OBSOLETE

LM2407

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SNOS021C – AUGUST 1999 – REVISED APRIL 2013

THEORY OF OPERATION

The LM2407 is a high voltage monolithic three channel CRT driver suitable for high resolution display

applications. The LM2407 operates using 80V and 12V power supplies. The part is housed in the industry

standard 11-lead TO-220 molded plastic power package.

The circuit diagram of the LM2407 is shown in Figure 1. A PNP emitter follower, Q5, provides input buffering. Q1

and Q2 form a fixed gain cascode amplifier with resistors R1 and R2 setting the gain at -14. Emitter followers Q3

and Q4 isolate the high output impedance of the cascode stage from the capacitance of the CRT cathode which

decreases the sensitivity of the device to load capacitance. Q6 provides biasing to the output emitter follower

stage to reduce crossover distortion at low signal levels.

Figure 3 shows a typical test circuit for evaluation of the LM2407. This circuit is designed to allow testing of the

LM2407 in a 50

Ω environment without the use of an expensive FET probe. In this test circuit, two low inductance

resistors in series totaling 4.95 k

Ω form a 100:1 wideband, low capacitance probe when connected to a 50Ω

coaxial cable and a 50

Ω load (such as a 50Ω oscilloscope input). The input signal from the generator is ac

coupled to the base of Q1.

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