LM1207N National Semiconductor, LM1207N Datasheet - Page 16

• Manufacturer Part Number: LM1207N
• Manufacturer: National Semiconductor

Specifications of LM1207N

• Lead Free Status / RoHS Status: Not Compliant

http
Figure 12 is a simplified schematic of the Clamp Gate cir-
Circuit Description
CLAMP GATE CIRCUIT
cuit A voltage reference is setup by Z3 and by Q104 and
Q105 connected as diodes generating a 7V base drive to
Q94 Q99 and Q101 Q94 is used to bias the input stage
This stage is designed to accept TTL levels at pin 14 Q95
and Q97 form a differential pair The base of Q97 is set to
2 1V by Q99 driving the voltage divider formed by R77 and
R78 In a balanced condition the base of Q95 is also at
2 1V Q96 is connected as a diode and the current flow thru
it is mirrored into Q98 Also the input to pin 14 would be one
diode drop below 2 1V or around 1 4V R74 is added to the
www national com
FIGURE 11 Simplified Schematic of LM1205 LM1207 Clamp Comparator Circuit
(Continued)
16
input for current limiting during any possible voltage surge at
pin 14 With no resistors at the emitters of Q96 and Q98 this
circuit will quickly switch Below 1 4V (1 2V typical) Q95 is
turned on and Q97 is turned off Above 1 4V (1 6V typical)
Q97 is turned on and Q95 is turned off With Q97 turned on
Q100 is also turned on This pulls the current thru R79 to
ground turning off Q102 and Q103 Remember Q102 is a
current mirror to Q86 in the clamp comparator With Q102
turned off the clamp comparator is also turned off When
the input signal goes below 1 2V Q97 and Q100 will be
turned off This allows Q102 to turn on turning on the clamp
TL H 11881 – 19