JPH03156881A - High-frequency heating device - Google Patents

Abstract

PURPOSE:To reduce the loss at the time of switching and improve reliability by switching the nonconductive period of a semiconductor switching element to separate lengths when a magnetron is started and when it is stabilized. CONSTITUTION:When positive voltage is applied across the base and emitter of a semiconductor switching element 5, the element 5 is turned on, and the magnetron 9 is driven by a magnetron driving circuit 8 serving as a half-wave double-voltage circuit. When negative voltage is applied across the base and emitter of the element 5, the element 5 is turned off, the electromagnetic energy stored in the exciting circuit of a transformer 3 is discharged into a snubber circuit 4 constituted of a diode 18, a capacitor 17 and a resistor 16, and the magnetic flux of the transformer 3 is reset. The off-period of the element 5 is set by optionally setting the reverse bias period outputted from a driving circuit 2. The off-period value of the element 5 is switched to separate nonconductive periods of different lengths by automatically judging the states when the magnetron 9 is started and when it is stabilized. The voltage between the collector and emitter of the element 5 is selected to the optimum low value, and the loss at the time of switching can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high frequency heating device, particularly to driving a magnetron.

[Conventional technology]

FIG. 7 is a control circuit diagram of a conventional high-frequency heating device disclosed in, for example, Japanese Unexamined Patent Publication No. 81-279094. In FIG. 1, (26) is a DC power supply, (B) is a smoothing capacitor, (3) ) Magnetron drive transformer, (27)
is a resonant capacitor connected in parallel to the transformer (3), (
5) is a semiconductor switching element connected in series to the transformer (3), (■ is a commutating diode connected in parallel to the semiconductor switching element (5), the transformer (3), the resonant capacitor (27), Semiconductor switching element (5)
Together with this, an inverter circuit is constructed. A high-voltage capacitor (2) is connected to the first winding on the secondary side of the transformer (3), and together with a high-voltage diode (21), constitutes a magnetron drive circuit (8) using a half-wave voltage doubler rectifier circuit. In addition, a transformer (
3) A diode (28) is installed in the second winding on the secondary side.

A capacitor (29) is connected to supply filament voltage to the magnetron (91).

A conventional high-frequency heating device is configured as described above.

The operation will be explained using the control timing waveform diagram shown in FIG.

When a positive voltage (30) shown in Fig. 8 (h) is applied between the base and emitter of the semiconductor switching element (5), the semiconductor switching element (5) turns on and the voltage shown in Fig. 8 (b) is applied to the transformer (3). A DC voltage (31) of Vdc shown in FIG. 8(e) is applied, and a current (32) shown in FIG. 8(e) flows through the transformer (3). At this time, the collector current IC and collector-emitter voltage Vee of the semiconductor switching element (5) are as shown in (33) and (34), respectively, shown in FIG. 8 (eL(d)).The base of the semiconductor switching element (5) During the period when a positive voltage (30) is applied between the emitters, that is, when the semiconductor switching element (5) is ONL, the transformation M
(DC voltage Vdc generated on the primary side of
) to generate a high voltage of several thousand V in the GL winding on the secondary side.

This high voltage is converted into the half-wave voltage doubler required to drive the magnetron (9) by a magnetron drive circuit (8), which may be a half-wave voltage doubler rectifier consisting of a high-voltage capacitor 12LD and a high-voltage diode (21). ) to drive it.

Next, when a negative voltage (35) shown in FIG. 8(a) is applied between the base and emitter of the semiconductor switching element (5),
The semiconductor switching element (5) is reverse biased and turned off.
do. When the semiconductor switching element (5) is turned off, its collector current 1c becomes zero, and the collector-emitter voltage Vce becomes 1 of the transformer (3) as shown in (36).
It jumps up as a resonant voltage of the next-side inductance and the resonant capacitor (27). This semiconductor switching element (
5) is OFF, the voltage on the primary side of the transformer (3) is (
31), the high-voltage diode (21) in the half-wave voltage doubler rectifier circuit on the secondary side of the transformer conducts in the direction of charging the high-voltage capacitor ω, and no current flows to the magnetron (9). Next, the point (2) at which the Vce of the semiconductor switching element (5) becomes zero is detected, and a positive voltage of Vbeζ is applied again to turn the semiconductor switching element (5) into the ON state.

