The LM is a high voltage monolithic three channel CRT driver suitable for high resolution display applications. The LM operates with 80V and 12V power supplies. The part is housed in the industry standard 9-lead TO molded plastic power package. The circuit diagram of the LM is shown in Figure 1. The PNP emitter follower, Q5, provides input buffering.
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The LM is a high voltage monolithic three channel CRT driver suitable for high resolution display applications. The LM operates with 80V and 12V power supplies. The part is housed in the industry standard 9-lead TO molded plastic power package.
The circuit diagram of the LM is shown in Figure 1. The PNP emitter follower, Q5, provides input buffering.
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 cross- over distortion at low signal levels.
Figure 2 shows a typical test circuit for evaluation of the LM In this test circuit, the two 4. The input signal from the generator is ac coupled to the base of Q5. Application Hints National Semiconductor NSC is committed to provide ap- plication information that assists our customers in obtaining the best performance possible from our products.
The fol- lowing information is provided in order to support this com- mitment. The reader should be aware that the optimization of performance was done using a specific printed circuit board designed at NSC. Variations in performance can be realized due to physical changes in the printed circuit board and the application. Therefore, the designer should know that com- ponent value changes may be required in order to optimize performance in a given application.
The values shown in this document can be used as a starting point for evaluation purposes. When working with high bandwidth circuits, good layout practices are also critical to achieving maximum per- formance. The application circuits shown in this document to optimize performance and to protect against damage from CRT ar- cover are designed specifically for the LM If another member of the LMX family is used, please refer to its datasheet. Since the LM is a wide bandwidth amplifier, proper power supply bypassing is critical for optimum performance.
Improper power supply bypassing can result in large over- shoot, ringing or oscillation. Spark gaps, in the range of V, connected from the CRT cathodes to CRT ground will limit the maximum voltage, but to a value that is much higher than allowable on the LM This fast, high voltage, high energy pulse can damage the LM output stage. The application circuit shown in Figure 9 is designed to help clamp the voltage at the output of the LM to a safe level.
The clamp diodes, D1 and D2, should have a fast transient response, high peak current rating, low series impedance and low shunt capaci- tance. FDH or equivalent diodes are recommended. Do not use 1N diodes for the clamp diodes. D1 and D2 should have short, low impedance connections to V CC and ground respectively. The cathode of D1 should be located very close to a separately decoupled bypass capacitor C3 in Figure 9.
The ground connection of D2 and the decoupling capacitor should be very close to the LM ground. This will significantly reduce the high frequency voltage transients that the LM would be subjected to during an arcover condition. Resistor R2 limits the arcover current that is seen by the diodes while R1 limits the current into the LM as well as the voltage stress at the outputs of the device.
Having large value resis- tors for R1 and R2 would be desirable, but this has the effect of increasing rise and fall times. Inductor L1 is critical to reduce the initial high frequency voltage levels that the LM would be subjected to. The inductor will not only help protect the device but it will also help minimize rise and fall times as well as minimize EMI. For proper arc protection, it is important to not omit any of the arc protection compo- nents shown in.
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Features, Applications The is an integrated high voltage CRT driver circuit designed for use in color monitor applications. The IC is packaged in an industry standard 9-lead TO molded plastic power package. See Thermal Considerations section. Note 2: Operating ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed.