JPH02278692A - Microwave oven - Google Patents

Abstract

PURPOSE:To enhance the utilizing efficiency of electric power in a low voltage dc power source and achieve miniaturization and light-weightness therefore by providing a reactor connected in series to the low voltage dc power source and a push-pull inverter circuit for intermittently applying the electric power of the low voltage dc power source to the reactor. CONSTITUTION:A reactor 3 for generating a high pressure ac voltage is connected to a low voltage dc power source 2. The electric power of the low voltage dc power source 2 is intermittently applied to the reactor 3. There is provided a push-pull inverter circuit 4 for generating a voltage in the reactor 3. Consequently, in an electronic range 1, the voltage is generated in the reactor 3 so as to work together with the power source voltage, thus enhancing the utilizing efficiency of the electric power in the low voltage dc power source 2. Moreover, the voltage generated in the reactor 3 is added to the output voltage of the low voltage dc power source 2 so that the number of winding of a booster transformer 5 can be reduced. Therefore, miniaturization and light-weightness of the microwave oven can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a microwave oven, and more particularly to a microwave oven driven by a low-voltage DC power source.

[Prior art]

FIG. 7 shows a conventional microwave oven driven by commercial power.

In this microwave oven 51, a commercial power source 52 is connected to a rectifier circuit 53.
After being rectified into a DC voltage, the voltage is exchanged by a -stone resonance inverter circuit 54 into a high-frequency AC voltage having the DC voltage as a peak voltage.

Then, this high frequency AC voltage is boosted by a step-up transformer 55, and the boosted AC voltage is further transferred to a voltage doubler rectifier circuit 55.
6, the voltage is doubled, rectified, and applied to the magnetron 57.

Conventionally, when this microwave oven 51 is driven using a low voltage DC power source such as 12V or 24V of an automobile battery, as shown in FIG.
is connected to the commercial power supply 52 by the DC/AC inverter 59.
was converted into AClooV, and this AClooV was given to the microwave oven 51.

[Problem to be solved by the invention]

That is, in the conventional microwave oven 51, when using the low voltage DC power supply 58, the low voltage DC power supply 58 is converted from DC to AC (AC) by the DC/AC inverter 59 as described above.
looV) and further rectifier circuit 5 of microwave oven 51.
After the alternating current is returned to direct current in step 3, a high-frequency alternating current voltage of a predetermined peak voltage is generated by the -stone resonance type inverter 54.

For this reason, the power utilization efficiency is extremely low, and automobile batteries, etc., which have limited capacity, are wasted unnecessarily.

Furthermore, the conventional microwave oven 51 is too large to be loaded into a narrow vehicle or the like, and is not convenient to carry.

Therefore, it is an object of the present invention to provide a microwave oven that uses a low-voltage DC power source, improves the power utilization efficiency of the low-voltage DC power source, and can be made smaller and lighter.

[Means to solve the problem]

In order to achieve the above object, the present invention generates a high-voltage AC voltage using a low-voltage DC power supply, steps up the high-voltage AC voltage with a step-up transformer, rectifies the stepped-up AC voltage, and applies it to a magnetron. An electronic microwave oven comprising: a reactor connected in series with the low-voltage DC power supply; and a push-pull inverter circuit that intermittently applies power from the low-voltage DC power supply to the reactor. It is configured as a range.

[Effect]

Therefore, if the microwave oven configured as described above is used, a reactor for generating the high-voltage AC voltage is connected to the low-voltage DC power supply, and the push-pull inverter circuit connects the reactor to the low-voltage DC power supply. is applied intermittently to generate a voltage across the reactor.

This voltage is synergized with the low-voltage DC power supply and further boosted by the step-up transformer, and the boosted AC voltage is rectified and applied to a magnetron to heat food, for example.

As mentioned above, in this microwave oven, the voltage generated in the reactor is multiplied with the low voltage DC power supply, so
The low voltage DC power source can be used directly without converting the low voltage DC power source to AC power such as AClooV as in the conventional case.

Therefore, the power utilization efficiency of the low-voltage DC power supply can be significantly improved compared to the prior art.

Further, as described above, since the reactor is connected to the low voltage DC power supply, the voltage generated in the reactor is added to the low voltage DC power supply voltage and is applied to the step-up transformer.

Therefore, the number of turns of the step-up transformer can be reduced,
This microwave oven can be made smaller and lighter.

