Since the I–V curve of a LED lamp is sensitive in voltage,
as shown in Fig. 1. A slight variation of applied voltage
may cause abrupt change of current which may
damage the LED. The constant-voltage driver was thus
not recommended for LED. Instead, the constant-current
driving is widely used in commercial products. A DC/DC
converter with constant-current output for LED is thus
needed in solar LED lighting system. This creates the problems
of energy loss in the control circuit of the converter,
decreasing solar system reliability, and increasing cost.
A lot of commercial DC/DC constant-current driver
products for LED illumination are available. However,
the energy conversion loss for high-power LED is high
(>14%) at partial load condition, for example, the product
of Zetex Semiconductors Plc. (2008). This happens when a
dimming control of LED is employed. The cost of a DC/
DC constant-current driver for 30–200 W LED is around
30–50 USD. Moreover, the lifetime of high-power DC/
DC converter is expected to be around 3 years due to the
capacitor failure in the circuit.