Datasheet

www.microchip.com/lighting LED Lighting Solutions Design Guide 19
LED Lighting Solutions
Voltage Output Temperature Sensors
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.
MCP9700/9700A
MCP9701/9701A
123
1
VDD
VOUT
GND
Bottom
View
5-Pin SC-70
3-Pin TO-92
MCP9700/9701
Only
VDD
VOUT
GND
NCNC
MCP9700/01 Voltage Output Temperature Sensors
Power LED Thermal Control Circuit Using
MCP9700 and MCP1650
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.
Learn More
The Intelligent Power Supply Design Center
(www.microchip.com/power) features temperature sensing
solutions, including application notes and product selection
charts.
Literature on the Web
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DG4 – Temperature Sensor Design Guide, DS21895
Boost Converter
SHDN
Vcc
GND
GP0
AN1
GP2
GP3
User Interface
Communication
PWM
Power
Control
MCP1650
PIC10F220
VOUT
VCC
GND
MCP9700
Temperature
Sensing
High Power
LED Module
Power LED Thermal Control Circuit Using MCP9700 and MCP1650