LED drivers are basically regular power supply, which are designed to match the characteristics of an array of LEDs or a single LED in your application. The primary function of a LED driver is the maintenance of forward current as well as forward voltage needed to operate the LEDs over different conditions. LEDs are basically current devices and thus the maintenance of consistent current is a prime requirement. You may also find an additional circuitry in an LED driver for the purpose of dimming and also for separate control of one LED or more. It is worth knowing that white LEDs operate at a much higher forward voltages than the standard yellow, red and green LEDs. However, the way to design drivers for both the types is the same.
Calculate the total current and forward voltage requirements for LED drivers. Thereafter, determine the total number of LEDs in your application and the way they are configured. If you are making a single LED, it would just be the forward voltage and forward current for that particular LED. If you have multiple diodes in series then the total forward voltage would be the sum of all the forward voltage taken together of the entire the diodes in the series string. The total forward voltage for multiple LEDs in a parallel circuit is the sum of the entire forward voltages in a single branch. The total forward current would be the sum of the entire forward currents through each and every one of the branches.
It is also important to determine the driver circuit. This does not depend only on the LED requirements but also on the power sources you are planning to use. It may happen that you are using a constant current source or voltage and the entire power requirement is comparatively low. In order to handle such situation, just use a current limiting resistor for current limiting. However, if you are using LEDs in particularly an application, which is battery operated, then the resistance method is not supposed to be optimal. This is simply because the brightness would decrease since the battery voltage would decrease as time passes. The solution to this problem is to use a linear regulator. The function of the regulator would be to maintain constant current down to it’s own dropout voltage. However, if you are using high-power applications, it is better to use a step down or step up switching regulator. It should be taken into account that switching regulators are way more efficient than linear regulators. This is more applicable when the concerned applications require high current loads.
It is always advisable to visit different websites of parts manufacturers and distributors of LED drivers. You would find a huge range of switching and linear LED driver ICs available from the house of innumerable manufacturers. You would also find data sheets as well as application notes containing information about the different characteristics of specific LED driver ICs along with guidelines and recommendations for using the items in your applications.