LED circuit composition and performance

First, circuit composition When more LED products need to be used, if all the LEDs are connected in series, the LED driver will need to output a higher voltage: if all the LEDs are connected in parallel, the LED driver needs a larger output current. Connecting all the LEDs in series or in parallel not only limits the amount of LEDs used strictly, but also increases the load current of the parallel LEDs and drives the cost. The solution is to use hybrid connections. The number of strings and parallel LEDs is evenly distributed. In this way, the voltage distributed on one LED series branch is the same, the current on each LED in the same series branch is also basically the same, the brightness is uniform, and the current through each series branch is also passed simultaneously. Also similar.

Second, the circuit performance analysis When a series branch has a poor quality LED and short circuit, regardless of the use of constant voltage or constant current drive mode, the current through the series circuit will increase, it is easy to damage the series branch LED in the road. After the large current passes through the damaged series of LEDs, due to the large current passing through, a large number of open circuits occur. After disconnecting one LED series branch, if the regulated driving method is adopted, the output current of the driver will be reduced without affecting the normal operation of all remaining LEDs.

If a constant current LED driving method is used, since the output current of the driver remains unchanged, the current distributed in the remaining LEDs will increase, and it is easy to damage all the LEDs. The solution is to connect the LEDs in parallel as much as possible so that when one LED is disconnected, the current distributed in the rest of the LEDs is not so large that the remaining LEDs will not work properly.

The advantage of this series-connected and parallel-connected circuit is that the circuit is simple, the brightness is stable, the reliability is high, and the consistency of the device is lower. There is no need to specially select the device, even if the individual LED single-tube failure, the impact on the entire light-emitting assembly Also smaller. In the case of a significant change in the working environment, the use of this type of connection of light-emitting elements is ideal.

There is another connection method in the hybrid connection mode. That is, the LEDs are evenly distributed and grouped in parallel, and each group is connected in series. When an LED has a poor quality and is short-circuited, whether in a regulated or constant-current driving mode, the LEDs connected in parallel in this branch will all be off. If a constant current LED driving method is adopted, since the output current of the driver remains unchanged, all the other LEDs operate normally except for the parallel branch connected in parallel to the short-circuit LED. Assuming that the number of LEDs connected in parallel is large, the drive current of the driver is large, and the current through this short-circuited LED will increase. After a large current passes through this short-circuited LED, it can easily become an open circuit. Since there are many LEDs connected in parallel, after one LED is disconnected, the average distribution current does not change much, and the rest of the LEDs can still work normally. Then only one LED in the entire LED light is off.

The problem of the light elements formed by connecting the first and second strings in series is mainly in a single set of parallel LEDs. Due to the difference in devices and conditions of use, individual LED chips in a single group may lose the PN junction characteristics and cause a short circuit. The short circuit of individual devices will cause the non-failed LED to lose the operating current IF'''', which will cause the entire group of LEDs to go out and the total current to pass through the short-circuit device. A short-term short-circuit current will make the bonding wire inside the device or Other parts burned and an open circuit appeared. At this time, the non-failed LED regains current and resumes normal light emission, except that the operating current IF is larger than the original one. This is the reason that this type of connection of light-emitting elements occurs first when several LEDs in a group are extinguished together, and after a period of time, in addition to the failure of one of the LEDs, the other LEDs return to normal.

Third, the driver's choice Through the above analysis shows that the driver and the load LED string / parallel mode is very important, when the constant-current drive power LED, it is not suitable for parallel load: Similarly, the voltage regulator LED driver is not Suitable for series loads.