The conventional control method that drives the magnetron by repeating the above is widely known as the voltage resonance method, which turns on the semiconductor switching element (5) when Vce becomes zero, so there is little switching loss when it is turned on. There is.

Figure 9 is a high-frequency output correlation diagram, and in order to increase the high-frequency output, it is sufficient to increase the ON time of the semiconductor switching element (5), that is, the period during which current flows through the magnetron (9), as shown in Figure 9 (37). It becomes like this. However, at this time, a voltage resonant circuit consisting of the transformer (3) and the resonant capacitor (rr) is used, and the collector-emitter voltage of the semiconductor switching element (5) becomes zero and the point is fixed. This is because the OFF time of the semiconductor switching element (5) cannot be arbitrarily selected.

The relationship between switching frequency and high frequency output is shown in Figure 10 (
It is inversely proportional as shown in 38).

[Problem to be solved by the invention]

As mentioned above, in conventional high-frequency heating devices, the OFF time of the switching element is determined by the resonance conditions.

It is not possible to arbitrarily adjust the OFF time, and it is troublesome that fine adjustments cannot be made. In addition, when trying to lower the high frequency output, the switching frequency increases, and semiconductor switching elements, [e,) lances, and ferrite cores that are more suitable for high frequencies are required.

The problem was that it increased costs, and at the same time, the circuit was not suitable for obtaining high-frequency output over a wide range.

This invention was made to solve the above problems, and aims to reduce loss during switching and obtain a reliable high-frequency heating device.

[Top means to solve problems]

The high-frequency heating device according to the present invention rectifies and
A rectifier/smoothing circuit that smoothes and creates DC power.

A transformer connected to this rectifying/smoothing circuit, a snapper circuit connected in parallel to this transformer, a semiconductor switching element connected in series to the transformer, and a drive circuit that drives this semiconductor switching element.

a magnetron drive circuit connected to the secondary side of the transformer; a magnetron driven by the magnetron drive circuit; It is set to 1, and automatically switches to 1/2.

[Made by Tears]

The high-frequency heating device according to the present invention arbitrarily adjusts the output of the drive circuit to adjust the ON time of the semiconductor switching element and the O
By freely controlling the FF time, setting the OFF time to different lengths for magnetron startup and stabilization, and automatically switching, the semiconductor switching element can be made conductive when Vce is low. Loss during switching can be reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the high frequency heating device according to the present invention.
FIG.

In the figure, (1) is a commercial power supply, and (2) is a rectifier/smoothing circuit, which is connected through a fuse α0) and a switch (11).

It consists of a rectifying element (shame, smoothing choke coil 03) and a smoothing capacitor (2). (One is the limiting resistor connected to the rectifier/smoothing circuit (2), (3) is the magnetron drive transformer M, (41 is the snapper circuit connected to the transformer (3).

Consists of a capacitor (1?), a resistor (IQ), and a diode (8). (5) is a semiconductor switching element connected in series to the transformer (3), and (1!l) is a semiconductor switching element connected in parallel to the semiconductor switching element (5). is a connected free-wheeling diode,
Transformer (3).

An inverter circuit (6) is configured together with the ZNAPA circuit (4) and the semiconductor switching element (5). A drive circuit (7) is connected to the base of the semiconductor switching element (5).

