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In general, LED constant current driver ICs are mainly divided into boost type, buck type and buck-boost type (SEPIC). These can also be divided into many different models. The principles for choosing these different types of chips are as follows:

1. The size of the LED power

When selecting a constant current driver chip, first select a chip with sufficient output power to drive the required LED power. That is, the output voltage of the driver chip should satisfy the total LED voltage in series, and its output current should be able to satisfy the total current of the LED being driven.

2. The input voltage level

Although the input voltage is also selective, in general, if the primary power source is solar, its power supply voltage is usually low, so you can use boost type, for example, SLM2841, SLM2846, SLM2842S. If the primary power supply is from AC and DC. When the converter is converted, it can be converted to a relatively high voltage, and then the buck type constant current drive is used, because the buck type usually has high efficiency, for example, SLM2842J, SLM2861 and the like.

3. Input voltage stability

If the input voltage is not very stable and may vary over a relatively large range, such as automotive power, then a buck-boost type, such as the SLM2842SJ, or a high voltage (which covers the range of voltage variations) should be used. Buck chip, such as SLM2842J.

4. LED load situation

The connection of the LEDs can usually be in series or in series and parallel. The greater the number of series connections, the fewer the number of driver chips required. However, there are too many LEDs in series, and there is a certain risk that the entire LED will not light as long as it damages one LED. So usually only string 6 LEDs, no more than 10 at most. Therefore, the output voltage of the driver chip must reach 40V, but a higher output voltage is unnecessary. If you must drive more than 10 series LEDs, you can use the SLM2842 with an external MOSFET. Both the boost, buck, and buck-boost can be externally powered by high-power MOSFETs to increase their output voltage and output current. , thereby increasing its output power. Now Longmao has two booster constant current drive modules with MOS tube, one can drive 12 1W or 3W series LEDs, and the other can drive 15 1W or 3W series LEDs.

5. Constant current control capability for multiple strings of LEDs

If several strings of LEDs are connected in parallel, and the chip has only one output, then its constant current action is only constant current for the total current of these strings, but it cannot guarantee that the current of each string is the same, unless the performance of each string of LEDs It is exactly the same. And if one of the LEDs is broken, at this time, the LEDs of this string will not light, but the current of the constant current will not change, and all the current will be poured into the remaining strings of LEDs. String LEDs double the current of the remaining LEDs, making the remaining LEDs easily burned. Therefore, it is generally recommended to use one driver chip per string of LEDs. That is, do not connect several strings of LEDs in parallel and share a single driver chip control. Unless each LED has parallel canned diode protection, when one LED is damaged, the LED is shorted, and the remaining LEDs of the LED can still be bright, and it will not affect the operation of other string LEDs. In addition, there is a constant current driver chip with multiple constant current capabilities. At this time, a chip can be used to drive several strings of LEDs, such as the SLM2846, which can drive six strings of LEDs and perform independent constant current control for each string of LEDs. , the strings do not interfere with each other.

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