Widlar current source — Free Electronics Illustration

Electronics

Widlar current source

Compact black schematic of a Widlar current source using two matched bipolar junction transistors arranged side by side as a current-mirror pair. One transistor is diode-connected with its base tied to its collector to form the reference branch, and the bases of both transistors are connected together. The second transistor is the output branch and has a clearly visible zigzag resistor in series with its emitter lead, creating emitter degeneration and reduced output current. Collectors are at the top, emitters downward, with separate reference-current and output-current terminals or branches shown clearly; current-direction arrows may be included. Use standard clean black line-art transistor symbols, emphasizing the asymmetry created by the emitter resistor on the output transistor.

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