JPH03173093A - Power control of magnetron power supply - Google Patents

Abstract

PURPOSE:To make fluctuation of input power smaller as against fluctuation of anode voltage to guarantee stable action by controlling an anode current to impressed voltage between an anode and a cathode by means of the specific relation. CONSTITUTION:When voltage to be impressed on an anode of a magnetron 3 is expressed by Eb, an anode current Ib shall be controlled by the following formula: Ib=b.(a-Eb). Here, a = a marginal voltage setting constant between the anode and cathode, while b = a power variable constant. Even when, accordingly, the anode voltage Eb fluctuates at the time of normal operation round the average anode voltage as a center, input power is suppressed to slight fluctuation toward the set input power so that stable operation is guaranteed. Even when, therefore, the anode voltage fluctuates round the average anode voltage as a center, the input power is suppressed to slight fluctuation toward the set input power thus to guarantee stable operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a power control method for a magnetron power supply, such as an inverter power supply for a microwave oven.

(Prior Art) In general, a magnetron has the characteristic that during normal operation, the magnetron outputs microwaves without changing much around a constant voltage where the anode-cathode voltage (hereinafter simply referred to as anode voltage) is formed. There is. By the way, during operation of the magnetron, unstable operation such as moding may occur due to low emission or the like. When moding or the like occurs, if power continues to be supplied from a power source such as an inverter, the anode voltage becomes extremely high, leading to dielectric breakdown or the like.

Conventional techniques to deal with this problem include providing a circuit that monitors the limit voltage of the anode voltage in addition to the power control circuit for controlling the input power to the magnetron, or increasing the withstand voltage of the circuit to which the anode voltage is applied. measures were taken.

(Problem to be Solved by the Invention) In order to protect the magnetron, etc. from excessive anode voltage when moding occurs, conventionally a circuit for monitoring the limit voltage of the anode voltage has been provided separately from the power control circuit. Alternatively, measures were taken to increase the withstand voltage of the circuit to which the anode voltage is applied. For this reason, there was a problem of high cost.

Therefore, this invention is inexpensive and guarantees stable operation by reducing fluctuations in human power in response to fluctuations in anode voltage during normal operation, and also reduces the anode voltage below the limit voltage when moding occurs. It is an object of the present invention to provide a power control method for a magnetron power source that can reliably suppress the power consumption.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the first invention provides that, when the voltage applied between the anode and cathode of the magnetron is Eb, the anode current Ib is expressed by the following formula. (1 formula %) However, the gist is that a: limit anode-cathode voltage setting constant b - power variable constant.

Further, the second invention detects the voltage applied between the anode and cathode of the magnetron with a voltage detection means, detects the anode current of the magnetron with the current detection means, and detects the set digital value and the voltage applied to the reference terminal or A multiplication type D/ that multiplies the current value and outputs the product as an analog value.
The A converter multiplies the set digital value by the anode current detection value detected by the current detection means,
The output value of the multiplication type D/A converter and the anode-cathode voltage detected by the voltage detection means are added by an addition means to which a predetermined reference voltage is set, and the control means is controlled based on the output of the addition means. The gist is to control the anode current by.

(Function) In the first invention, the anode current Ib is I b−b ·
Since it is controlled based on the equation (a-Eb), the input power P of the magnetron follows the following equation.

As a result, set the power variable constant to an appropriate value, and assume that the withstand voltage (limit voltage) of the magnetron is, for example, twice the average anode voltage during normal operation of the magnetron. Then, if the limit anode-cathode voltage setting constant a is selected to the value of this limit voltage, the anode current I
b has a linear characteristic with a negative slope with respect to the anode voltage Eb, and the input power P has a maximum input power value (set input power) near the average anode voltage and becomes zero at the limit voltage, and has a convex shape. It becomes a quadratic curve characteristic. Therefore, even if the anode voltage Eb fluctuates around the average anode voltage during normal operation, the human power is suppressed to a slight fluctuation with respect to the set input power, and stable operation is guaranteed. On the other hand, even if the anode voltage Eb tends to increase due to the occurrence of moding, the anode current Eb decreases and the moding subsides, and along with this, the input power becomes zero at the limit voltage. , destruction of the magnetron, etc. is reliably prevented.

