The Collocation Design of LED and LED Driver

LEDs have been widely used in illumination and decoration lighting products. When designing LED lights, we need to consider the best kind of LED driver, and the ideal connecting style of loading LED. Only reasonable collocation design can ensure normal operation of the LED.

 1.     LED all in series, figure 1:                                   

Under this circumstance, LED driver must output higher voltage.When LEDs’consistency differs greatly, the voltage

on two ends of LED is different, yet the current through each

LED is same, and the brightness of LEDs is consistent.

When a poor quality LED shorts cut, if using

voltage-stabilizing driver like common RC Buck, the

rest LEDs may be easy to damage. That’s because driver output voltage keeps same, the voltage on two sides of rest LEDs will rise, and the driver output current will also increase. However, if using constant current driver, the normal work of other LEDs will not be influenced because driver output current keeps same.

When a poor quality LED is disconnected, all

LEDs in series will not light. The solution is to parallel a

Zener on both ends of each LED. But the

break-over voltage of Zener must be higher

than LED’s, or the LEDs will not light. Figure2

2.     LED all in parallel, figure3

 It requires LED driver to output larger current, and lower load voltage. On this occasion, the voltage on two ends of all LEDs is equal. If LEDs’ consistency differs greatly, the current through each LED will be different, so does the LEDs’ intensity. The solution is to choose those LEDs with good consistency to apply to products with lower voltage like solar or battery ones .

When a poor LED is disconnected, if using voltage-stabilizing LED driver like voltage-stabilizing switch power supply, the driver output current will decrease, but it may not affect the normal work of other LEDs. If using constant current LED drive, the assigned current of the rest LEDs will increase because driver output current remains unchanged, then it will damage all LEDs.

The solution is to parallel more LEDs as far as                         

possible. When disconnecting a LED, the assigned current

of the rest LEDs may be not too large to affect

normal work of other LEDs. Therefore, power-type LED as LED as shunt load is not suitable for constant current driver

driver.

When a poor quality LED shorts circuit, all LEDs

will not light. But if there are numerous LEDs in series, the current through short-cut LED will be large enough to cause shot-cut LED break-circuit.

 3.     LED in series-parallel connection

For the products which need to use more LED, if all LEDs are in series, LED driver needs to output higher voltage. But if in parallel, LED driver needs to output larger current. So all LEDs in series or parallel, not only does it limit LED usage amount, but also it causes the load current of LED in parallel to be larger and the cost of driver to be increased. The solution is to adopt series-parallel connection.

As figure 4 shows, distributing equally all LEDs in series-parallel, the assigned voltage of each string is same, and so does the current through each LED of the same string. Then the brightness of each LED remains consistent. Meanwhile, it is similar for the current of each string LED.

When a poor quality LED in series shorts circuit, no matter using voltage-stabilizing driver or constant current driver, it means this string LEDs lack 1pc LED and their current will be gotten larger, which will damage this string LEDs easily. The current through the string damaged LEDs is larger, so it will break circuit.

After disconnecting a string LEDs, if using voltage-stabilizing driver, the driver output current will decrease, but it wouldn’t affect normal work of the rest LEDs.

But if using constant current driver, the assigned current of the rest LEDs will increase because the driver output current keeps same, which will damage all LEDs easily. In view of this, the solution is to parallel LED as far as possible. Even disconnecting 1pc LED, the current of rest LEDs is not too large to affect normal work of rest LEDs.

Another way for series-parallel connection, it is to distribute LED averagely and group in parallel, then connect each group in series. See figure 5

When a poor quality LED shorts circuit, no matter using voltage-stabilizing driver or constant current driver, the branch LEDs in parallel will not light. If using constant current LED driver, since the driver output current remains same, the rest LEDs will work normally except the branch short-circuit LED in parallel. Supposing there are many LEDs in parallel and the current of driver is much larger, the current through this short-circuit LEDs will also get larger, which causes that branch LEDs open-circuit easily. Because of numerous LEDs in parallel, after disconnecting the parallel branch of some LED, the assigned current is not large, so all LEDs except that one will still light.

If using voltage-stabilizing driver, when shorts-circuit happens by some poor LED, it means there is lack of one branch parallel LED. In this situation, the voltage of the rest LEDs and the driver output current will both increase. It is possible to damage all LEDs at once. With any luck, just this short-circuit LED is disconnected, yet driver output current will return to normal. Owing to numerous LED in parallel, after disconnecting the branch parallel of one LED, the assigned current of other LEDs is not large, so all LEDs except that one will still light.

Through the above analysis we can see that it is very important to choose collocation of driver and LED in series-parallel. Constant current LED driver is not suitable for parallel system as well as voltage-stabilizing LED driver not fit for series system. All engineers of Deshun Technology will produce the classic LED driver with elaborate and perfect design.