String LED circuit diagram Constant Current Power Supply

The LM3466 integrates a linear LED string driver circuit diagram for lighting systems which consist of multiple LED strings powered by a constant current power supply. An ideal constant current power supply delivers a constant current (IS) regardless of the output voltage of the connecting load. In the lighting system, each device regulates the current of an LED string. The current IS provided by the supply is balanced (i.e. shared in a pre-set ratio determined by a single resistor) through each active LED string automatically, regardless of the number of strings connected to the supply or the forward voltage of each string. Here, an active LED string refers to a fully turned on LED string.

If any LED string opens during operation, the LED current of all remaining active LED strings will increase to balance the current provided by the supply automatically. As a result, the total output power remains nearly the same in case of the decrease of active LED strings. This gives an advantage that the overall brightness of the lighting system is maintained even if some LED strings open during operation.

A LM3466 lighting system is simple to design owing to a proprietary control scheme. To minimize the component count, the LM3466 integrates a 70-V, 1.5-A, N-channel MOSFET with a current limit of 2.06 A. To add one more LED string to the system, only a single resistor, a capacitor, and an additional LM3466 device are required. Other supervisory features of the LM3466 include under-voltage lock-out, fault reporting, thermal latchoff, and thermal shutdown protection.

APPLICATIONS • Street Lamps • Solid State Lighting Systems Wide Input Voltage Range from 6 V to 70 V  Thermal Shutdown EMI standards.  Integrated 70-V, 1.5-A MOSFET with 2.06 A  Current Limit  Maximum 70-V per LED String, 20 LEDs • Linear Circuitry Does Not Deteriorate EMI

Download source: LM3466 - Texas Instruments     http://www.ti.com/lit/ds/symlink/lm3466.pdf