18 October 2011
Linear led driver simplifies low power led control
Integrating a high gain NPN transistor with a 30V rated pre biased NPN output transistor, the AL5802 linear led driver from Diodes is designed to provide a simple, cost effective and low EMI solution for controlling current in up to nine low power series connected leds.
The new device features an open collector output, which is capable of operating between 0.8 and 30V, and supports 12 and 24V power supplies to deliver led currents between 20 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 minimise power losses and ensures supply voltage headroom.
According to Diodes, 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 said to be 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.
In addition, the SOT26 packaged AL5802 has an ambient temperature operating range of -40 to 125ºC, which the company says enables it to be circuit mounted very close to the leds in space limited lighting applications.
Author
Laura Hopperton
Supporting Information
Websites
http://www.diodes.com
Companies
Diodes Incorporated
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