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NCP1607

Cost Effective Power Factor Controller

ON Semiconductor 

NCP1607

Introduction

The NCP1607 is a voltage mode power factor correction

(PFC) controller designed to drive cost effective

pre−converters to meet input line harmonic regulations.

This controller operates in critical conduction mode

(CRM) for optimal performance in applications up to

250 W. Its voltage mode scheme enables it to obtain unity

power factor without the need for a line sensing network.

The output voltage is accurately controlled by a high

precision error amplifier. The controller also implements a

comprehensive array of safety features for robust designs.

The key features of the NCP1607 are as follows:

• Constant on time (Voltage Mode) CRM operation.

High power factor ratios are easily obtained without

the need for input voltage sensing. This allows for

optimal standby power consumption.

• Accurate and Programmable On Time Limitation. The

NCP1607 uses an accurate current source and an

external capacitor to generate the on time.

• High Precision Voltage Reference. The error amplifier

reference voltage is guaranteed at 2.5 V ±1.6% over

process, temperature, and voltage supply levels. This

results in very accurate output voltages.

• Very Low Startup Current Consumption. The circuit

consumption is reduced to a minimum (< 40 mA)

during the startup phase, allowing fast, low loss,

charging of VCC. The architecture of the NCP1607

gives a controlled undervoltage lockout level and

provides ample VCC hysteresis during startup.

• Powerful Output Driver. A Source 500 mA / Sink

800 mA totem pole gate driver is used to provide rapid

turn on and turn off times. This allows for improved

efficiencies and the ability to drive higher power

MOSFETs. Additionally, a combination of active and

passive circuitry is used to ensure that the driver

output voltage does not float high while VCC is below

its turn on level.

• Programmable Overvoltage Protection (OVP). The

adjustable OVP feature protects the PFC stage against

excessive output overshoots that could damage the

application. These events can typically occur during

the startup phase or when the load is abruptly

removed.

• Protection against Open Feedback Loop

(Undervoltage Protection). Undervoltage protection

(UVP) disables the PFC stage when the output voltage

is excessively low. This also protects the circuit in

case of a failure in the feedback network: if no voltage

is applied to FB because of a poor connection or if the

FB pin is floating, UVP is activated shutting down the

converter.

• Overcurrent Limitation. The peak current is accurately

limited on a pulse by pulse basis. The level is

adjustable by modifying the current sense resistor. An

integrated LEB filter reduces the chance of noise

prematurely triggering the overcurrent limit.

• Shutdown Features. The PFC pre−converter is placed

in a shutdown mode by grounding the FB pin or the

ZCD pin. During this mode, the ICC current

consumption is reduced and the error amplifier is

disabled.

Application information

Most electronic ballasts and switching power supplies

use a diode bridge rectifier and a bulk storage capacitor to

produce a dc voltage from the utility ac line (Figure 20).

This DC voltage is then processed by additional circuitry

to drive the desired output.

Rectifiers

Converter

AC

Line

+ Bulk

Storage

Load

Capacitor

Figure 20. Typical Circuit without PFC

This simple rectifying circuit draws power from the line

when the instantaneous ac voltage exceeds the capacitor

voltage. Since this occurs near the line voltage peak, the

resulting current draw is non sinusoidal and contains a very

high harmonic content. This results in a poor power factor

(typically < 0.6) and consequently, the apparent input

power is much higher than the real power delivered to the

load. Additionally, if multiple devices are tied to the same

input line, the effect is magnified and a “line sag” effect can

be produced (see Figure 21).

Vpk

Rectified DC

0

Line

Sag

AC Line Voltage

0

AC Line Current

Figure 21. Typical Line Waveforms without PFC

Increasingly, government regulations and utility

requirements necessitate control over the line current

harmonic content. To meet this need, power factor

correction is implemented with either a passive or active

circuit. Passive circuits usually contain a combination of

large capacitors, inductors, and rectifiers that operate at the

ac line frequency. Active circuits incorporate some form of

a high frequency switching converter that regulates the

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