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TK75005MCMG

LOW-COST FLEXIBLE PWM CONTROLLER

Toko America Inc  

TK75005

APPLICATIONS INFORMATION

BOOST POWER FACTOR CORRECTOR APPLICATION

CIRCUIT

Figure 7 shows a universal-input, 100 W boost power

factor corrector application circuit. The control technique is

called “current-clamped control.” Both the control technique

and the application circuit with waveforms are described in

the paper “Low-Cost Power Factor Correction/Line-

Harmonics Reduction with Current-Clamped Boost

Converter,” published in the conference proceedings of

Power Conversion Electronics ’95/Powersystems World™

’95. A copy of the paper can be obtained by contacting

Toko.

Switching frequency:

Inductance of boost inductor:

f = 100 kHz

L1 = 2.5 mH

Maximum duty ratio of TK75005: DMAX = 0.88

Peak value of ramp current

flowing out of the FB pin:

ISC(PK) = 200 µA

Threshold voltage of the

current-control detector:

VCCD = 0.98 V

Calculations:

For designers who wish to explore other performance

optimizations of the current-clamped boost power factor

corrector, aside from the conference paper Toko offers a

Mathcad© file which can accurately display current

waveforms and predict power factor, harmonic distortion,

and individual harmonic currents. The Mathcad file and the

text which describes how to use it are available from the

Colorado Springs Toko IC Design Center.

The power factor corrector in Figure 7 has been optimized

for general wide-range-input use. In order to obtain the

same performance at power levels other than 100 W, the

control components do not need to change. The power

component values change as follows: C8 scales in

proportion to the power level, and L1 and R8 scales in

inverse proportion to the power level. Typically, although

not directly related to the line-current shaping capability of

the application circuit, C1 and C10 would scale in proportion

to the power level. All the components in the power stage

should have a current rating as needed to accommodate

the power level.

Below is a step-by-step design example, showing how to

determine the resistance of R7 terminating the feedback

pin and the resistance of the current-sense resistor R8, for

the boost corrector of Figure 7.

Assumptions:

Peak value of minimum line voltage:

VI(MIN)(PK) = 2 x VI(MIN) = 120 VPK

Switch duty ratio at peak of minimum line voltage:

D = 1 - VI(MIN)(PK) / VOUT = 0.684

Peak-to-peak ripple current in inductor L1:

I = VI(MIN)(PK) x D / (f x L1) = 0.33 A

Input power at minimum line voltage:

PI = POUT / EFF = 107.5 W

Peak current in L1 (at peak of minimum line voltage):

IL1(PK) = 2 x PI / VI(MIN)(PK) + I/2 = 1.95 A

Output power:

Output voltage:

Minimum line voltage:

Efficiency at 85 Vrms:

POUT = 100 W

VOUT = 380 Vdc

VI(MIN) = 85 Vrms

EFF = 0.93

Resistance of resistor R7 (Note 1):

R7 = DMAX x VCCD / ISC(PK) = 4.312 kohms

January 1999 TOKO, Inc.

Page 7

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