LM2479 datasheet(3/4 Pages) NSC

3 / 4 page

Typical Performance Characteristics

CC = +120V), Test Circuit - Figure 3 unless otherwise specified.

THEORY OF OPERATION

The circuit diagram of the LM2479 is shown in Figure 1. The

DC clamp circuit amplifies the input signal by -18 and the

gain is set by the resistor ratio of 18R and R. The output

requires pull-up resistor to 120V. Figure 2 shows the test

circuit used for evaluation of the LM2479 Clamp Amplifier. A

high impedance voltmeter (100M

Ω) is used for DC measure-

ments at the output. The DC transfer function is shown in

Figure 4.

APPLICATION HINTS

Power Supply Bypass

The LM2479 should have proper power supply bypassing for

optimum performance. A 0.1µF capacitor should be con-

nected from the supply pin, V

cc, to ground, as close to the

supply and ground pins as is practical. Additionally, a 1.0µF

electrolycelectrolytictic capacitor should be connected from

the supply pin to ground. The electrolytic capacitor should

also be placed reasonably close to the LM2479’s supply and

ground pins.

Application Circuit

The application circuit shown in Figure 5 is designed to help

clamp the voltage at the output of the driver to the desired

level. Capacitor C

4 stabilizes the entire node at the anode of

the clamp diode, D

3, by creating a low impedance at high

frequencies. Figure 5 also shows the standard application

circuit topology when used with an LM246X CRT driver. It

shows all the components necessary to optimize perfor-

mance as well as to protect against damage from a CRT arc

event. No additional components are required to protect the

LM2479 from arc damage.

Demonstration Hardware

National Semiconductor has designed a demonstration

neckboard for the LM126X, LM246X, and the LM2479

chipset. To obtain demonstration boards contact the National

Semiconductor Sales Office in your region.

DS101391-4

FIGURE 4. V

out vs Vin

DS101391-7

FIGURE 5. One Channel of the LM2479 and LM246X

Application Circuit

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