Since LED chips have low power and low operating voltage, a large number of series and parallel connections must be used in the production of lamps to meet the power requirements. How to connect these chips is an issue we must take seriously. Otherwise, the service life of the lamp will be greatly shortened, resulting in the embarrassing situation of “saving energy but not saving money”.
As an electronic component, LED has a very special side, which is nonlinearity. Simply put, as long as the voltage applied to the LED changes a little, it will cause a large change in the chip current. If not handled properly, it will seriously affect the life of the LED. Here are the advantages and disadvantages of various connection methods of LED chips:
1. Series connection
Series connection is the most reasonable connection method for LED chips
The basic feature of the series circuit is that the current on all LED chips is equal, so the power difference between each chip is equal to their voltage difference, and will not be higher than it. Therefore, the series connection method has the strongest tolerance for the inconsistency of LED chips.
The only disadvantage of the series circuit is that once the chip is open, the entire lamp or the entire string of lights will not light up, and the short circuit has basically no effect. However, the proportion of open circuits in chip failures is lower than that of short circuits. Therefore, the overall failure rate of series circuits is very low.
If you want to be foolproof, you can connect a 4v~5v voltage regulator in parallel to each chip to provide a path when the chip is open, but the cost will be slightly higher. However, it is worth it for some special occasions with high requirements.
2. Parallel connection
Parallel connection is one of the most uncertain connection methods for LED chips, which will amplify the consequences of LED inconsistency and cause premature damage to the lamps. If you are not sure whether you can purchase chips with highly consistent vF values, do not use parallel connection.
Now take 3.0ⅴ and 3.6ⅴ chips as an example. Their average vF value after parallel connection will be higher than 3.0, resulting in excessive current of 3.0ⅴ LED. As the temperature rises, vF will further decrease and power consumption will continue to increase. Such a vicious cycle will greatly shorten the life of low vF value chips in the parallel group.
If this chip has a short circuit fault, the entire group of chips will not light up. If the power supply output current is large, it will quickly burn this chip into a short circuit, and then distribute the current that should belong to it to others, thereby accelerating the aging speed of this group of chips.
3. Parallel first, then series connection
Parallel first, then series connection reflects the advantages of series connection, but it cannot avoid the disadvantages of parallel connection, so it is not the best connection method. However, this mode is most commonly used in fluorescent lamps. For example, 18w fluorescent lamps are basically 4 parallel and 24 series.
This connection method is based on the premise that once a chip is open, other chips can continue to light up. On the surface, it has little impact, but it will accelerate the damage rate of the remaining chips. Of course, if chips are purchased in large quantities, it is possible to classify the chips more finely and better ensure the consistency of the chips, which is also the basis for adopting this connection method.
4. Series connection first, then parallel connection
Serial connection first, then parallel connection absorbs the advantages of both methods and is a more reasonable LED connection method.
Especially for some small businesses in the form of home workshops, it is difficult to ensure the consistency of chips, so try to adopt this mode to maximize the service life of the lamps. Blindly imitating the so-called parallel connection first, then series connection mode of large factories will not work.
The above briefly introduces the advantages and disadvantages of various LED chip series and parallel connection modes. In my personal experience, when designing aluminum base plates for lamps, series connection should be given priority, followed by series connection first and then parallel connection, and parallel connection first and then series connection should be avoided as much as possible. As for the low-voltage mode of all parallel connections, if conditions permit, it is best to use a DC-DC boost module to change to series connection.