Patent ID: 8605403

Claim:
A thermal protection circuit for an electronic device, comprising: a temperature sensor operable to sense an internal temperature of the electronic device and output an internal temperature signal with a voltage, wherein the voltage of the internal temperature signal is inversely proportional to the internal temperature; a hysteresis comparator to output a power-off signal when the voltage of the internal temperature signal is lower than a low voltage threshold representing a determined temperature, or output a power-on signal when the voltage of the internal temperature signal is higher than a high voltage threshold representing a restarting temperature of the electronic device; a switch circuit to stop transmitting power signals to the electronic device in response to the power-off signal, or continue to transmit the power signals to the electronic device in response to the power-on signal; wherein the hysteresis comparator comprises: a zener diode with an anode grounded, wherein a voltage of the zener diode is greater than a voltage of the power signals; a second voltage division circuit connected between a second reference voltage and a cathode of the zener diode, the second voltage division circuit comprising a second resistor and a third resistor connected in series; an operational amplifier comprising an inverting input to receive the internal temperature signal, a non-inverting input connected to a common node of the second resistor and the third resistor of the second voltage division circuit, and an output connected to the cathode of the zener diode and outputting the power-on signal and the power-off signal; wherein an upper triggering voltage and a lower triggering voltage of the hysteresis comparator are respectively defined as the high voltage threshold and the low voltage threshold; and wherein the upper triggering voltage is calculated by U P1 =U 2 ×R 2 /(R 2 +R 3 )+UZ×R 3 /(R 2 +R 3 ), where U P1 represents the voltage of the upper triggering voltage, U 2 represents a voltage of the second reference voltage, U Z represents the voltage of the zener diode voltage, R 2 and R 3 represent resistances of the second resistor and the third resistor, respectively.