Single limit comparator circuit made with LM339

Figure a shows a basic single-limit comparator. The input signal Uin, i.e. the voltage to be compared, is added to the non-inverting input terminal, and a reference voltage (threshold level) Ur is connected to the inverting input terminal. When the input voltage Uin>Ur, the output is a high level UOH. Figure b shows its transmission characteristics. The figure
 
 below shows an overheat detection protection circuit in a certain instrument. It is powered by a single power supply, and a fixed reference voltage is added to the inverting input terminal of 1/4LM339, and its value depends on R1 and R2. UR=R2/(R1+R2)*UCC. The voltage at the non-inverting terminal is equal to the voltage drop of the thermistor Rt. When the temperature inside the machine is below the set value, the voltage at the "+" terminal is greater than the voltage at the "-" terminal, and Uo is a high potential. When the temperature rises above the set value, the voltage at the "-" terminal is greater than the "+" terminal, the comparator reverses, and the Uo output is zero potential, which activates the protection circuit. Adjusting the value of R1 can change the threshold voltage, that is, the size of the set temperature value.