LED drive circuit analysis

　　The choice of driver and load LED series/parallel connection is very important. When driving power LEDs in constant current mode, it is not suitable to use parallel loads: similarly, regulated LED drivers are not suitable to use series loads.

　　1.Circuit composition

　　When more LED products need to be used, if all LEDs are connected in series, the LED driver will need to output a higher voltage; if all LEDs are connected in parallel, the LED driver will need to output a larger current. Connecting all LEDs in series or parallel not only limits the strict usage of LEDs, but also increases the load current of parallel LEDs and increases the cost of the driver. The solution is to use a mixed connection. The number of LEDs connected in series and parallel is evenly distributed. In this way, the voltage distributed on an LED series branch is the same, and the current on each LED in the same series branch is basically the same, with the same brightness. At the same time, the current passing through each series branch Also similar.

　　2. Circuit performance analysis

　　When an LED in a certain series branch is of poor quality and is short-circuited, regardless of whether it is a stabilized voltage drive or a constant current drive, the current passing through the series circuit will increase, and it is easy to damage the LED in the series branch. After a large current passes through the damaged string of LEDs, it often appears as an open circuit due to the large current passing through it. After disconnecting an LED series branch, if a regulated driving method is used, the driver's output current will decrease 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 to the remaining LEDs will increase, easily damaging all the LEDs. The solution is to connect as many LEDs in parallel as possible, so that when one LED is disconnected, the current distributed to the remaining LEDs is not large and will not affect the normal operation of the remaining LEDs.

　　The advantage of this circuit that is connected in series first and then in parallel is that the circuit is simple, the brightness is stable, the reliability is high, and the consistency requirements of the devices are low. There is no need to specially select the devices. Even if individual LED single tubes fail, the impact on the entire light-emitting component will be Also smaller. When the working environment factors change greatly, the effect of using this type of connection form of light-emitting components is ideal.

　　There is another way to connect the mixed connection, which is to divide the LEDs evenly into groups and connect them in parallel, and then connect each group together in series. When an LED is of poor quality and short-circuited, all LEDs connected in parallel in this branch will not light up, regardless of whether it is driven by a stabilized voltage or a constant current drive. If the constant current LED driving method is used, since the output current of the driver remains unchanged, except for the parallel branch connected in parallel to the short-circuited LED, the rest of the LEDs will work normally. Assuming that there are a large number of LEDs connected in parallel and the driving current of the driver is large, the current passing 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 current distribution will not change much, and the other LEDs can still work normally, so only one LED will not light up in the entire LED lamp.

　　The problem with light-emitting components composed of first parallel and then series hybrid connections is mainly in a single group of parallel LEDs. Due to differences in devices and usage conditions, individual LED chips in a single group may lose their PN junction characteristics and cause short circuits. A short circuit of individual devices will cause the non-failed LEDs to lose their working current IF'', causing the entire group of LEDs to go out, and the total current will pass through the short-circuited devices. A longer short-circuit current will cause the bonding wires or other parts inside the device to Burned out, an open circuit appears. At this time, the non-failed LED regains current and resumes normal lighting, but the operating current IF is a little larger than before. This is the reason why when this type of connected light-emitting component appears, several LEDs in a group first go out together. After a period of time, except for one LED that does not light up, the other LEDs return to normal.

　　3. Drive selection

　　From the above analysis, it can be seen that the choice of driver and load LED series/parallel connection is very important. When driving power LEDs in constant current mode, it is not suitable to use parallel loads: similarly, regulated LED drivers are not suitable to use series loads.

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