Linear LED drivers

Supertex has introduced CL8800 and CL8801 – sequential, linear LED drivers designed to drive long strings of low-cost, low-current LEDs in solid-state replacements for fluorescent tubes, incandescent bulbs and CFL bulbs.

Both ICs minimise driver circuit component counts, requiring just four or six resistors and a diode bridge in addition to the IC. Two to four additional components in the circuit provide transient protection, and neither capacitors nor magnetic components are required. Because the ICs are multi-stage linear current regulators, there are no high-frequency switching currents and, thus, no need for a front-end EMI filter.

The CL8800 is intended for 230 V a.c. input, while the CL8801 is for 120 V a.c. input. Luminous efficiencies of greater than 115 lm/W are achievable with both ICs. The CL8800 has six current regulator outputs while the CL8801 has four. These outputs tap a string of series parallel LEDs, and the regulators sink current at each tap and are sequentially turned on and off automatically, tracking the input sine wave voltage.

Voltage across each regulator is minimised when conducting, providing typical efficiency of greater than 90%. Output current at each tap is individually resistor-adjustable. Cross regulation, as the IC switches from one regulator to another, provides smooth transitions.

The current waveforms of both ICs can be tailored to optimise for input voltage range, line/load regulation, output power/current, efficiency, power factor, THD, dimmer compatibility and LED utilisation. Both ICs are compatible with phase dimming with the addition of an RC network.