Used as a protective circuit above uses a component named PTC , the components in the operating obstacles , but obstacles desert PTC component is influenced by temperature, whereby if the cold temperatures of less than 100 degrees celcius , then this component has a few obstacles. And when temperature run to 100 degrees celcius or higher, which is owned PTC resistance will rise ass well. Because it depends on ambitient temperature , the PTC can be assembled into a circuit protection if high ambitient temperature, tand automatically switchess off, circuit like a schematic above. Part List : R1___4K7 R2___10K R3___1K9 R4___1M R5___4k7 TH1__PTC thermistor IC____LM393