Application Notes (Continued)
4.6.2 High Compliance Current Sink
A current sink circuit is shown in Figure 21. The circuit
requires only one resistor (RE) and supplies an output cur-
rent which is directly proportional to this resistor value.
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FIGURE 19. Squarewave Generator
4.6 CURRENT SOURCE AND SINK
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FIGURE 21. High Compliance Current Sink
The LMV321/358/324 can be used in feedback loops which
regulate the current in external PNP transistors to provide
current sources or in external NPN transistors to provide
current sinks.
4.7 POWER AMPLIFIER
A power amplifier is illustrated in Figure 22. This circuit can
provide a higher output current because a transistor follower
is added to the output of the op amp.
4.6.1 Fixed Current Source
A multiple fixed current source is show in Figure 20. A
voltage (VREF = 2V) is established across resistor R3 by the
voltage divider (R3 and R ). Negative feedback is used to
4
cause the voltage drop across R 1 to be equal to VREF. This
controls the emitter current of transistor Q1 and if we neglect
the base current of Q1 and Q2, essentially this same current
is available out of the collector of Q1.
Large input resistors can be used to reduce current loss and
a Darlington connection can be used to reduce errors due to
the β of Q1.
The resistor, R2, can be used to scale the collector current of
Q2 either above or below the 1mA reference value.
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FIGURE 22. Power Amplifier
4.8 LED DRIVER
The LMV321/358/324 can be used to drive an LED as shown
in Figure 23.
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FIGURE 20. Fixed Current Source
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FIGURE 23. LED Driver
20
NSC [ National Semiconductor ]
