NCP1631 Ver la hoja de datos (PDF) - ON Semiconductor

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Fabricante

NCP1631

Interleaved, 2-Phase Power Factor Controller

ON Semiconductor 

NCP1631

Figure 12. Zero Current Detection Timing Diagram

(VAUX is the Voltage Provided by the ZCD Winding)

Current Sense

The NCP1631 is designed to monitor a negative voltage

proportional to total input current, i.e., the current drawn by

the two interleaved branches (Iin). As portrayed by

Figure 13, a current sense resistor (RCS) is practically

inserted within the return path to generate a negative

voltage (VCS) proportional to Iin. The circuit uses VCS to

detect when Iin exceeds its maximum permissible level. To

do so, the circuit incorporates an operational amplifier that

sources the current necessary to maintain the CS pin

voltage null (refer to Figure 13). By inserting a resistor

ROCP between the CS pin and RCS, we adjust the current

that is sourced by the CS pin (ICS) as follows:

* [RCSICOIL] ) [ROCPICS] + 0

(eq. 10)

Which leads to:

ICS

+

RCS

ROCP

ICOIL

(eq. 11)

In other words, the pin 9 current (ICS) is proportional to

the coil current.

A negative clamp protects the circuit from the possible

negative voltage that can be applied to the pin. This

protection is permanently active (even if the circuit off).

The clamp is designed to sustain 5 mA. It is recommended

not to sink more than 5 mA from the CS pin for a proper

operation.

Two functions use ICS: the over current protection and

the in−rush current detection.

Over−Current Protection (OCP)

If ICS exceeds IILIM1 (210 mA typical), an over−current

is detected and the on−time is decreased proportionally to

the difference between the sensed current IIN and the

210 mA OCP threshold.

The on−time reduction is done by injecting a current Ineg

in the negative input of the “VTON processing circuit”

OPAMP. (See Figure 7)

Ineg + 0.5(ICS * 210 m)

(eq. 12)

This current is injected each time the OCP signal is high.

The maximum coil current is:

ICOIL(max)

+

ROCP

RCS

IILIM1

(eq. 13)

In−rush Current Detection

When the PFC stage is plugged to the mains, the bulk

capacitor is abruptly charged to the line voltage. The

charge current (named in−rush current) can be very huge

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