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Linear LED driver from Diodes Incorporated simplifies low power LED control

18th October 2011

ES Admin

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Integrating a high gain NPN transistor with a 30V rated pre-biased NPN output transistor, the AL5802 linear LED Driver from Diodes Incorporated provides a simple, cost effective and low EMI solution for controlling current in up to 9 low power series-connected LEDs. With an open collector output capable of operating between 0.8V to 30V, the SOT26 packaged driver will support 12V and 24V power supplies and deliver LED currents between 20mA to 100mA for LED signs, lamps and automotive interior display applications.

The LED current is set via an external low value resistor, the one additional component required by the driver. By generating a reference voltage of 0.65V across the resistor, the internal high gain transistor helps minimize power losses and ensures supply voltage headroom. The negative temperature coefficient of the reference voltage means that LED current is automatically reduced at high temperatures, thereby helping to protect LEDs and improve circuit reliability.

PWM dimming of the LED string is also simple to achieve by either driving the device bias pin with a low impedance voltage source or driving its enable pin with an external open collector NPN transistor or open drain N-Channel MOSFET. The AL5802’s wide ambient temperature operating range of -40ºC to +125ºC enables it to be circuit mounted very close to the LEDs in space limited lighting applications.