NCP1654BD200R2G 查看數據表（PDF） - ON Semiconductor

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NCP1654BD200R2G

Power Factor Controller for Compact and Robust, Continuous Conduction Mode Pre-Converters

ON Semiconductor 

NCP1654

Input and output power (Pin and Pout) are derived in (Equation 15) when the circuit efficiency η is obtained or assumed.

The variable Vac stands for the rms input voltage.

Pin

+

Vac 2

Zin

+

2pRCS

@

(Vcontrol * VCONTROL(min))

Ǹ2 RMRSENSEVoutKBO

@

VREF

@

Vac

(eq. 15)

T

(Vcontrol

*

V

CONTROL(min))Vac

Vout

Pout + h Pin + h

2pRCS @ (Vcontrol * VCONTROL(min)) @ VREF @ Vac

Ǹ2 RMRSENSEVoutKBO

(eq. 16)

T

(Vcontrol

*

V

CONTROL(min))Vac

Vout

Follower Boost

The “Follower Boost” is an operation mode where the

pre−converter output voltage stabilizes at a level that varies

linearly versus the ac line amplitude. This technique aims

at reducing the gap between the output and input voltages

to optimize the boost efficiency and minimize the cost of

the PFC stage (refer to MC33260 data sheet for more

details at http://www.onsemi.com ).

The NCP1654 operates in follower boost mode when

Vcontrol is constant, i.e. Vcontrol raises to its maximum value

VCONTROL(max). Re−formulate (Equation 16) to become

(Equation 17) and (Equation 18) by replace Vcontrol by

VCONTROL(max). If Vcontrol is constant based on

(Equation 15), for a constant load or power demand the

output voltage Vout of the converter is proportional to the

rms input voltage Vac. It means the output voltage Vout

becomes lower when the rms input voltage Vac becomes

lower. On the other hand, the output voltage Vout becomes

lower when the load or power demand becomes higher.

Pout

+

h

2pRCS

@

(VCONTROL(max) * VCONTROL(min))

Ǹ2 RMRSENSEVoutKBO

@

VREF

@

Vac

(eq. 17)

+

h

2pRCS @

Ǹ2

DVCONTROL @ VREF

RMRSENSEVoutKBO

@

Vac

Vout

+

h

2pRCS @ DVCONTROL @ VREF

Ǹ2 RMRSENSEKBO

@

Vac

Pout

(eq. 18)

where

VCONTROL(max) is the maximum control voltage.

DVCONTROL is the gap between VCONTROL(max) and

VCONTROL(min).

It is illustrated in Figure 39.

the output voltage Vout will always be higher than the input

voltage Vin even though Vout is reduced in follower boost

operation. As a result, the on time t1 is reduced. Reduction

of on time makes the loss of the inductor and power

MOSFET smaller. Hence, it allows cheaper cost in the

inductor and power MOSFET or allows the circuit

components to operate at a lower stress condition in most

Vout (Traditional Boost)

of the time.

Vout (Follower Boost)

Vin

Time

Pout

Time

Figure 39. Follower Boost Characteristics

Follower Boost Benefits

The follower boost circuit offers and opportunity to

reduce the output voltage Vout whenever the rms input

voltage Vac is lower or the power demand Pout is higher.

Because of the step−up characteristics of boost converter,

Reference Section

The internal reference voltage (VREF) is trimmed to be

±2% accurate over the temperature range (the typical value

is 2.5 V). VREF is the reference used for the regulation.

VREF also serves to build the thresholds of the fast transient

response, Overvoltage (OVP), brown out (BO), and

Undervoltage protections (UVP).

Output Feedback

The output voltage Vout of the PFC circuits is sensed at

Vfb pin via the resistor divider (RfbL and RfbU) as shown in

Figure 38. Vout is regulated as described in (Equation 19).

Vout

+

VREF

RfbU ) RfbL

RfbL

(eq. 19)

http://onsemi.com

16

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