A high-voltage capacitor (to) is connected to the first winding on the secondary side of the transformer (3), and together with a high-voltage diode (21) constitutes a magnetron drive circuit (8) using a half-wave voltage doubler drive circuit. A high voltage is supplied to the magnetron (9) through an off-diode (22). Further, the filament of the magnetron (9) is similarly connected to the second winding on the secondary side of the transformer (3), and a filament voltage is supplied to the magnetron (9). (23) and (24) are magnetron anode current detection resistors, (23) serves as an output control detection and overcurrent detection resistor, and (24) serves as a magnetron peak current limiting resistor. Detection resistor (23
), (24) are input to the detection circuit (25), the output of the detection circuit (25) is input to the drive circuit (7), and the output of the drive circuit (7) drives the semiconductor switching element (5). drive.

Next, the operation of the above embodiment will be explained using the control timing waveform diagram shown in FIG.

When a positive voltage (39) shown in Fig. 2(a) is applied between the base and emitter of the semiconductor switching element (5), the semiconductor switching element (5) turns ONI, and the transformer (3) turns ONI as shown in Fig. 2(a). A DC voltage (4o) of Vdc shown in b) is applied.

A current (41) shown in FIG. 2(e) flows through the transformer (3).

At this time, the collector current Ic and collector-emitter voltage Vce of the semiconductor switching element (5) are shown in FIGS. 2(e) and (d), respectively (42) and (43).
become that way.

During the period when a positive voltage (39) is applied between the base and emitter of this semiconductor switching element, that is, during the period when the semiconductor switching element (5) is ON, the DC voltage Vdc generated on the primary side of the transformer (3) is transformed. Boost the pressure in the device (3) to 2
A high voltage of several thousand KV is generated in the first winding on the next side. This high voltage is connected to a high voltage capacitor (to) and a high voltage diode (2).
) magnetron drive port, which is a half-wave voltage doubler rectifier circuit consisting of! '2i (8) converts the voltage into a half-wave doubler voltage necessary to drive the magnetron (9).
A current is applied to drive the magnetron (9).

Next, as shown in FIG.
FF. When the semiconductor switching element (5) is turned off, its collector B tYE r c becomes zero, and the collector-emitter voltage Vce is caused by the electromagnetic energy stored in the excitation circuit of the transformer (3) being connected in parallel with the transformer-next winding. Connected diode (■, capacitor (■.

The magnetic flux of the transformer (3) is reset by discharging into the snapper circuit (4) consisting of a resistor (l).At this time, the magnetic flux of the transformer (3)
A reset voltage appears in the secondary winding of the transformer (3), but a high voltage diode (21) is applied in the direction that charges the high voltage capacitor (to) of the magnetron drive circuit (8), which is a half-wave voltage doubler rectifier circuit. conducts and no current flows through the magnetron (9). Next, the V of the semiconductor switching element (5)
At an arbitrary point 0 of ce, a positive voltage (39) is again applied to Vbe to turn on the semiconductor switching element (5). By repeating the above operations, it is possible to drive the magnetron and generate high frequency waves from the high frequency heating device to heat the food.

FIG. 3 is a high-frequency output correlation diagram. As shown in (44), the ON time (to
As n) becomes longer, the high frequency output increases.

With 0FFvf@ of the semiconductor switching element (5), the time during which the reverse bias voltage of Vbe output from the drive circuit (7) is applied can be set arbitrarily, so the relationship between the high frequency output and the switching frequency is shown in Figure 4 (45). Proportional &
2 can be freely set as inversely proportional to constant C.

Figure 5 shows the drive circuit (7) of the semiconductor switching element (5).
) is shown. In Figure 5, two oscillation circuits (7
In 1), the oscillation frequency is determined and the OFF time-window circuit (
72) fixes the OFF time to an arbitrary value. This O
An output with a fixed FF time is output to the drive circuit [73] to drive the semiconductor switching element (5).

Figure 6 shows the flipter-emitter voltage Vc when the semiconductor switching element (5) is conductive when the OFF time is changed.
e, and in this example, there are the relationships shown in FIGS. 6(a) and 6(b), respectively.