〔Example〕

Hereinafter, embodiments embodying the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.

It should be noted that the following examples are examples embodying the present invention, and are not intended to limit the technical scope of the present invention.

FIG. 1 is a block diagram of a microwave oven according to an embodiment of the present invention, FIG. 2 is a circuit diagram of the same microwave oven, FIG. 3 is a current-voltage characteristic diagram of the magnetron of the same microwave oven, and FIG. A block diagram of the control circuit of the microwave oven, and FIGS. 5 and 6 are time charts of the control circuit.

In FIG. 1, a microwave oven 1 according to an embodiment of the present invention is shown.
is driven using a low voltage DC power source 2 such as 12V24V of an automobile battery, for example.

In this microwave oven 1, a reactor 3 for generating a high voltage AC voltage is connected to the low voltage DC power supply 2.

Furthermore, a push-pull inverter circuit 4 is provided that intermittently applies power from the low voltage DC power supply 2 to the reactor 3 to generate a voltage in the reactor 3.

The voltage generated in the reactor 3 is the low voltage DC power supply 2
The voltage is added to the output voltage of the voltage converter 5, is boosted by a step-up transformer 5, is doubled and rectified by a voltage doubler rectifier circuit 6, and is applied to a magnetron 7 to heat food, for example.

As mentioned above, in this microwave oven 1, a voltage is generated in the reactor 3 connected to the low voltage DC power supply 2, and is multiplied with the power supply voltage, so that the power usage efficiency of the low voltage DC power supply 2 can be improved compared to the conventional one. can be significantly increased compared to .

Furthermore, since the voltage generated in the reactor 3 is added to the output voltage of the low-voltage DC power supply 2, the number of turns of the step-up transformer 5 can be reduced, and as a result, the microwave oven can be made smaller and lighter. can.

Next, the circuit operation of this microwave oven 1 will be explained with reference to the circuit diagram shown in FIG.

In this microwave oven 1, a push-pull inverter circuit 4
When the switching elements TrI and Tr2 are turned on simultaneously, the primary winding of the step-up transformer 5 is short-circuited, and the electrical energy of the low-voltage DC power supply 2 is supplied to the reactor 3 connected to the low-voltage DC power supply 2. can be stored.

Thereafter, when the switching element Tr is turned off, the electrical energy stored in the reactor 3 charges the capacitor C1 of the voltage doubler rectifier circuit 6 via the step-up transformer 5.

Therefore, when the switching element TrI is turned on again to store energy in the reactor 3, and then the switching element Tr2 is similarly turned off, the capacitor C2 is charged by the energy stored in the reactor 3, and the switching element Tr1. Tr switching is repeated.

That is, the voltage generated in the reactor 3 due to the accumulation and release of electrical energy by the reactor 3 is added to the output voltage of the low voltage DC power supply 2 and is applied to the step-up transformer 5.
The voltage is boosted by the voltage doubler rectifier circuit 6, and the voltage is doubled and rectified by the voltage doubler rectifier circuit 6, and then applied to the magnetron 7.

Then, the magnetron 7 outputs high frequency power, and food, etc. in a heating chamber (not shown) is heated by this high frequency power.

The current-voltage characteristics of the magnetron 7 are nonlinear load characteristics having a cutoff voltage of 3.5 to 4.0 kV, as shown in FIG.

Therefore, the power supply to the magnetron 7 is controlled by keeping the peak value of the voltage applied to the magnetron constant and controlling the magnetron current.

Next, the switching elements Try and Tr2 of the bush-pull inverter circuit 4 are turned on.

The control circuit 8 that controls the off operation will be explained with reference to FIGS. 4, 5, and 6.

The output signal of the oscillation circuit 9 of this control circuit 8 is shown in FIG.
, the applied voltage applied to the magnetron 7 is turned on,
Give an off period in advance. This output signal is “high”
During the period, an applied voltage is applied to the magnetron 7, and during the "low" period, no voltage is applied to the magnetron 7.

The on/off period of the output voltage of the oscillation circuit 9 is determined by the reactor current detection circuit 3 shown in FIG. 2 which detects the current of the reactor 3. Based on the detected reactor current value, the correction is made by the operation of the comparator circuit 10, etc., which will be described below.

