Motore di ricerca datesheet componenti elettronici |
|
LM1203 Scheda tecnica(PDF) 10 Page - National Semiconductor (TI) |
|
|
LM1203 Scheda tecnica(HTML) 10 Page - National Semiconductor (TI) |
10 / 16 page Circuit Description (Continued) Figure 7 also shows how the contrast control circuit is con- figured Resistors R23 24 diodes D3 4 and transistor Q13 are used to establish a low impedance zero TC half supply voltage reference at the base of Q14 The differential ampli- fier formed by Q15 16 and feedback transistor Q17 along with resistors R27 28 establish a diferential base voltage for Q3 and Q4 in Figure 6 When externally adding or sub- tracting current from the collector of Q16 a new differential voltage is generated that reflects the change in the ratio of currents in Q15 and Q16 To provide voltage control of the Q16 current resistor R29 is added between the Q16 collec- tor and pin 12 A capacitor should be added from pin 12 to ground to prevent noise from the contrast control pot from entering the IC Figure 8 is a simplified schematic of the clamp gate and clamp comparator sections of the LM1203 The clamp gate circuit consists of a PNP input buffer transistor (Q18) a PNP emitter coupled pair referenced on one side to 21V (Q19 20) and an output switch (Q21) When the clamp gate input at pin 14 is high (l15V) the Q21 switch is on and shunts the I1 850 mA current to ground When pin 14 is low (k13V) the Q21 switch is off and the I1 850 mA current source is mirrored or ‘‘turned around’’ by reference diode D5 and Q26 to provide a 850 mA current source for the clamp compara- tor(s) The inputs to the comparator are similar to the clamp gate input except that an NPN emitter coupled pair is used to control the current which will charge or discharge the clamp capacitors at pins 5 8 or 10 PNP transistors are used at the inputs because they offer a number of advan- tages over NPNs PNPs will operate with base voltages at or near ground and will usually have a greater reverse emitter base breakdown voltage (BVebo) Because the differential input voltage to the clamp comparator during the video scan period could be greater than the BVebo of NPN transistors a resistor (R34) with a value one half that of R33 or R35 is connected between the bases of Q23 and Q27 This resis- tor will limit the maximum differential input to Q24 25 to approximately 350 mV The clamp comparator common mode range is from ground to approximately 9V and the maximum differential input voltage is VCC and ground TLH9178 – 8 FIGURE 8 Simplified Schematic of LM1203 Clamp Gate and Clamp Comparator Circuits http www nationalcom 10 |
Codice articolo simile - LM1203 |
|
Descrizione simile - LM1203 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEETIT.COM |
Lei ha avuto il aiuto da alldatasheet? [ DONATE ] |
Di alldatasheet | Richest di pubblicita | contatti | Privacy Policy | scambio Link | Ricerca produttore All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |