Variable microwave oven soft start circuit and method

Abstract

Provided are a variable microwave oven soft start circuit and method. The soft start circuit comprises a TL431, an R14 resistor, an R16 resistor, a C13 capacitor, a C14 capacitor, a D5 diode, a D6 diode, an R22 resistor, an R23 resistor, an R24 resistor, an R17 resistor, an R19 resistor, an R18 resistor, an R15 resistor, a C12 capacitor, a Q1 triode, an R21 resistor, an R25 resistor, a C16 capacitor, a Q2 triode, an R20 resistor and a C15 capacitor. Accordingly, the target of magnetron for performing preheating to raising power to meet the requirement of an upper computer in a short time can be achieved, the power of the magetron operates stably, an impact current generated by the magnetron due to incomplete preheating is reduced, the problem that the magnetron impacts the transformer primary side IGBT in the preheating period is effectively solved, the problem that variable frequency magnetron soft start is difficult is avoided, and then the service life of a power control board is prolonged.

Description

technical field [0001] The invention relates to a soft start circuit for changing a microwave oven and a method thereof. Background technique [0002] The working principle of the frequency conversion magnetron is as follows: the low-voltage winding of the high-voltage transformer outputs an AC voltage of about 3.4V, and the high-voltage winding outputs a high-voltage AC voltage of about 2000-4000V. Among them, the AC voltage of about 3.4V supplies power to the filament of the magnetron and heats the cathode, and the AC voltage of about 2000-4000V is rectified by a high-voltage rectifier tube, and a negative high voltage is generated after filtering by a high-voltage filter capacitor to supply power for the cathode of the magnetron. When the cathode is preheated, it starts to emit electrons and continuously moves to the anode. During the movement, the electrons are affected by the vertical magnetic field and make circular motions, and generate high-frequency oscillations in ...

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Problems solved by technology

When the magnetron is started, the temperature of the cathode does not reach 2100K, so although the high-voltage winding of the high-voltage transformer generates high voltage, the cathode still cannot emit electrons, and only an AC voltage of about 3.4V is applied to the filament to heat the cathode. The input power of the primary side of the transformer is only about 100W-150W at the initial stage of startup

And because the AC current input during the preheating process is very small, generally only about 0.2A-0.8A, it is difficult for the existing AC current sampling circuit to sample accurately, and it is difficult for the microprocessor to accurately control the current flowing into the primary side of the transformer, but the inductor current on the primary side of the transformer is It is very large, reaching about 20A-30A. If the overcurrent detection circuit is not added, it is easy to cause the IGBT switch tube to burn out due to overcurrent

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