In addition, in the second invention, the control having the same operation and effect as described above is performed using voltage detection means, current detection means, multiplication type D/A
This is achieved by the control circuit itself using a converter, addition means, and control means, and there is no separate circuit for monitoring the limit voltage of the anode voltage, so it is possible to implement the power control method for the magnetron power supply at low cost. becomes.

(Example) Embodiments of the present invention will be described below based on the drawings.

First, the power control method of the magnetron power supply of this embodiment will be explained using FIG.

In this embodiment, when the voltage applied to the anode of the magnetron is Eb, the anode current Ib is controlled by the following equation.

I b-b ・(a-Eb) −(1
) Here, a - Limit anode-cathode voltage setting constant S - Power variable constant Therefore, the input power P of the magnetron is determined according to the following equation.

P-Eb-Ib -Eb-b ・(a-Eb) 1-b-Eb2+a-b -Eb ・=(2) Here, the average value of the anode voltage Eb of the magnetron used during normal operation is 4000V, The withstand voltage of the inverter output circuit, etc. (limit voltage of anode voltage Eb) is 8000.
Assuming that V, the limit anode-cathode voltage setting constant is selected as a=8000, and the power variable constant is bl,
The anode current Ib obtained by equation (1) is Ib in FIG.

It becomes a straight line with a negative slope as shown in . On the other hand, (2)
The human power P1 obtained by the formula, as shown by P in Fig. 1, shows the maximum input power value (set human power) at the average anode voltage of 4000V, and the limit voltage is gooo
It becomes an upwardly convex quadratic curve that becomes zero at v. And the anode current ■b blind straight line and the quadratic curve of input power P1 are:
Intersect at the maximum human power value.

Therefore, the anode voltage Eb is, for example, ±10% of the average anode voltage, that is, from 3600V to 4400V.
Even if the input power P1 of the magnetron fluctuates between 1 and 2, the input power P1 of the magnetron can be suppressed to a value of +0 to -1% of the set input power. In magnetrons using commonly used ferrite magnets, the temperature of the ferrite magnet increases as the anode temperature rises, and the magnetic flux generated by the ferrite magnet decreases, resulting in a tendency for the average value of the anode voltage Eb to decrease. There is. However, even in such cases,
As mentioned above, fluctuations in the input power caused by fluctuations in the anode voltage Eb are suppressed to a minimum, ensuring stable operation.

On the other hand, due to the occurrence of moding etc., the anode voltage Eb
For example, when the anode voltage Eb is 5
If the voltage increases to 000V, then the anode current Ib decreases to about 50% of that at 4000V, and the moding subsides. When the anode voltage Eb reaches the limit voltage of 8000V, the human power P blindness becomes zero,
Destruction of the inverter output circuit, magnetron, etc. is reliably prevented.

In addition, the value of the limit anode-cathode voltage setting constant is
If the power variable constant is changed to b2, which is smaller than the above bl, while keeping a-8000 as above, the anode current Ib2 becomes a straight line as shown by Ib2 in FIG.
The human power P2 becomes a quadratic curve as shown by p2. Also in this case, even if the anode voltage Eb varies between 3600V and 4400V as above,
The input power P2 is suppressed to a slight fluctuation of +0 to -1% with respect to the set input power, and stable operation is guaranteed.

Furthermore, in the case of occurrence of moding, etc., the anode current Ib decreases and the moding subsides, as described above.
Along with this, the anode voltage Eb is the limit voltage 8
Since the voltage is suppressed to 000 V or less, destruction of the magnetron, etc. is reliably prevented.

Further, when the withstand voltage of the inverter output circuit, etc. is about 6000V, which is lower than the above case, if the limit anode-cathode voltage setting constant is selected as a-6000 and the power variable constant is set as s, then the anode current Ib3 is , in Figure 1, I
The input power P3 becomes a straight line as shown by b3, and the input power P3 becomes an upwardly convex quadratic curve that becomes zero at 6000V as shown by P3.

