Patent ID: 8026460

Claim:
A control circuit provided in contact with a thermostatic oven in an oven controlled crystal oscillator to control the thermostatic oven, the control circuit comprising: a heater having one end supplied with a supply voltage to generate heat; a regulator that stabilizes the supply voltage; a thermistor having one end supplied with the supply voltage via the regulator, and an other end from which a voltage according to a temperature is output with a resistance value being variable according to the temperature; an operational amplifier having one input terminal to which a divided voltage of the voltage according to the temperature at the other end of the thermistor is input, an other input terminal to which a reference voltage is input, and an output fed back to the one input terminal to amplify a difference between the reference voltage at the other input terminal and the voltage at the one input terminal; a power transistor that has a collector connected with an other end of the heater, a base to which the output of the operational amplifier is input, and an emitter grounded, and controls the generated heat of the heater; and an internal temperature detection circuit that amplifies a voltage according to an ambient temperature of the thermostatic oven inside the crystal oscillator, and outputs the amplified voltage; wherein the internal temperature detection circuit includes: a transistor that has a collector supplied with the supply voltage via the regulator, a base to which the voltage according to the ambient temperature of the thermostatic oven is input, and an emitter grounded, and amplifies the voltage according to the ambient temperature of the thermostatic oven; a resistor and a capacitor connected in parallel to the base of the transistor; and an output terminal which is provided at the collector of the transistor and from which the amplified voltage according to the ambient temperature of the thermostatic oven is output as a voltage corresponding to an internal temperature.