Magnetron driving power supply circuit

#The present invention relates to a magnetron driving power supply circuit in an electronic range and more particularly to a magnetron driving power supply circuit of the small, light inverter type for the use of the electronic range in commercial power sources with commercial voltages (AC 110 V/220 V) and frequencies (50/60 Hz).

#In electronic ranges, there have been conventionally used the magnetron driving power supply circuits of the ferro-resonance transformer type wherein a ferro-resonance transformer may be used and the inverter type wherein a high voltage may be obtained by switching a boosting transformer at high speed.

#FIG. 1 is a schematic diagram of the conventional magnetron driving power supply circuit of the ferro-resonance transformer type. As shown in the drawing, the magnetron driving power supply circuit comprises a ferro-resonance transformer T1 having its primary coil connected to a commercial power source (AC) via a switch SW1 and its secondary coil connected to a magnetron MGT via a high voltage condenser C1 and a high voltage diode D1. This circuit constitutes a half-wave voltage doubler rectifier circuit which doubles output voltage from the secondary coil during half cycles and supplies the doubled voltage to the magnetron MGT.

#The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

#FIG. 1 is a schematic diagram of a conventional magnetron driving power supply circuit of the ferro-resonance transformer type;

#FIG. 2 is a schematic diagram of a conventional magnetron driving power supply circuit of the inverter type;

#FIG. 3 is a schematic diagram of a magnetron driving power supply circuit of the present invention. As shown in the drawing, the magnetron driving power supply circuit of the present invention comprises an input power rectifying means 11 including a noise stopping coil L1 for inputting AC power from a commercial power source (AC) and stopping noise of the AC power, and a bridge diode BD11 for rectifying the noise-stopped output power from the noise stopping coil L1. The supply circuit also comprises a variable smoothing means 12 including a relay switch RY11 and condensers C11 and C12 for smoothing the rectified output power from the input power rectifying means 11 depending upon switching states of the relay switch RY11, a capacity of each condenser varying with switching states of the relay switch RY11, a magnetron driving means 13 including a magnetron MGT having a filament, an overcurrent stopping choke coil L2 for inputting the smoothed DC power from the variable smoothing means 12 and stopping overcurrent of the DC power, and a resonance condenser C3 for inputting the overcurrent-stopped output power from the overcurrent stopping choke coil L2 and resonating the power. The supply circuit also comprises a high voltage transformer T11 having its primary coil N11 for inputting the smoothed DC power from the variable smoothing means 12 and resonating the power in association with the resonance condenser C3. One secondary coil N13 and its other secondary coil N12 of the transformer T11 are present for outputting the self-induced voltage to the filament of the magnetron MGT, and in conjunction with a high voltage condenser C1 and a high voltage diode D1 constitute a half-wave voltage doubler rectifier circuit which doubles high voltage output from the secondary coil N13 of the high voltage transformer T11 during half cycles and supplies the doubled voltage to the magnetron MGT to drive the magnetron MGT. The supply circuit also comprises a high speed switching means 14 including a switching transistor driver 14a for outputting a switching drive signal and a switching transistor Q1 responsive to the switching drive signal from the switching transistor driver 14a for being switched at high speed to control DC power supplied to the primary coil of the high voltage transformer T2 and the resonance condenser C3, and a low voltage transformer T22 for inputting AC power from the commercial power source (AC) and dropping the AC power, the low voltage transformer T22 having a primary coil N21 and secondary coils N22 and N23. The supply circuit also comprises a low voltage rectifying means 16 including a bridge diode BD12 for rectifying output power from the secondary coil N22 of the low voltage transformer T22, a low voltage smoothing means 17 including a relay switch RY12 and condensers C13 and C14 for smoothing the rectified output power from the low voltage rectifying means 16 depending upon switching states of the relay switch RY12, the capacity of each condenser varies with switching states of the relay switch RY12. The supply circuit also comprises a relay driving means 19 including a relay RY1 adapted to open/close the relay switches RY11 and RY12 of the variable switching means 12, a diode D11 rectifying AC power inputted from the secondary coil N23 of the low voltage transformer T22, a condenser C15 smoothing the output from said diode D11, and a zener diode ZD11 adapted to control the drive of said relay RY1. The supply circuit also comprises a voltage level detecting means 20 including a diode D12 rectifying the output voltage of the low voltage smoothing means 17, a condenser C17 smoothing the output from said diode D12, a variable resistor VR11 and a resistor R12 dividing the smoothed output from said condenser C17, and a voltage detector 20a detecting the divided voltage. The supply circuit also comprises a current level detecting means 15 including a current detector 15a and a current transformer CT detecting current flowing according to the switching of the high speed switching means 14, a constant voltage output means 18 including a transistor Q11 receiving at its collector and base the output voltage of the low voltage smoothing means 17 and a zener diode ZD12 receiving the output voltage of the low voltage smoothing means 17 through a resistor R11, and a condenser C16, in order to output a constant voltage, and a control circuit means 21 including a microprocessor 21a receiving the output voltage of said constant voltage output means 18 as the operating voltage and applying a switching drive control signal to the switching transistor driver 14a of the high speed switching means 14 in response to detecting signals of the voltage level detecting means 20 and the current level detecting means 15.

#FIG. 4 is a detailed diagram of the control circuit means 21 shown in FIG. 3. As shown in the drawing, the control circuit means 21 comprises a microprocessor 21a having input terminals I1 and I2 to which detected signals from the current level detector 15 and the voltage level detector 20 are applied, respectively, The control circuit means 21 also comprises transistors Q12 to Q14 having bases connected to output terminals P1 to P3 of the microprocessor 21a via resistors R12 to R14, respectively. The transistors Q12 to Q14 also have collectors connected, via resistors R16 to R18, respectively, to the inverting input terminal (-) of a comparator CP11 and a resistor R15 which is connected to a voltage source terminal Vcc of the control circuit means 21. At ON state, the transistors Q12 to Q14 apply different levels of reference voltage to the inverting input terminal (-) of the comparator CP11. A triangular wave generator 21b is connected to the non-inverting input terminal of the comparator CP11, thereby causing its output signal to be applied to the comparator CP11 as a comparative signal. The output terminal of the comparator CP11 is connected to the switching transistor driver 14a of the high switching means 14, so that square signal of high frequency from the comparator CP11 can be applied to the switching transistor driver 14a, as a switching drive control signal.

#Now, the operation of the circuit of the present invention will be described in detail.