Therefore, in this case, the variation in the human power PI with respect to the variation in the anode voltage Eb around the average anode voltage is larger than in the above two examples. but,
With respect to the occurrence of moding, the degree of decrease in the anode current Ib becomes large, so that this can be quickly controlled, and the anode voltage Eb is set to a limit voltage of 6.
000V or less, and destruction of the magnetron etc. is reliably prevented.

Next, a circuit example of an inverter control circuit for realizing the above-described power control method of the magnetron power source will be described using FIGS. 2 to 4.

In FIG. 2, reference numeral 1 denotes a commercial AC power source, for example AClooV, and this commercial AC power source 1 is connected to an inverter main circuit 2. In FIG. The output of the secondary winding of the output transformer in the inverter main circuit 2 is supplied between the anode and cathode of the magnetron 3. 4 is a voltage detection means for detecting the anode voltage Eb applied between the anode and the quad of the magnetron 3, and the detected anode voltage E
b is input to an adder circuit to be described later. 5 is a current detection means for detecting the anode current Ib of the magnetron 3, and is composed of a current transformer. As shown in the figure, the current detection means 5 detects the secondary winding current of the output transformer in the inverter main circuit 2 instead of detecting the anode (cathode) current Ib of the magnetron 3. This is because the anode (cathode) current Ib has a DC component, but the current transformer cannot detect the DC component, so not only will it not be possible to detect an accurate current value, but the DC component may saturate the magnetic core of the current transformer. There is. Therefore, the anode (cathode) current Ib
The secondary winding current of the output transformer in the inverter main circuit 2, which is correlated with the value of , is detected.

The detected value of the current detection means 5 is the multiplication type D/A converter 1.
0 reference voltage terminal (Vref terminal).

The multiplication type D/A converter 10 multiplies the set digital value by the voltage or current value applied to the reference voltage terminal,
It has a function to output the product as an analog value.
This is to realize the power variable constant in equation (1) above.

The details of the configuration of this multiplication type D/A converter 10 will be described later. The output of the multiplication type D/A converter 10 is input to an adding circuit 6 as an adding means.

In the adder circuit 6, a reference voltage Vref corresponding to the limit anode-cathode voltage setting constant a of equation (1) is set at the non-inverting input terminal (+). The addition circuit 6 has a function of adding the output value of the multiplication type D/A converter 10 and the anode voltage Eb detected by the voltage detection means 4, and subtracting the added value from the value of the reference voltage Vref. . Then, the inverter main circuit 2 is controlled by the control circuit 7 as a control means based on the output of the adder circuit 6, and the anode current Ib of the magnetron 3 is controlled.
Control corresponding to the anode current control formula shown in the equation is realized.

Next, a specific example of the multiplication type D/A converter 10 will be described. As the multiplication type D/A converter 10, any type of general multiplication type D/A converter such as a weighted current addition type, an R-2R type, a MOS type, or a duty control type can be applied.

In general, the analog output voltage Vout of an m (bit) binary type multiplication type D/A converter can be obtained by the following equation for a set digital value n, where Vin is the voltage applied to the reference voltage terminal. It will be done.

Vout-Vin-n/2-...(3)
FIG. 3(a) shows an example of a weighted current addition type D/A converter 20. Further, an example of an R-2R type multiplication type D/A converter 30 is shown in FIG. 3(b). In the figure (b), 11 is a digital value register, and 12 is an analog switch. The multiplication type D/A converter 30 in the example of this figure has 3 (bi
t), so if the set digital value set in the digital value register 11 is n, the analog output voltage is calculated from the above equation (3) as follows: Vout-Vin-n/8 (4)
It is expressed as The analog switch in Figure 3(b) is
Multiplying D/A converter 4 replaced with S buffer 13
An example of 0 is shown in FIG. 3(C). This multiplication type D/A converter 40 basically operates in the same way as the above six examples, but since there is a limit to the operating voltage of the buffer 13 of the CMO3, the value of the voltage Vin applied to the base/$ voltage terminal is There are conditions.

When a multiplication type D/A converter as described above is used, the power variable constant becomes b -1/ n with respect to the set digital value n.

