NCP1653, NCP1653A

http://onsemi.com

9

FUNCTIONAL DESCRIPTION

Introduction

The NCP1653 is a Power Factor Correction (PFC) boost

controller

designed

to

operate

in

fixed−frequency

Continuous Conduction Mode (CCM). It can operate in

either peak current−mode or average current−mode.

Fixed−frequency operation eases the compliance with

EMI standards and the limitation of the possible radiated

noise that may pollute surrounding systems. The CCM

operation reduces the application di/dt and the resulting

interference. The NCP1653 is designed in a compact 8−pin

package which offers the minimum number of external

components. It simplifies the design and reduces the cost.

The output stage of the NCP1653 incorporates

±1.5 A

current capability for direct driving of the MOSFET in

high−power applications.

The NCP1653 is implemented in constant output voltage

or follower boost modes. The follower boost mode permits

one to significantly reduce the size of the PFC circuit

inductor and power MOSFET. With this technique, the

output voltage is not set at a constant level but depends on

the RMS input voltage or load demand. It allows lower

output voltage and hence the inductor and power MOSFET

size or cost are reduced.

Hence, NCP1653 is an ideal candidate in high−power

applications where cost−effectiveness, reliability and high

power factor are the key parameters. The NCP1653

incorporates all the necessary features to build a compact

and rugged PFC stage.

The NCP1653 provides the following protection features:

1. Overvoltage Protection (OVP) is activated and

the Drive Output (Pin 7) goes low when the

output voltage exceeds 107% of the nominal

regulation level which is a user−defined value.

The circuit automatically resumes operation when

the output voltage becomes lower than the 107%.

2. Undervoltage Protection (UVP) is activated and

the device is shut down when the output voltage

goes below 8% of the nominal regulation level.

The circuit automatically starts operation when

the output voltage goes above 12% of the

nominal regulation level. This feature also

provides output open−loop protection, and an

external shutdown feature.

3. Overpower Limitation (OPL) is activated and the

Drive Output (Pin 7) duty ratio is reduced by

pulling down an internal signal when a computed

input power exceeds a permissible level. OPL is

automatically deactivated when this computed input

power becomes lower than the permissible level.

4. Overcurrent Protection (OCP) is activated and

the Drive Output (Pin 7) goes low when the

inductor current exceeds a user−defined value.

The operation resumes when the inductor current

becomes lower than this value.

5. Thermal Shutdown (TSD) is activated and the

Drive Output (Pin 7) is disabled when the

junction temperature exceeds 150

_C. The

operation resumes when the junction temperature

falls down by typical 30

_C.

CCM PFC Boost

A CCM PFC boost converter is shown in Figure 25. The

input voltage is a rectified 50 or 60 Hz sinusoidal signal.

The MOSFET is switching at a high frequency (typically

basically consists of high and low−frequency components.

capacitor in order to eliminate the high−frequency

cannot be too bulky because it can pollute the power factor

by distorting the rectified sinusoidal input voltage.

Figure 25. CCM PFC Boost Converter

L

PFC Methodology

The NCP1653 uses a proprietary PFC methodology

particularly designed for CCM operation. The PFC

methodology is described in this section.

Figure 26. Inductor Current in CCM

I

in

t 2

t 1

time

T

I L

switching period T includes a charging phase for duration

conversion ratio is obtained in (eq.1).

Vout

Vin

+

t1 ) t2

t2

+

T

T

* t1

Vin +

T

* t1

T

Vout

(eq.1)