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P1014AP100G

Self-Supplied Monolithic Switcher for Low Standby Power Offline SMPS

ON Semiconductor 

NCP1010, NCP1011, NCP1012, NCP1013, NCP1014

APPLICATION INFORMATION

Introduction

The NCP101X 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 on Page 2, details the differences between

references, mainly peak current setpoints and 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 of

a 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.

Fail−safe optocoupler and OVP: When an auxiliary

winding is connected to the VCC pin, the device stops its

internal Dynamic Self−Supply and takes its operating power

from the auxiliary winding. A 8.7 V active clamp is

connected between VCC and ground. In case the current

injected in this clamp exceeds a level of 7.4 mA (typical),

the controller immediately latches off and stays in this

position until VCC cycles down to 3.0 V (e.g. unplugging the

converter from the wall). By adjusting a limiting resistor in

series with the VCC terminal, it becomes possible to

implement an overvoltage protection function, latching off

the circuit in case of broken optocoupler or feedback loop

problems.

Low standby−power: If SMPS naturally exhibits a good

efficiency at nominal load, it begins to be less efficient when

the output power demand diminishes. By skipping unneeded

switching cycles, the NCP101X 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 7.0 W universal power supply.

No acoustic noise while operating: Instead of skipping

cycles at high peak currents, the NCP101X waits until the

peak current demand falls below a fixed 1/4 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 close the loop. Ready−to−use

templates can be downloaded in OrCAD’s PSpice, and

INTUSOFT’s IsSpice4 from ON Semiconductor web site,

NCP101X related section.

Dynamic Self−Supply

When the power supply is first powered from the mains

outlet, the internal current source (typically 8.0 mA) is

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

Once the voltage on this VCC capacitor reaches the VCCOFF

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 13 details the

internal circuitry.

Vref OFF = 8.5 V

Vref ON = 7.5 V

Vref Latch = 4.7 V*

Drain

+

-

Startup Source

Internal Supply

VCC

+

Vref

VCCOFF

+200 mV

(8.7 V Typ.)

*In fault condition

+

CVCC

Figure 13. The Current Source Regulates VCC

by Introducing a Ripple

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