For high power LEDs, it is very inefficient to use resistors to limit current. The resistor can end up dissipating more energy as heat than the LED does. So for a lot of the power LEDs out there, there are power supplies which are AC-to-DC power supplies whcih also limit current. My question is how does one go about designing a DC-to-DC (no voltage change) current source like this rather than buying off the shelf? For example, a white power LED might have a forward current of 30V and take up to 1.5A. Let's say you already have a power supply that can provide 30V and 5A. How do you design a circuit so that it limits current to 1.5A? At that point I would assume you could control brightness with a logic level MOSFET and the PWM capability of the Arduino. Does anyone have a good reference concerning designing such a current limiting circuit? Thank you.
If you already have a 30V supply you are in trouble since a linear current source will need
voltage headroom to operate.
The typical efficient solution is a DC-DC converter operating from a standard voltage
like 12V and producing a constant current output - ie a chip designed for this specific
purpose. Such current sources will have a maximum and minimum output voltage
given in the datasheet.
If you genuinely have a 30V constant voltage supply you will need a boost (or buck-boost)
DC-DC converter with constant voltage output. For such a small voltage ratio efficiency
can be very good.
In theory if you have a 30V supply with a voltage-trim input then that could be used to
give current-control feedback.