LM122 National Semiconductor, LM122 Datasheet - Page 8

• Manufacturer Part Number: LM122
• Description: Precision Timers
• Manufacturer: National Semiconductor

Figure 6 indicates the ability of the timer to interface to digi-
Typical Applications
30V Supply Interfacing with 5V Logic
tal logic when operating off a high supply voltage V
swings between
5 for medium speed TTL If the logic is sensitive to rise fall
time of the trailing edge of the output pulse the trigger pin
should be low at that time
Astable Operation
The LM122 can be made into a self-starting oscillator by
feeding the output back to the trigger input through a capac-
itor as shown in Figure 7 Operating frequency is 1 (R
R
is approximately 2R
should be as small as possible The minimum value is deter-
FIGURE 4 Time Out on Power Up (Relay Energized Until
1
)(C
FIGURE 6 30V Supply Interfacing with 5V Logic
FIGURE 5 5V Logic Supply Driving 28V Relay
t
) The output is a narrow negative pulse whose width
R
t
C
t
Seconds After V
a
5V and ground with a minimum fanout of
2
C
f
For optimum frequency stability C
CC
(Continued)
is Applied)
TL H 7768–14
TL H 7768–15
TL H 7768–16
OUT
t
a
f
8
Figure 8 shows the LM122 connected as a one hour timer
mined by the time required to discharge C
nal discharge transistor A conservative value for C
chosen from the graph included with Figure 20 For frequen-
cies below 1 kHz the frequency error introduced by C
few tenths of one percent or less for R
One Hour Timer with Reset and Manual Cycle End
with manual controls for start reset and cycle end S1
starts timing but has no effect after timing has started S2 is
a center off switch which can either end the cycle prema-
turely with the appropriate change in output state and dis-
charging of C
change in output In the latter case a new timing period
starts as soon as S2 is released
FIGURE 8 One Hour Timer with Reset
t
or cause C
and Manual Cycle End
FIGURE 7 Oscillator
t
to be reset to 0V without a
t t
t
through the inter-
500k
See Chart
TL H 7768 – 17
TL H 7768 – 18
TL H 7768 – 19
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Electronics
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