturally exhibit a good

efficiency at nominal load, they begin to be less

efficient when the output power demand diminishes. By

skipping un−needed switching cycles, the NCP1015

drastically reduces the power wasted during light load

conditions. An auxiliary winding can further help

decreasing the standby power to extremely low levels

by invalidating the DSS operation. Typical

measurements show results below 80 mW @ 230 Vac

for a typical 7 W universal power supply.

• No acoustic noise while operating: Instead of skipping

cycles at high peak currents, the NCP1015 waits until

the peak current demand falls below a fixed 0.25 of the

maximum limit. As a result, cycle skipping can take

place without having a singing transformer. You can

thus select cheap magnetic components free of noise

problems.

• SPICE model: a dedicated model to run transient

cycle−by−cycle simulations is available but also an

averaged version to help you closing the loop.

Ready−to−use templates can be downloaded in

OrCAD’s PSpice, and INTUSOFT’s IsSpice4 from ON

Semiconductor web site, NCP1015 related section.

Dynamic Self−Supply

When the power supply is first powered from the mains

outlet, the internal current source (typically 8 mA) is biased

and charges up the VCC capacitor from the drain pin. Once

the voltage on this VCC capacitor reaches the VCC(off) level

(typically 8.5 V), the current source turns off and pulses are

delivered by the output stage: the circuit is awake and

activates the power MOSFET. Figure 12 details the internal

circuitry:

Vref OFF = 8.5 V

Vref ON = 7.5 V

VrefLatch = 4.7 V

Drain

+

-

Startup Source

Internal Supply

VCC

+

Vref

VCC(off)

+200 mV

(8.7 V Typ.)

+

CVCC

Figure 12. The Current Source Regulates VCC

by Introducing a Ripple

Being loaded by the circuit consumption, the voltage on

the VCC capacitor goes down. When the DSS controller

detects that VCC has reached 7.5 V (VCC(on)), it activates the

internal current source to bring VCC toward 8.5 V and stops

again: a cycle takes place whose low frequency depends on

the VCC capacitor and the IC consumption. A 1 V ripple

takes place on the VCC pin whose average value equals

(VCC(off) + VCC(on)) / 2. Figure 13 shows a typical operation

of the DSS.

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