Constant current source in the solar powered led street lights can be divided into the boost, buck, buck three kinds: the so-called step-up its output voltage is higher than the input voltage. Buck output voltage is lower than the input voltage. Buck is to automatically adjust its mode of operation according to the input voltage lower or higher than the output voltage boost or buck.
In the solar powered led street lights, commonly used lead-acid batteries as energy storage device, its voltage is typically 12V or 24V. The required output voltage is connected to the LED structure is determined. In order to make all LED forward current, typically in series with each LED, then the required output voltage is the sum of all series LED forward voltage. For example, suppose that the 10 LEDs in series (Figure 9a), the sum of the forward voltage of about 10×3.3V = 33V. In fact, LEDs produced by various manufacturers vary, but also different between each LED. Therefore, the total of 10 led high bay lights forward voltage is not the same. In fact, the constant current source, the constant current rather than voltage. So, do not need to know the exact value of the sum of the forward voltage, and as long as the higher or lower than the input voltage can be. Here, 12V or 24V battery, it requires a boost type constant current source.
Sense resistor to be as small as possible, in order to avoid the above power consumption. As low as possible for the fact, which means that its internal reference voltage. For chip designers have a certain degree of difficulty. If the reference voltage of 0.1 volts, is a very good chip, this time, the external sense resistor with a very small value, which means the entire system is highly efficient.