Working Principle of Current Transformer Sampling Circuit
The current sampling unit is a sampling circuit that provides the current sampling signal to the single chip microcomputer when the induction cooker works. The single chip microcomputer always detects the change of the input current, and automatically adjusts the PWM signal according to the detected current sampling signal to make the induction cooker do the constant processing of the output power. The single chip microcomputer will also detect the input current of the induction cooker according to the change of the detected current sampling signal, so as to automatically make various actions. When the single chip microcomputer detects the appropriate pulse number of the pot in the synchronous circuit, it will use 0.5 2S to detect the change of the current, and determine whether the material and heating area of the heating pot meet the heating requirements through the difference of the current change. When the current sampling signal changes too much, the single chip microcomputer will judge whether there is no pot. There are two common current sampling unit circuits in the mainstream induction cooker circuits in the market, namely, the current sampling unit using current transformer sampling and the current sampling unit using resistance voltage drop sampling. The working principles of these two sampling circuits will be introduced below.
The current sampling unit is a sampling circuit that provides the current sampling signal to the single chip microcomputer when the induction cooker works. The single chip microcomputer always detects the change of the input current, and automatically adjusts the PWM signal according to the detected current sampling signal to make the induction cooker do the constant processing of the output power. The single chip microcomputer will also detect the input current of the induction cooker according to the change of the detected current sampling signal, so as to automatically make various actions. When the single chip microcomputer detects the appropriate pulse number of the pot in the synchronous circuit, it will use 0.5 2S to detect the change of the current, and determine whether the material and heating area of the heating pot meet the heating requirements through the difference of the current change. When the current sampling signal changes too much, the single chip microcomputer will judge whether there is no pot. There are two common current sampling unit circuits in the mainstream induction cooker circuits in the market, namely, the current sampling unit using current transformer sampling and the current sampling unit using resistance voltage drop sampling. The working principles of these two sampling circuits will be introduced below.
(1) The current sampling unit using current transformer sampling is shown in figure (a) below. The AC voltage secondary measured by current transformer CT1 is rectified by bridge rectifier composed of d10 D13. The DC voltage smoothed by EC5 is sent to the I-A / D port of CPU, and CPU detects the input current of induction cooker according to the change of this voltage signal. The turn ratio of current transformer CT1 is 1:3000. If the turn ratio is large, the induced current is linear when working with high current. VR1 is an adjustable resistance of 0 10K , which is mainly used to adjust the power deviation caused by structural error. It can also change the reference of current detection by adjusting this resistance to achieve the purpose of adjusting the output power of induction cooker. When the VR1 resistance increases, the voltage of the corresponding current detection will increase. When the primary current of CT1 is constant, the voltage induced by the secondary of CT1 will increase accordingly. The program will control accordingly according to the change of analog signal of a / D port. According to the requirements of software constant power, the power will decrease relatively.
Transfer files for [membrane switch] proofing
