Connection of several LEDs together
1. Series connection
The series connection of LEDs is the usual way to increase the illuminance, for example. In a series circuit, the same current flows through all consumers. It therefore makes sense if all the LEDs connected in series have the same color or, better still, are of the same type with the same characteristic values.
With a sufficiently high supply voltage, several LEDs can be connected in series. A single resistor or a current controller is then sufficient. The number of LEDs must be taken into account when calculating the series resistance, as there is a voltage drop ULED across each LED, which then adds up.
2. Parallel connection
The connection of LEDs in parallel should be avoided as the U/I characteristic curve of an LED is not linear, but approximately exponential. Thus, a small change in voltage leads to a large change in current.
If two or more LEDs (with the same nominal conducting voltage) are connected in parallel, the largest current will flow through the LED with the lowest conducting voltage. As a result, this LED will be brighter and thus also warmer than the other parallel LEDs. The conducting voltage decreases as the temperature increases, as a result of which the effect is amplified and the current increases further until destruction.
Since LEDs made of different semiconducting material, i.e. with different colors, have different conducting voltages, the parallel connection of LEDs with different colors is not permitted. There is variance even in the conducting voltage of LEDs with the same color and from the same manufacturing series. When connecting LEDs in parallel, a series resistor/current controller should be used for each individual LED.
3. LED controller for pixel LEDs
The so-called pixel system is an intelligent method of LED control for several LEDs. “Pixel” LEDs are LEDs with an integrated circuit (IC). With an LED matrix or an LED strip, several LEDs are not connected classically in series; instead, each LED can receive individual signals via a bus communication. In this way, each LED can be controlled individually. These LEDs or LED strips require an LED controller, which serially transmits the communication signals with >100 kHz. Each individual LED is then assigned its own pixel controller.