LED driver.

Driver is a thing which gives constant current regardless of what you will connect to it.

LED's work on current. They consume needed voltage without noticing it. If we connect LED to 12 volt DC, he consume needed (for example) 2 volts and spare voltage will go further. (if there is nothing else all 12 volts will be on LED and it will most likely burn).

LED is just like a diod, it's resistance changes according to the voltage, it has low resistancein one direction, and high (Mohms) resistance in the other.

LED driver supports constant current for LED's, average resistor is also a driver (but very bad). Usually it is enough for simple applications, but if we want to make LED lighting, or connect LED to the power line, it's better to use special IC's or PCB's.

Drivers have 2 main characteristics: output current and power. e.g. 10 W, 200 mA, so maximum voltage on output will be 10 / 0.2 = 20 V. So if we have 2 V 200 mA LED's we can connect 10 of them (or less) in series to our driver.

Why they are better than power supplies ? Driver will do everything it can to keep constant current on the output, changes in temperature, voltage or anything else. There are good power supplies, but they are multifunctional, so they are more expensive and bigger than drivers which are designed to perform only 1 task.

Also it's better to buy driver and after that search for suitable LED's, because there is a variety of LED's with different characteristics, but not so much drivers.

Basic drivers:

Resistor

Capacitor circuit

LM317 

HV9910

Thanks to:

led22.ru