Chip package is also very important, the QFN chip package is clearly better than the chip in a TSSOP package, thermal resistance is much lower. In the purchase of the module should understand the used chip package (as far as possible in a QFN package, to avoid using the TSSOP package).
Now give a concrete example to illustrate: if the solar low voltage led landscape lights uses a 12V battery, the load is 8-string 3 and 1W LED load voltage at the output is roughly 26.4V, the current is 1.05A, the output power of 27.7 W. If the 12V battery, the highest time in the voltage is 14.8V, the step-up ratio is 1.78, then do not have the radiator when the QFN package case temperature is about 60 degrees. Acceptable, but when the battery voltage drops to 10.8V, the step-up ratio becomes 2.44 times, and this time the shell temperature will rise to more than 70 degrees, if the TSSOP package case temperature will rise to about 85 degrees is not allowed!
In addition to the need to consider the case temperature, but also consider the maximum input current. SLM2842 the maximum input current of 3A. In the calculation of the maximum input current, we must consider the efficiency of the constant current module itself. Assumed to be 90% at the same time assumes that the output power is 32W, divided by 0.9 is 35.5W.
The number of series low voltage led landscape lights should be less than 10, this is because LED lamps have a safety requirements. Voltage led high bay lamps shall not exceed the maximum safety extra low voltage (SELV) according to EU standards of the IEC 61347-2-13 (5/2006), the requirements for DC or AC powered LED module, which is the work output voltage ≤ 25 Vrms (35.3 Vdc), so the total number of series LEDs is not more than 10