The power supply system for LED streetlights differs from that of traditional light sources; a constant-current driver-specifically required by LEDs-is fundamental to their proper operation, whereas simple switching power supply designs often lead to damage to the LED components. The ability to safely operate a tightly packed array of LEDs is a key criterion for evaluating LED streetlights. LED driver circuits must ensure a constant-current output; because the forward junction voltage of an LED varies only slightly during operation, maintaining a constant drive current effectively ensures a constant output power. Given the instability of power supply voltages in my country, it is essential for LED streetlight drivers to feature constant-current output capabilities, thereby ensuring consistent light output and preventing the LEDs from operating at excessive power levels.
To achieve constant-current characteristics, the driver circuit must exhibit high output impedance when viewed from the output terminals. During operation, the load current flows through this output impedance; if the driver circuit consists of a step-down, rectification, and filtering stage followed by a DC constant-current source or a general-purpose switching power supply with a series resistor, significant active power is inevitably dissipated across this impedance. Consequently, while these types of driver circuits may satisfy the requirement for constant-current output, they cannot achieve high efficiency.
