MC33368DG datasheet(10/16 Pages) ONSEMI

tên linh kiện	MC33368DG

Giải thích chi tiết về linh kiện	High Voltage GreenLine Power Factor Controller

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MC33368

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10

Table 1. Design Equations

Calculation

Formula

Notes

Converter Output Power

PO + VO IO

Calculate the maximum required output power.

Peak Indicator Current

IL(pk) +

22 PO

h Vac(LL)

Calculated at the minimum required ac line voltage for

output regulation. Let the efficiency η = 0.92 for low line

operation.

Inductance

LP +

t

VO

2

–Vac(LL) h Vac(LL)2

2 VO PO

Let the switching cycle t = 40 ms for universal input (85

to 265 Vac) operation and 20 ms for fixed input (92 to

138 Vac, or 184 to 276 Vac) operation.

Switch On−Time

t(on) +

2PO LP

h Vac2

In theory, the on−time t(on) is constant. In practice, t(on)

tends to increase at the ac line zero crossings due to

the charge on capacitor C5. Let Vac = Vac(LL) for initial

t(on) and t(off) calculations.

Switch Off−Time

t(off) +

t(on)

VO

2 Vac Sin q

–1

The off−time t(off) is greatest at the peak of the ac line

voltage and approaches zero at the ac line zero

crossings. Theta (q) represents the angle of the ac line

voltage.

Minimum Switch

Off−Time

t(off)

min

+

LP IL(pk)

VO

The off−time is at a minimum at ac line crossings. This

equation is used to calculate t(off) as Theta approaches

zero.

Delay Time

td + –R10 C7 ln

VCC –2

VCC

The delay time is used to override the minimum

off−time at the ac line zero crossings by programming

the Frequency Clamp with C7 and R10.

Switching Frequency

f +

1

t(on) ) t(off)

The minimum switching frequency occurs at the peak of

the ac line voltage. As the ac line voltage traverses

from peak to zero, t(off) approaches zero producing an

increase in switching frequency.

Peak Switch Current

R7 +

VCS

IL(pk)

Set the current sense threshold VCS to 1.0 V for

universal input (85 to 265 Vac) operation and to 0.5 V

for fixed input (92 to 138 Vac, or 184 to 276 Vac)

operation. Note that VCS must be less than 1.4 V.

Multiplier Input Voltage

VM +

Vac 2

R5

R3 ) 1

Set the multiplier input voltage VM to 3.0 V at high line.

Empirically adjust VM for the lowest distortion over the

ac line voltage range while guaranteeing startup at

minimum line.

Converter Output

Voltage

VO + Vref

R2

R1 ) 1

–IIB R1

The IIB R1 error term can be minimized with a divider

current in excess of 100 mA.

Converter Output

Peak−to−Peak

Ripple Voltage

DVO(pp) + IL(pk)

1

2 p fac C3

2

) ESR2

The calculated peak−to−peak ripple must be less than

16% of the average dc output voltage to prevent false

tripping of the Overvoltage Comparator. Refer to the

Overvoltage Comparator Text. ESR is the equivalent

series resistance of C3.

Error Amplifier

Bandwidth

BW +

gm

2 p C1

The bandwidth is typically set to 20 Hz. When operating

at high ac line, the value of C1 may need to be

increased.

NOTE: The following converter characteristics must be chosen:

VO = Desired output voltage.

Vac(LL) = AC RMS minimum required operating line voltage for output regulation.

IO = Desired output current.

DVO = Converter output peak−to−peak ripple voltage.

Vac = AC RMS operating line voltage.

Số phần tương tự - MC33368DG

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ON Semiconductor	MC33368DG	276Kb / 16P	High Voltage GreenLine TM Power Factor Controller September, 2005 ??Rev. 8

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