We are often asked by customers:
Until recently, the main orientation aspect was the voltage. 12V or 24V DC voltage and the current depends on the usage. The power supply unit has to be sufficiently powerful. But now, with the LED as illuminant, we do not anymore connect a load that can be run with constant voltage, e.g. from a battery. Small variations in the voltage result in small changes of the current level.
Constant Current Sources due to LED characteristic curve
LEDs, on the other hand, behave very differently. Their characteristic curve already registers large changes in current for small changes in voltage.
See sketch on the right.
The operation is even unstable if one manages to keep the voltage constant at e.g. 3.3V and maintain a diode current of approx. 350mA. The characteristic curve constantly changes depending on the operating temperature and alternation and scatters from diode to diode. Secure operation is not possible and thermic destruction can occur even with small fluctuations.
Therefore, Constant Current Sources, or LED Drivers, are used. They send a defined and constant current through the LEDs. The voltage measured on the LED is allowed to fluctuate. This ensures reliable operation of the LEDs.
Usual currents for LEDs:
Attention. There are LED illuminants, like GU5.3 (MR16 LED radiator) or LED modules that already have an integrated Constant Current Source. They are run conventionally via constant voltage.
Links for more information: