The induction cooker uses the principle of high frequency induction to realize heating. By inputting high frequency voltage to the heating coil, eddy current is generated in the pot to realize heating. Therefore, the induction cooker needs a part of the circuit to convert the input power frequency AC voltage into high-frequency voltage to drive the heating coil. This part of the circuit is the main power circuit of the induction cooker. In addition to the drive circuit of the coil, there are many detection, control and protection circuits in the induction cooker. These circuits are used to assist in controlling the heating, protecting the abnormal parameters and controlling the operation.
The basic working principle of the main power circuit of the induction cooker is actually similar to that of the switching power supply. After the 220V AC voltage is input, it will first be rectified by the diode into a DC voltage, and then filtered by the capacitor into a voltage of about 310V. This voltage will enter the heating coil after passing through the switch tube, and the drive circuit will control the switch tube to turn on and off, The formed high-speed switch changes the DC voltage into high-frequency pulsating DC voltage. The pulsating DC voltage is the same as the AC voltage. Their function is to generate the magnetic flux change of the coil, so that the corresponding current can be sensed on the pot to realize heating.
After completing the basic heating control, a part of auxiliary detection circuit is required to detect the parameters in the main circuit, but when the detected parameters are abnormal, it will control the shutdown for protection. The detection circuit in the induction cooker generally includes the detection of voltage, current and temperature. The voltage detection mainly refers to the grid voltage and the coil voltage. When the grid voltage is detected to be too high or too low, the system will control the shutdown. When the reverse peak voltage of the coil is detected to be too high, the system will also control the shutdown. The voltage detection is mainly used to protect the switch tube and control circuit.
The current detection is mainly used to sample the current in the main power circuit, which has three main functions: the first function is to judge the current power by detecting the current in the circuit, so as to form feedback control with the set power; The second function is overcurrent protection. When the current in the circuit exceeds the set value due to coil or switch tube problems, the switch element is controlled to turn off the protection; The third function is to detect pots and pans. When the pots and pans used are of unsuitable material or too small area, the current in the current circuit cannot meet the set minimum current requirements, which will also control the off output. This is mainly to prevent the waste of electric energy, but also to reduce certain high-frequency radiation.
The temperature detection of induction cooker generally uses NTC, which is a thermistor with negative temperature coefficient. It is a resistance that decreases with the increase of temperature. The temperature detection is mainly at the bottom of the pot and the power tube. The thermistor detected at the bottom of the pot is usually placed in the middle of the coil and contacts the ceramic plate through the thermal conductive silicone grease. When the temperature of the pot is detected to be too high, the power is cut off in time, mainly to prevent dry burning. The power tube will generate heat because of the voltage drop when it is turned on. In addition to cooling through aluminum fins, it also uses fans for auxiliary cooling. When it detects that the temperature is too high, cutting off the power supply is mainly used to protect the power tube. Other circuits of the induction cooker are mainly the control of buttons and displays, the delay control of fans, etc.
