Rainbow-electronics MAX754 Manual do Utilizador descarregar pdf (Página 11)

MAX753/MAX754

CCFL Backlight and

LCD Contrast Controllers

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Table 3. Spreadsheet Design Equations

T1 Center-Tap Peak Voltage

PARAMETER SYMBOL MIN TYP MAX

TAP,PK

Strike Voltage (V

) V

S,RMS

1100 1500

= -SQRT(2) * I

LAMP,RMS(max)

BAL

* w * SIN(phi)) / n

Discharging Tube Voltage (V

) V

LAMP,RMS

435

Bias Voltage V

LCD

= V

LCD(max)

/ 2 32.6

Output Current I

LCD

0.0245

T1 Turns Ratio (Sec/Pri) n 171

T1 Resonating Inductance L

MAG

0.000045

C9 Value C

RES

2.2E-07

C10 Value C

BAL

1.5E-11

Royer Frequency w = SQRT [1 / (L

MAG

* C

RES

)]

Reference Voltage V

REF

1.25

Second Volts Constant sV 0.000008 2.4E-05

R8 Current-Sensing Resistor R8

= PI() * V

REF

* SQRT(2) /

(2 * I

LAMP,RMS(max)

)

Secondary Voltage Phase vs. Tube

Voltage

phi

= ATAN (-I

LAMP,RMS(max)

BAL

* w * + V

LAMP,RMS

)

Secondary Limit Voltage V

LIM

= V

S,RMS(max)

* 0.9

T1 Center-Tap Limit Peak Voltage = SQRT(2) * V

LIM

/ n

R5/R6 R

OTP,RATIO

= V

REF

/ (D25 - 0.6 - V

REF

)

IN(min)

Full-Load Switching Period T

= sV(min) / V

IN(min)

+ sV(min) /

LCD(max)

- V

IN(min)

)

L2 Inductance L2 = L2(max) * 0.8

= sV(min) ^ 2 / (2 * T

LCD(max)

* I

LCD(min)

)

L2 Peak Currrent = sV(max) / L2(min)

R4/R3 R

LCD,RATIO

= V

REF

/ (V

LCD(max)

- V

REF

)

Input Voltage V

= (2 / PI()) * V

TAP,PK

Discharging Tube Current (I

) I

LAMP,RMS

= 0.28 *

LAMP,RMS(max)

0.005

CCFL Specifications

LCD Contrast Voltage Specifications

Royer Specifications

MAX754 Specifications

CCFL Circuit Calculations

LCD Circuit Calculations

Application Circuit Operating Range

1 2 ... 6 7 8 9 10 11 12 13 14 15 16

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