Microchip Technology APGRD004 Data Sheet

www.microchip.com/lighting 

LED Lighting Solutions Design Guide

         

   

The most basic technique employed to protect the device 
from damaging over-temperature conditions is to provide 
a shutdown signal to the driver circuit when a pre-defined 
threshold is reached. However, this behavior can be 
unacceptable in applications where continuous lighting 
is required for safety or regulatory conditions. A more 
advanced approach can be obtained if a microcontroller is 
used to manage the lighting application providing closed 
loop control of the power supplied by the driver circuit. 
As the temperature approaches the threshold the current 
supplied can be reduced to limit the power output.

By using a Voltage Output Temperature Sensor such as 
the MCP9700 and MCP9701, placed on the LED module 
close to the emitting device, it is possible to provide a 
linear voltage feedback signal to a PIC microcontroller. This 
solution ensures that the light source can always operate at 
a power level that remains within temperature limits. Almost 
any kind of software algorithm can be implemented in the 
microcontroller to respond to the temperature feedback, 
allowing tremendous flexibility.

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V

DD

V

OUT

GND

Bottom

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V

DD

V

OUT

GND

NC

NC

Alternatively a PIC microcontroller can perform a direct 
PWM control (on/off) of the entire LED driving circuit at low 
frequency (100-120 Hz). By limiting the average
on-time of the power LED, the total power output can be 
limited. This technique has the advantage of stabilizing the 
application temperature while maintaining the LED driving 
current constant therefore limiting the LED color shift 
produced by forward current changes. The diagram below 
illustrates an example of a switching DC-DC converter design 
based on the MCP1650 boost regulator controlled by a 6-pin 
PIC10F220 microcontroller.

The Intelligent Power Supply Design Center
(

www.microchip.com/power

) features temperature sensing 

solutions, including application notes and product selection 
charts.

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DG4 – Temperature Sensor Design Guide, DS21895

User Interface

Communication

PWM
Power
Control

Temperature

Sensing