[PDF] What is AND8109 DATA? (812082)

The AND8109 is LED Constant Current Source Scheme made by On Semiconductor.

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AND8109 D LED Constant Current Source Scheme Theory of Operation Prepared by Mark Scholten Senior Applications Engineer http onsemi com The LM317L wants to see 1 25 V between its VOUT pin and the Vadj pin and it will do whatever it can to keep that voltage differential between them So if a resistor is put in series with the output and the Vadj pin is connected to the load side of the sense resistor a current source is set up which follows Equation 1 1 25 IOUT Approximately Rsense eq 1 But what if a series parallel combination of LEDs is wanted The following circuit works fine assuming that there are not large variations in the forward voltage drop of the LEDs There could be a problem however if one of the strings opens up for some reason The LEDs that remain would have 50 more current flowing through them which could cause them to be driven too hard and fail So how does one get around this problem VIN LM317L VOUT Rsense IOUT LED1 Vadj LED4 LED7 VIN LM317L VOUT Rsense IOUT Vadj Rload LED2 LED5 LED8 LED3 LED6 LED9 Figure 1 Figure 3 In order to set up a constant current source for an LED string the same circuit can be used by simply substituting Rload with an LED string as shown below VIN LM317L VOUT Rsense LED1 Vadj IO

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One of the primary functions of an LED driver is to ensure that the LEDs receive a constant current, which is necessary for maintaining consistent brightness and color temperature. To achieve this, many LED drivers use pulse-width modulation (PWM) to control the current flowing to the LEDs, allowing for precise regulation and dimming.

Manufacturers : On Semiconductor