MC33368 View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

MFG CO.

MC33368

HIGH VOLTAGE GREENLINE POWER FACTOR CONTROLLER

Motorola => Freescale 

MC33368

Table 1. Design Equations

Calculation

Converter Output Power

Peak Indicator Current

Inductance

Switch On–Time

Switch Off–Time

Formula

+ PO VO IO

+ Ǹ IL(pk)

2 2 PO

h Vac(LL)

ǒ Ǔ Ǹ t

VO

2

–Vac(LL)

h Vac(LL)2

+ Ǹ LP

2 VO PO

+ t(on)

2 PO LP

h Vac2

+ Ǹ Ť Ť t(off)

t(on)

VO

2 Vac Sin q

–1

Notes

Calculate the maximum required output power.

Calculated at the minimum required ac line voltage for

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

operation.

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

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

138 Vac, or 184 to 276 Vac) operation.

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.

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 (θ) represents the angle of the ac line voltage.

Minimum Switch

Off–Time

Delay Time

Switching Frequency

+ t(off)min

LP IL(pk)

VO

+ ǒ Ǔ td

– R10 C7 ln

VCC – 2

VCC

+ ) f

1

t(on) t(off)

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

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

zero.

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.

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

Multiplier Input Voltage

Converter Output

Voltage

Converter Output

Peak–to–Peak

Ripple Voltage

+ R7

VCS

IL(pk)

ǒ Ǔ + )Ǹ VM

Vac 2

R5

R3

1

ǒ Ǔ + ) VO

Vref

R2

R1

1 – IIB R1

Ǹǒ Ǔ + DVO(pp) IL(pk)

2

) 1

2 p fac C3

ESR2

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.

Set the mulltiplier 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.

The IIB R1 error term can be minimized with a divider

current in excess of 100 µA.

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.

IO = Desired output current.

Vac = AC RMS operating line voltage.

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

∆VO = Converter output peak–to–peak ripple voltage.

10

MOTOROLA ANALOG IC DEVICE DATA

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