In addition, if a division type D/A converter, which is a type of duty control type and controls the duty to be 1 / n, is used as the multiplication type D/A converter, the output of this division type D/A converter is , is obtained by the following operation for the set digital value n.

Vout-Vin/n
-(5) In this case, the power variable constant is bn, and the human power and the set digital value set in the multiplication type D/A converter become proportional.

Division type D that controls the duty to be 1/n
An example of the /A converter 50 is shown in FIG. In the same figure, 14
is a digital comparator, 15 is an nbit counter,
16 is a negative logic AND gate, and 17 is an analog switch. In the division type D/A converter 50 of this example, when the value (n - 1) is set in the digital value register 11, the counter 15 repeats counting every n cycles of the clock, and only when the value of the counter 15 is zero. The output of the negative logic AND gate 16 becomes "1" of positive logic, and the on duty of the analog switch 17 becomes 1/n. Therefore, the average value of the output Vout follows equation (5).

[Effects of the Invention] As explained above, according to the first invention, since the anode current Ib of the magnetron is controlled based on the formula I bb - (a-Eb), the input of the magnetron Power P follows P-Eb.Ib-Eb-b.(a-Eb). For this reason, set the power variable constant to an appropriate value, and
The withstand voltage (of the magnetron, etc.) is approximately twice the average anode voltage of the magnetron used during normal operation.
If the limit anode-cathode voltage setting constant a is selected to the value of this limit voltage, the anode current Ib will have a linear characteristic with a negative slope with respect to the anode voltage Eb, and the input power P shows a maximum input power value (set input power) near the average anode voltage and becomes zero at the limit voltage, resulting in an upwardly convex quadratic curve characteristic. Therefore, even if the anode voltage Eb fluctuates around the average anode voltage during normal operation, the input power P is suppressed to a gentle fluctuation relative to the set human power, and stable operation is guaranteed. On the other hand, even if the anode voltage Eb tends to increase due to the occurrence of moding, etc., the anode current Ib decreases and the moding etc. subsides, and at the same time, the input power becomes zero at the limit voltage, and the magnetron etc. It has the advantage of being able to reliably prevent the destruction of.

Further, according to the second invention, the control having the same effect as the first invention can be performed by the control circuit itself using the voltage detection means, the current detection means, the multiplication type D/A converter, the addition means, and the control means. Therefore, there is an advantage that there is no need for a separate circuit for monitoring the limit voltage of the anode voltage, and the power control method for the magnetron power source can be implemented with an inexpensive circuit.

[Brief explanation of the drawing]

1 to 4 are diagrams for explaining an embodiment of the power control method of a magnetron power source according to the present invention, and FIG. 1 is a characteristic diagram showing the relationship between anode voltage and human power, etc., and FIG.
The figure is a block diagram showing an example of an inverter control circuit.
The figure is a circuit diagram showing an example of a D/A converter used in the inverter control circuit, and FIG. 4 is a circuit diagram showing another example of the D/A converter. 2: Inverter main circuit, 3: Magnetron, 4: Voltage detection means, 5: Current detection means, 6: Addition circuit (addition means), 7: Control circuit (control means), 10: Multiplying type D/A converter.

Claims (2)

[Claims] (1) When the voltage applied between the anode and cathode of the magnetron is Eb, the anode current Ib is expressed by the following formula Ib = b (a - Eb) where a: limit anode-cathode voltage setting constant b = power variable A power control method for a magnetron power source, characterized by controlling by a constant. (2) The voltage applied between the anode and cathode of the magnetron is detected by a voltage detection means, the anode current of the magnetron is detected by a current detection means, and the set digital value and the value of the voltage or current applied to the reference terminal are detected. A multiplication type D/A converter that multiplies the product and outputs the product as an analog value multiplies the set digital value by the anode current detection value detected by the current detection means, and outputs the product as an analog value.
The output value of the converter and the anode-cathode voltage detected by the voltage detection means are added by an addition means to which a predetermined reference voltage is set, and the anode current is controlled by the control means based on the output of the addition means. A power control method for a magnetron power source, characterized in that: