If you examine the schematic diagram provided by the manufacturer, if one is provided, they normally show a symbol for a current source. They give no details, nor do they generally show any sensitivity to input supply. You (Erik) stated that the component to which you referred, provides a controlled current irrespective of the voltage, i.e. even if the external supply voltage varies in real time between 28 volts and 3 volts, it will produce a constant output current that won't cause any variation in brightness of the driven LED (the device, is, after all, an LED driver. I suspect this means it uses an internal voltage regulator of some sort.

Just for the sake of discussion, I'd refer you to
http://en.wikipedia.org/wiki/Curr...e_with_LED
Figure 6. That's an active circuit that produces a constant current, but the current, as you'll see, is dependent on a zener, which provides are pretty constant voltage source.

If you look at Figure 7, you'll see that LM317 to which I referred. From a closely regulated voltage supply, as what the LM317 can provide, if implemented correctly and properly decoupled, Chico could construct any sort of current source he likes. He could even construct a pure current-source, as shown in Figure 7, though that really relies on the closely regulated 1.25-volt regulation of the LM317. That one seems to care very little what the external positive supply voltage is, within limits, but it does, ultimately, depend on the closely controlled voltage of the LM317 output.

I'm not sure what Erik had in mind with respect to the ST2221A,
http://www.elektronik.ropla.eu/pdf/stock...t2221a.pdf
nor can I guess what purpose the built-in shift register would serve. Now, this may not be the part that he meant, but it's pretty clear that the one I found requires a regulated Vcc, as its output current is controlled by a resistor.

RE