From Current Sources & Voltage References

While much of this book focuses on how to build current sources using different kinds of discretes, this chapter looks at some dedicated, monolithic IC current source circuits. These devices can be used in many diverse applications requiring microamps to several milliamps and are readily available in either throughhole or surface-mount packages. Actually, two dedicated monolithic current source ICs exist in the U.S. analog marketplace. One of them is National Semiconductor's LM134 series, and the other is TI/Burr-Brown's newer REF-200 (which we will review later in this chapter).

10.1 National's LM134 a Monolithic IC Current Source

Of all the thousands of analog semiconductor products that have been introduced and then later discontinued over the past two decades, one that has survived the test of time and changing market needs is National Semiconductor's venerable LM134. This is a dedicated three-terminal adjustable bipolar/JFET current source IC. The LM134 was originally designed by Carl Nelson at National Semiconductor and introduced in the late 1970s. (Carl Nelson is now with Linear Technology.) Over the past 25 years, it has been at the cornerstone of thousands of electronic designs around the world, and because of its popularity, it is likely to be in National's product lineup for a long time to come.

The LM134 family has various options (134/234/334), which are shown in Table 10.1, and the range is second-sourced by Linear Technology Inc. From the outset the LM134 was designed for ease of use and to play a dual role: to be both an accurate...

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IC Timers
IC timers are semiconductor circuits that generate or set timing for electronic circuits.
IC Linear Voltage Regulators
Integrated circuit (IC) linear voltage regulators use voltage-controlled sources to force a fixed voltage to appear at their output terminal.
Operational Amplifiers
Operational amplifiers (op amps, op-amps) are general-purpose, closed-loop devices that are used to implement linear functions.
IC Analog Switches
IC analog switches are integrated circuits (ICs) that allow electric current to flow when closed and prevent current from flowing when open. They are often used to interface analog signals to digital controllers.
RS-232, RS-422, and RS-485 Interfaces
RS-232, RS-422, and RS-485 are standard interfaces approved by the Electronic Industries Association (EIA) for connecting serial devices. They are serial communication standards providing asynchronous communication capability with hardware flow control, software flow control, and parity check.

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