AN921| Application Note
Maxim > App Notes > AMPLIFIER AND COMPARATOR CIRCUITS Keywords: current source, current sense amplifier, amp, compliance, adjustable current source, constant current source, battery charger
Dec 01, 1995
APPLICATION NOTE 921
Variable, Linear Current Source Operates On 5V
Abstract: The circuit described uses a current-sense amplifier and low-dropout linear regulator to make an adjustable current source with a compliance of zero to 5V. The control voltage can come from a separate voltage input or can be generated under digital control using a 10 or 12 bit, serial or parallel, D to A converter. The current regulator of Figure 1 features a low-dropout voltage regulator (IC2) whose voltage feedback is derived from the input current by a current-sense amplifier (IC1). This connection allows the regulator IC to oppose any change in output current. When powered from 5V, the current source has a compliance range of 0V to 4.7V.
Figure 1. IC1 converts R1 current to a proportional output voltage, enabling the voltage regulator (IC2) to produce a regulated output current. To set a specific, regulated IOUT level between 0mA and 250mA, apply 0V to 5V at ICONTROL: 0V sets IOUT = 250mA, and 5V sets IOUT = 0mA. Alternatively, a D/A converter can provide digital control of IOUT. For 12-bit
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