Ayrton Senna
With the recent deaths of Niki Lauda and Robert J Hawke, we are feeling a little like the old world is slipping away one soul at a time. Despite that perception, however, Ayrton Senna's warning about race circuits still feels very current (small joke) as we explore the wonders of the LM317 chip and associated circuits.
At around AU9c each delivered, they perform the improbable double act of being able to control voltage in one configuration and current in another. We did have a few accidents in these circuits along the way, and thus we bid farewell to a few LEDs and a trimpot that let out the magic smoke in the pursuit of understanding.
Constant Current
Assuming the supply is up to the task, the LM317 can keep current constant as the load changes (in this case more LEDs added to the mix). The current can be selected and maintained using a variable resistor in the following configuration.
In another guise, this versatile unit can also be used to select a voltage output, again being careful to get the connections right to avoid the stinky fails.
We're not convinced that these are particularly efficient circuits, but given that the LM317 datasheet boasts stats of 1.25-37 V output from 3-40V input, and current peaks of 1.5A, we'll forgive any problems in exchange for cheap and versatile. It's been around since 1976, and likely to stay in our kit for a few more years yet.
Nice one.
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