ML4819CS datasheet(11/15 Pages) MICRO-LINEAR

11 / 15 page

ML4819

The value of R9 (pin 3) depends on the selection of R2

(pin 6).

ImA

IN MAX PEAK

SINE PEAK

260 1 414

072

510

()

Ω

(12)

CLAMP

IN MIN PEAK

4 8 510

80 1 414

()

Ω

(13)

Choose R9 = 27k

The peak of the inductor current can be found

approximately by:

LPEAK

OUT

IN MIN RMS

1 414

1 414 200

314

()

(14)

Next select NC, which depends on the maximum switch

current. Assume 4A for this example. NC is 80 turns.

CLAMP

LPEAK

49 80

100

=Ω

(15)

Where R11 is the sense resistor, and VCLAMP is the current

clamp at the inverting input of the PWM comparator. This

clamp is internally set to 5V. In actual application it is a

good idea to assume a value less than 5V to avoid

unwanted current limiting action due to component

tolerances. In this application VCLAMP was chosen as 4.8V.

Having calculated R11 the value SPWM and of R18 can

now be calculated:

PWM =

−

×=

380

100

0 225

knF

PWM

2 5 28 8

0 7

0 225 10

××

≅

.( .

)

Ω

(16)

Choose R18 = 33k

The following values were used in the calculation:

R9 = 27kW

ASC = 0.7

RT = 14kW

CT = 1nF

VOLTAGE REGULATION COMPONENTS

The values of the voltage regulation loop components are

calculated based on the operating output voltage. Note

that voltage safety regulations require the use of sense

resistors that have adequate voltage rating. As a rule of

thumb if 1/4W through-hole resistors are used, two of

them should be put in series. The input bias current of the

error amplifier is approximately 0.5µA, therefore the

current available from the voltage sense resistors should

be significantly higher than this value. Since two 1/4W

resistors have to be used the total power rating is 1/2W.

The operating power is set to be 0.4W then with 380V

output voltage the value can be calculated as follows:

380

0 4

360

() / .

Ω

(17)

Choose two 178k

W, 1% connected in series.

Then R6 can be calculated using the formula below:

REF

356

380

4 747

−

Ω

(18)

Choose 4.75k

W, 1%. One more critical component in the

voltage regulation loop is the feedback capacitor for the

error amplifier. The voltage loop bandwidth should be set

such that it rejects the 120Hz ripple which is present at

the output. If this ripple is not adequately attenuated it

will cause distortion on the input current waveform.

Typical bandwidths range anywhere from a few Hertz to

15Hz. The main compromise is between transient

response and distortion. The feedback capacitor can be

calculated using the following formula:

RBW

kHz

3 142

3 142 356

044

××

=µ

Ω

(19)

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