Talking about LED drive circuit

As everyone knows, LED to normal light, it must be able to provide a relatively stable voltage and current, because it is a semiconductor device, so only one-way conduction, so the usual household AC power can not meet the demand, so the LED driving circuit was born, it provides the power to the LED environment we need. How to understand the driver circuit? Here let us learn the relevant knowledge of LED driver circuit:

1 circuit composition

When you need to use a lot of LED products, if all the LED series, the LED driver will need to output a higher voltage: if all the LED in parallel, you need to drive the LED output large current. All the LED in series or in parallel, not only limit the amount of strict LED, and parallel LED load current is larger, the cost of the driver will also increase, the solution is to use mixed mode. The number of LED series and parallel average distribution, so that the distribution of series voltage on the same branch in a LED, with a series of branch current on each LED is basically the same, the same brightness, the current through each series branch are similar.

2 circuit performance analysis

When a series branch has a LED of poor quality and short circuit, whether using regulator drive or constant current drive, will increase the current through the series circuit, it is easy to damage the series branch in LED. Large current through the damage of this string of LED, due to the current through the larger, more performance for the circuit. If a LED series branch is disconnected, if the voltage regulator is used, the output current of the driver will be reduced without affecting the rest of the LED.

If the constant current LED drive mode, due to the driver's output current remains unchanged, the distribution of the current in the remaining LED will increase, easy to damage all the LED. The solution is to parallel LED, so when one LED, not in the rest of the current distribution in LED, without affecting the rest of the normal work of LED.

The advantages of this series parallel circuit is of simple circuit, stable brightness, high reliability, and consistency of the requirements of the device is low, do not need special selection of devices, even if the individual LED single failure on the light emitting component slightly. In the case of large changes in the working environment, the use of this type of light-emitting components is more effective.

There is another method of mixed connection, that is, the average distribution of LED after grouping parallel, and then each group in series. When there is a poor quality and short circuit LED, whether it is the use of voltage regulator drive or constant current drive mode, parallel in this branch of the LED will not be bright. If the constant current LED drive mode is used, the output current of the driver is kept constant, and the other LED can work normally in addition to the shunt branch on the short circuit LED. Assuming that the number of parallel LED is larger, the drive current of the driver is larger, and the current of the LED will be increased by the short circuit. Large current through the short circuit of the LED, it is easy to turn into a circuit. Due to the parallel LED more, disconnect a LED, the average distribution current changes little, the rest of the LED can still work properly, then the entire LED lights only one LED is not bright.

The problem of the first and second series hybrid connection is mainly in a single set of parallel LED, due to the differences in the use of the device and the use of individual LED chips in a single group may lose PN junction characteristics, a short circuit. The individual will make the short circuit failure LED lose the working current of the IF''''''''''''''''lead to the whole group LED out, all from the total current through the short circuit device, and short-circuit current for long time will make the bonding devices within the wire or other part burned, there is open. At this time, the LED does not fail to regain the current, return to normal light, but the operating current IF larger than the original. This is the form of the connection of the light-emitting component appears to be a group of a few LED together with the lights, after a period of time, in addition to one of the LED is not bright, the other LED returned to normal reasons.

3 drive selection

Through the above analysis, drive and load LED serial / parallel way collocation selection is very important, with constant current drive power LED, not suitable for parallel load: similarly, voltage type LED driver is not suitable for selection of series load.