This is because the impedance of the magnetron (9) when it is not oscillating is almost infinite, and the impedance when it is oscillating is low resistance, so the magnetron anode voltage ebm.

During non-oscillation, the voltage is high as shown in Fig. 6(a) (49), and during one oscillation, it is rectified by half-wave voltage doubler and becomes low as shown in Fig. 6(b) (50). The collector-emitter voltage Vce waveform also has different waveforms during startup and stability, as shown in FIG. 6(a) (51) and FIG. 6(b) (52).

In other words, it is Jin at startup. The shorter ff is, the lower the VCe is, and the more stable it is. The longer jf is, the lower Vce is.

That is, by changing the tolf time at startup (when the magnetron is not oscillating) and when it is stable (when the magnetron is oscillating), the V when the semiconductor switching element (5) is conductive is varied.
It is possible to select an optimal low value for ee.

Loss during conduction of the semiconductor switching element (5) can be reduced.

Next, an embodiment of a circuit for switching the OFF time of the semiconductor switching element (5) during startup and stabilization will be described using FIG. 5. At startup, the magnetron (9) is in a non-oscillating state and no voltage drop occurs in the output control detection resistor (23) because the magnetron current (Img) does not flow.

Therefore the comparator (54) in the detection circuit (25)
The output of is in the HIGH state. After a while, the magnetron (9) starts oscillating, and the magnetron current rm
g flows, and a voltage drop occurs across the output control detection resistor (23). Therefore, if the potential on the input side of the humpator (54) in the detection circuit (25) is set to a certain value, the magnetron voltage i! When iff, Img flows, the output of the comparator (54) can be set to r=oW state. The output of this comparator (54) is connected to the drive circuit (7).
OFF time of - by inputting into the window circuit (72).

Comparator output HIGH, LOW status,
The OFF time can be set according to the situation.

In other words, the startup and stable states of the high-frequency heating device are automatically determined, and the semiconductor switching element (5) is turned off.
You can change the time.

〔Effect of the invention〕

As described above, according to the present invention, the value of the OFF time of the semiconductor switching element of the high-frequency heating device is set to different lengths for startup and stabilization and is automatically switched, so that Vce of the semiconductor switching element is increased. Since conduction can be made at a low temperature, loss during switching can be reduced and reliability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a control circuit diagram of an embodiment of the high-frequency heating device according to the present invention, FIG. 2 is a control timing waveform diagram of the embodiment shown in FIG. 1, and FIGS. A high-frequency output correlation diagram of the embodiment, FIG. 5 is a configuration diagram showing details of the main parts of the embodiment shown in FIG. 1, and FIG. 6 explains the operation of the semiconductor switching element of the embodiment shown in FIG. 1. Waveform diagram for FIG. 7 is a control circuit diagram of a conventional high-frequency heating device, FIG. 8 is a control timing waveform diagram thereof, and FIGS. 9 and 10 are high-frequency output correlation diagrams thereof. In the figure, (1) is a commercial power supply, (2) is a rectifier/smoothing circuit, (3) is a transformer, (4) is a snapper circuit, (5) is a semiconductor switching element, (7) is a drive circuit, (81) is a 1 is a magnetron drive circuit, and (9) is a magnetron. Note that the same reference numerals in the two figures indicate the same or corresponding parts.

Claims (1)

[Claims] A rectifier/smoothing circuit that rectifies and smoothes commercial power to create DC power, a transformer connected to this rectifier/smoothing circuit, a snapper circuit connected in parallel to this transformer, and a snare circuit connected in series to the transformer. A semiconductor switching element, a drive circuit for driving the semiconductor switching element, a magnetron drive circuit connected to the secondary side of the transformer, and a magnetron driven by the magnetron drive circuit, and a non-conducting period of the semiconductor switching element. A high-frequency heating device characterized in that the magnetron is set to different lengths when the magnetron is activated and when it is stable, and the lengths are automatically switched.