JPS6361751B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high frequency heating device equipped with a gas sensor, and more particularly to the configuration of a constant voltage power supply for an indirect heater of a gas sensor.

Conventional configuration and its problems In order to automatically terminate microwave heating, high-frequency heating devices equipped with gas sensors that detect water vapor and various gases generated from the heated object are widely used in practical use. . An example of such a gas sensor is the relative humidity sensor "Hyumi Ceram" manufactured by Matsushita Corporation.
, the absolute humidity sensor ``Neo-Hyumi Ceram,'' and the gas sensor manufactured by Figaro are being applied. All of these sensors are equipped with an indirect heater to indirectly heat the sensor chip to a predetermined temperature to develop the desired sensing characteristics and to burn off any dirt on the chip.

FIG. 2 shows a typical configuration example of such a conventional indirect heater circuit for a gas sensor. A rectifier diode 6 and a smoothing capacitor 7 are connected to the secondary winding of the transformer 5, and a DC voltage is formed at point _P1 . The voltage is then made constant by the transistor 8 and applied to the indirect heater 9 of the gas sensor. The reference voltage of the transistor 8 is created by a Zener diode 10, and the Zener current is supplied from a point _P1 through a resistor 11. Diode 12 improves temperature characteristics.

Although such a constant voltage power supply has a generally popular configuration as a power supply, it has the disadvantage that the power supply becomes large-scale for a low-voltage, large-current type load such as an indirect heater. For example, in Matsushita's "Neo Huyumi Ceram", the indirect heater is 2.5 volts and 0.5 ampere (1.25 watts), but the smoothing capacitor 7 must be made considerably large, or the rectifier diode 6 must be changed from half-wave rectification to full-wave rectification. If no changes are made, the ripple at the _P1 point will become too large, and the Zener voltage will also be affected, causing ripples to appear at both ends of the indirect heater 9. To give an example, when the specifications of the secondary winding of the transformer are 5 volts and 1 ampere, and when half-wave rectification is used, the smoothing capacitor 7 must be at least 3300 microfarads or ripples will occur at both ends of the indirect heater 9. .

As described above, the conventional constant voltage power supply has the problem that the circuit is large-scale and a large-capacity smoothing capacitor is required.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a compact and inexpensive power source for an indirect heater of a gas sensor.

Configuration of the Invention In order to achieve the above object, the high frequency heating device of the present invention includes a gas sensor and a plurality of constant voltage power supplies,
The reference voltage of the constant voltage power supply connected to the indirect heater of the gas sensor is created from a different constant voltage power supply, and the power supply can be configured compactly and at low cost.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 is a perspective view of a high-frequency heating device according to the present invention. A door body 2 is pivotally supported on the front surface of the main body 1 so as to be freely openable and closable, and an operation panel 3 is provided. On this operation panel 3, there is arranged an auto key that performs automatic heating using a gas sensor.

FIG. 3 shows a power supply according to an embodiment of the present invention. The indirect heater 9 of the gas sensor is connected to a constant voltage power source as in the conventional example shown in FIG. What is different from the conventional one is the Zener that creates the reference voltage for transistor 8.
A resistor 11 that supplies current to the diode 10 is
This point is connected not to the point _P1 but to the output terminal _P2 of another constant voltage power supply 13. This constant voltage power supply 13 is also used for other purposes, such as supplying a power supply voltage to a control section 14 implemented by a microcomputer, etc., and also applies a reference voltage to a gas sensor chip 15 and an input resistor 16. This _P3 point is connected to the A/D input.

With this configuration, no ripple occurs at point _P2 , so the Zener voltage of the Zener diode 10 is stable even when a large current flows through the indirect heater 9, and ripples are less likely to occur in the output of the transistor 8. For example, if the specifications of the secondary winding of transformer 5 are 5 volts and 1 ampere, and when half-wave rectification is used, connect Matsushita's "Neo Huyumi Ceram" (2.5 volts, 0.5 ampere), and the smoothing capacitor is 2000 microns.・If I had Furatsudo, I could eliminate Ripple.

FIG. 4 is a circuit diagram showing still another embodiment of the present invention, in which the reference voltage of the transistor 8 is created by resistance division using a voltage follower of an operational amplifier 17. The reference voltage is formed by dividing the potential +B at point _P2 by resistors 18 and 19. With this configuration, a low voltage of 2.5 volts can be stably generated, and variations in heater voltage can be suppressed compared to a method using a Zener diode. Furthermore, even if the voltage +B varies, it is well fed back to the heater voltage, and the potential at point _P3 becomes stable.
For example, if the +B voltage varies to a high degree, P ₃
The potential at point P3 also tends to move higher, but the heater voltage also increases, the temperature of the chip 15 increases, the resistance value decreases, and the potential at point _P3 can be prevented from moving higher.

FIG. 5 shows the configuration of such a high frequency heating device.
Commands input from the auto key 4 on the operation panel 3 are decoded by the control section 14. The control unit 14 then starts supplying power to the magnetron, which is the high frequency generating means 21, via the driver 20. An object to be heated 23 is placed on a placing plate 24 in the heating chamber 22 . The mounting plate 24 is rotationally driven by a motor 25 to improve uneven heating.

As the heating progresses, steam and gas begin to be generated from the heated object 23. This water vapor is discharged to the outside of the aircraft from an exhaust guide 27 by a fan 26, and a gas sensor 15 is disposed here. The gas sensor 15 is connected to the A/D converter of the control section 14 via a detection circuit 28 shown in FIG. 3 or 4. The control unit 14 can be realized by a microcomputer with a built-in A/D converter.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained.

(1) It is possible to eliminate ripples and stably configure the constant voltage power supply for the indirect heater of the gas sensor, which is difficult to use due to the low voltage and large current.

(2) It can be configured more compactly and inexpensively.

(3) Fluctuations in the input voltage of the sensor chip can be suppressed by feeding back the heater voltage.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the main body of a high-frequency heating device showing an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional indirect heater of a gas sensor, and FIG. 3 is a diagram of a gas sensor showing an embodiment of the present invention. FIG. 4 is a circuit diagram of an indirect heater showing another embodiment, and FIG. 5 is a block diagram showing the same configuration. 8... Constant voltage transistor, 9... Indirect heater, 10... Zener diode, 13... Second constant voltage power supply, 14... Control unit, 15... Gas sensor chip, 21... High frequency generation means, 22
...Heating chamber, 23...Object to be heated.

Claims (1)

[Claims] 1. A heating chamber in which an object to be heated is placed, a high-frequency generating means coupled to this heating chamber, a control section for controlling power supply to this high-frequency generating means, and a device for detecting water vapor and gas generated from the object to be heated. a constant voltage power source connected to an indirect heater of the gas sensor, and a reference voltage of the constant voltage power source is configured from a second constant voltage power source different from the reference voltage of the constant voltage power source,
A high-frequency heating device that connects the lines of both constant-voltage power supplies to have the same potential.