Series AMLDL-RZ

Up to 700mA | LED Driver

www.aimtec.com

Tel: +1 514 620 2722

Toll free: + 1 888 9 AIMTEC

(924 6832)

F 051e R12.F

7 of 17

North America only

Thermal Feedback Circuit

The selection of components for the thermal feedback circuit is depends on the choice of R2 and R3 and the effectiveness of

the LED heatsink. To optimize the LED brightness control at high temperatures, the LEDs must have a sufficient thermal

extraction path, if not the reduction in drive current will not be optimal.

The thermal control threshold points are set by adjusting R2. Three values (33K, 22K, and 10K) were tested. These values

were chosen to provide thermal break points of approximately 25ºC, 40ºC, and 60ºC.

Note, that the LED drive current will not continually dim to zero – the thermal controls applying DC control to that VADJ pin

has a dimming ratio from maximum current of approximately 5:1.

Once the reduced DC level drops below the shutdown threshold of around 200mV, the LED drive current will fall to zero and

the LEDs will be off.

The slope of the current reduction is determined by the beta value of the thermistor. The larger the Beta value the sharper

will be the resultant current control response. The slope of the current reduction is also affected by Q1’s base emitter voltage

variation with temperature.

AMLDL-RZ

-Vin

VADJ

+Vout

1

1

-Vout

GND

1

10K

Last LED

Q1

1

R1

4.7K

R2

10K

R3

10K

Thermistor

B 3900

BZX284C6V2

+Vin

+Vin

Thermally Connected