In other words, the difference between the preset reactor current reference value and the reactor current detection value is the error amplification amplifier 1.
1, and this detection output shown by the broken line in FIG. The on/off period of the output voltage of the oscillation circuit 9 is modified as shown in FIG.

The oscillation circuit 12 generates a basic clock signal for controlling the on/off operation of the switching element TrlTr2, and its output signal is shown in FIG. 5fc).

Based on this basic clock signal, the above-mentioned comparison circuit 1
The output signal of 0 is waveform-shaped by the flip-flop circuit 13 as shown in FIG.

Based on the waveform-shaped output signal of the flip-flop circuit 13 and the basic clock signal, the AND gate 14 controls the switching elements Tr1. A clock signal shown in FIG. 5(e) for turning Tr2 on and off is output.

FIG. 6(a) shows the clock signal △ shown in FIG.
This is an enlarged view of the period T.

Then, the output signal (
Based on FIG. 6(b)), the triangular wave generation circuit 16 operates to generate the triangular wave A shown in FIG. 6(d), and the comparator circuit 1
Give to 7.

The comparator circuit 17 then compares the triangular wave A with a preset switching element ON time setting value shown by the broken line dl in FIG. 6 (fl), and outputs a control signal for the switching element Trl as shown in FIG. do.

Similarly, the triangular wave B shown in FIG. 6(e) is generated by the triangular wave generating circuit 19 based on the output signal (FIG. 6(C)) of the negative edge one-shot circuit 18 that detects the negative edge of the clock signal. generated and compared circuit 2
given to 0.

Similarly, the comparison circuit 20 outputs a control signal for the switching element Tr2 shown in FIG. 6 (gl).

The control signal of the switching element TrI and Tr
2 control signals, the switching elements TrI and Tr2
are controlled on and off, and when the "high" periods of these control signals overlap, TrTr2 is simultaneously turned on and energy is stored in the reactor 3. This Trl, T
The period during which r2 is simultaneously on is adjusted by adjusting the switching element on time setting value, and thereby the voltage value generated in the reactor 3 is adjusted.

As described above, the magnetron applied voltage is set to a constant value by adjusting the switching element on-time setting value, and the "high" period of the output signal of the oscillation circuit 9 and the reactor current reference value are adjusted. The magnetron current can be set to a desired value.

Therefore, the output of the magnetron 7 can be stably and variably controlled.

Note that the combination of the step-up transformer 5 and the voltage doubler rectifier circuit 6 of the microwave oven 1 described above is, for example, a step-up transformer with a larger winding ratio instead of the step-up transformer 5 and a combination of the step-up transformer 5 and the voltage doubler rectifier circuit 6. It may be combined with a normal rectifier circuit that does not double the voltage.

Similarly, a plurality of step-up transformers 5 may be provided and combined with a normal rectifier circuit in which the voltage doubler circuit is omitted.

Furthermore, although the above-mentioned voltage doubler rectifier circuit 6 has a double magnification and full-wave rectification as an example, other magnifications or half-wave rectification may be used.

〔Effect of the invention〕

According to the present invention, it is possible to provide a microwave oven in which the power utilization efficiency of a low-voltage DC power source is greatly improved.

Further, since the voltage generated in the reactor is applied to the low voltage DC power supply, the number of turns of the step-up transformer can be reduced, and as a result, the microwave oven can be made smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a microwave oven according to an embodiment of the present invention, FIG. 2 is a circuit diagram of the same microwave oven, FIG. 3 is a current-voltage characteristic diagram of the magnetron of the same microwave oven, and FIG. A block diagram of the control circuit of the microwave oven, Figures 5 and 6 are time charts of the control circuit, Figure 7 is a block diagram of an example of a conventional microwave oven, and Figure 8 is a low voltage DC FIG. 3 is a block diagram of an example of a case where the device is driven by a power source. [Explanation of symbols] l...Microwave oven 2...Low voltage DC power supply 3...Reactor 4...Push-pull inverter circuit 5...Step-up transformer 6...Voltage doubler rectifier circuit 7... magnetron.

Claims (1)

[Claims] 1. Generate high-voltage AC voltage using a low-voltage DC power supply,
A microwave oven in which the high-voltage AC voltage is boosted by a step-up transformer, the boosted AC voltage is rectified and applied to a magnetron, and the reactor is connected in series to the low-voltage DC power supply; A microwave oven comprising a push-pull inverter circuit that intermittently applies power from a power source.