Driver thermally compensates LED


Posted on Nov 18, 2012

The circuit in Figure 1 allows you to compensate for both of these temperature-dependent problems, using only the TSF-102 sensor from Texas Instruments (www.ti.com). The device is a temperature-dependent positive-temperature-coefficient resistor with a linear temperature coefficient of approximately 0.7%/°C at 25°C. For the circuit in Figure 1, you must thermally couple the sensor with the LED. IC2 is a summing amplifier for the input voltage and the reference voltage from IC3. The gain is -1 and increases with temperature. The temperature-independent -VREF drives the base of transistor Q2. The thermally stable current source, Q3, via the differential pair Q1-Q2, supplies the LED. Note that you should mount Q3, D, and DZ on a common heat sink.






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