The Study And Design Of A Constant Power Control Circuit With Temperature Correction

With the steady improvement of people's living standards and electronic information technology,the demand and opportunities of portable electronic products are increasing day by day.At the same time,people's requirements for functional integrity,performance consistency and quality reliability of portable electronic products are also increasing.Especially in the field of gas and liquid sensors,where heating and atomizing circuits are becoming hot spots.This circuit can be widely used in electronic medical nebulizers,ladies beauty moisturizing sprays,electronic cigarettes,etc.At this stage,the circuit has output power supplied by batteries.The output power can not be constant because of voltage and heating wire resistance change,and there is no effective temperature monitoring and control mechanism.Therefore,the circuit design needs to produce excellent atomization effect,and it is required to ensure product safety and reliability.According to the existing problems and requirements,the circuit designed in this paper has the following functions:1.The output power of the circuit does not change with the voltage drop of the lithium battery,ensuring that the output power is kept constant throughout the power supply range of the lithium battery;2.The output power does not change with the resistance value of the heating wire,which means the resistance change caused by the temperature rise or the replacement of the heating wire will not affect the output;3.The output power of the circuit can be adjusted by an external power control resistor;4.The temperature of the heating wire can be detected in real time and adjusted when it is over temperature.In order to meet the above functional requirements,this thesis designs and implements a constant power control circuit with temperature compensation.After the circuit is powered up,the temperature of the heating wire rises rapidly to the normal operating point,and the circuit performs the constant power output mode.At this time,the voltage and current values at the heating wire are obtained by real-time sampling,and the power is calculated by the internal multiplier and determined by the power regulating resistor.Set the power to compare and adjust the PWM duty cycle of the output control signal so that the output power remains constant.At the same time,through the combination of the thermistor around the heating wire and the EA,the temperature of the heating wire is reflected in the current detection in real time.When the over-temperature occurs,the sampling current increases,and the system rapidly changes the duty ratio of the output control signal by reducing the output power.The temperature of the heating wire is corrected to the normal working temperature range,and the use risk due to temperature rise is prevented,and the internal detection and calculation module is not required while the temperature correction effect is achieved,thereby reducing the pressure of the chip layout.In this thesis,the cadence tool is used to design the road,the simulation is carried out by hspice,the layout is designed by Virtuoso,and the layout is verified by Calibre.The designed circuit is designed and implemented based on the 0.18 um BCD process.The circuit mainly includes five main circuit modules: bandgap reference source circuit,current voltage sampling module,analog-to-digital conversion module,power control module and temperature detection and feedback.The bandgap reference source and current mirror are used to generate the voltage and current reference required by each module.The Cascode structure is used to make the output of the current source more stable to ensure the accuracy of the analog-to-digital converter output.After the simulation of the circuit module is confirmed,the whole circuit is simulated and the system test is performed after the IC is released.The test result is consistent with the simulation result,and all the above four design functions can be verified,that is,the output power of the system is adjustable,and It does not change with the voltage condition of the lithium battery or the resistance value of the heating wire,and the temperature of the heating wire can be detected and corrected in real time.