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LM1203B データシート(PDF) 9 Page - National Semiconductor (TI) |
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LM1203B データシート(HTML) 9 Page - National Semiconductor (TI) |
9 / 16 page Circuit Description (Continued) collector of Q12 is buffered and level shifted down by Q13 Q14 and Q15 to the base of the output emitter follower Q16 A50X decoupling resistor is included in series with the emit- ter of Q16 and the video output pin so as to prevent oscilla- tions when driving capacitive loads An external resistor should be connected between the video output pin and ground The value of this resistor should not be less than 390X or else package power limitations may be exceeded under worse case conditions (high supply voltage maximum current maximum temperature) The collector current from the video output transistor of each video channel is returned to the power supply at VCC2 pin 23 When making power dissipation calculations note that the data sheet specifies only the VCC1 and VCC2 supply current at 12V supply volt- age with no pull down resistor at the output (ie RL e % see Test Circuit Figure 2 ) The IC power dissipation due to VCC2 is dependent upon the external video output pull down resistor INPUT REFERENCE AND CONTRAST CONTROL SECTION Figure 7 shows the input reference and contrast control cir- cuitry A temperature compensated 28V reference voltage is made available at pin 11 The external DC biasing resis- tors shown should not be larger than 10k because minor differences in input bias currents of the individual video am- plifiers may cause offsets in gain Figure 7 also shows how the contrast control circuit is configured R21 R22 Q22 Q23 and Q24 establish a low impedance zero TC half sup- ply voltage reference at the base of Q25 The differential amplifier formed by Q27 Q28 and feedback transistor Q29 along with R28 and R29 establish a differential base voltage for Q3 and Q4 in Figure 6 When externally adding or sub- tracting current from the collector of Q28 a new differential voltage is generated that reflects the change in the ratio of currents in Q27 and Q28 To allow voltage control of the current through Q28 resistor R27 is added between the collector Q28 and pin 12 A capacitor should be connected from pin 12 to ground to prevent noise from the contrast control potentiometer from entering the IC TLH11489 – 11 FIGURE 7 Simplified Schematic of LM1203B Video Input Reference and Contrast Control Circuits http www nationalcom 9 |
同様の部品番号 - LM1203B |
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同様の説明 - LM1203B |
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