LED used as a Constant Current Source

An LED bandgap is used here, as a reference, for a constant current source. Most LEDs can be used, but with different colours - come varying forward voltages. Whatever you do, don't exceed the parameters of the transistor if much more power is required - use a power transistor. This circuit can be operated by; using a 9VDC PP3-type battery - check for correct polarity, and with a band gap of only 2VDC (or less), designs can get close to the +ve rail. Applications include Amplifiers, Wave Shaping and Analogue Electronics, to name but a few. However, I do not consider this a Precision Current Source.

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Notes: Approximate maths: R1 = (Desired Compliance Supply Voltage - LED Forward Voltage) / 0.002 Amps. R2 = 1.13VDC / Desired Output Current. I used a Red LED with a forward Voltage of 1.78VDC at 0.0018 Amps, however, other LEDs will have different values.

Links: BC559C datasheet: https://datasheetspdf.com/pdf/1140467/CDIL/BC559C/1 ... https://www.youtube.com/watch?v=oexFlxcylhU