current sink

2 Articles

Precision Current Sources By The Numbers

November 14, 2025 by 1 Comment

It isn’t unusual to expect a precisely regulated voltage in an electronic project, but what about times when you need a precise current? Over on EDN, prolific [Stephen Woodward] explains how to use a precision Zener diode to get good results. [Stephen] takes you through the math for two topologies and another circuit that uses a pair of bipolar transistors.

You might wonder why you need a precise current source or sink. While it is nice to drive things like LEDs with a constant current, you probably don’t need ultra-precise currents. However, charging a capacitor with a constant current produces a very nice linear voltage ramp. When you use a resistor to bias collector current in a bipolar amplifier, you are just poorly imitating a constant current source, too. That’s just two of many examples.

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Circuit VR: Sink Or Swim With Current Sources

May 3, 2018 by 22 Comments

If you got your start in electronics sometime after 1980 your first project might well have been to light up an LED. Microcontroller projects often light up an LED, too, and a blinking LED is something of the “hello world” program for embedded systems. If you tried lighting up your LED with a 9 V battery directly — not that you’d admit to it — you found it would light up. Once, anyway. The excess current blows up the LED which is why you need a current-limiting resistor. However, those current limiting resistors are really a poor excuse for a current source or sink. In many applications, you need a real current source and luckily, they aren’t hard to create.

As always with Circuit VR, we’ll be using LT Spice to examine the circuits. If you need a quick tutorial, start here and come back after that. If you use Linux, don’t be dismayed. I run LT Spice under WINE and it works great. You can find all the Spice files on GitHub.

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