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Maxim > Design Support > Technical Documents > Application Notes > Temperature Sensors and Thermal Management > APP 2010
Keywords: temperature switch, thermal switch, temperature protection, thermal disconnect, over-temperature
proctection, temp protection, temp switches
APPLICATION NOTE 2010
Thermal Switches Provide Circuit Disconnect
Jun 20, 2003
Abstract: A pair of temperature switches control a thermal disconnect circuit for system temperature protection.
The circuit "crowbars" the power supply when excessive temperature is detected by the thermal switches.
A temperature sensor can provide an interrupt to a microcontroller when the measured temperature goes out
of range. The microcontroller implements the proper protective action when one of the temperature monitors
detects an over temperature condition. But sometimes it is easier and more cost effective to simply disconnect
the offending circuit from the power supply without getting a microcontroller involved.
Multiple temperature sensors are needed when more than one hot spot needs to be monitored. A simple
thermal-protection circuit (Figure 1) includes two temperature switches (U1 and U2) with active-high outputs.
Temperature thresholds for these switches are set by resistors R1 and R2, and the switch outputs connect to
the inputs of a dual-input OR gate (U3). OR gates with more than two inputs are available if more than two
temperature switches are needed. When excessive temperature drives either input high, the OR-gate output is
driven high, causing a silicon controlled rectifier (SCR) to crowbar the power supply and blow the fuse.
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