JPH02257588A - Microwave oven having rush current suppression function - Google Patents

Abstract

PURPOSE:To suppress the rush current of a high-tension transformer by measuring a delay time elapsed from the time when a microwave generation command is outputted to the time when current is applied to a switching means, thus operating the switching means prior to the time when a rush current is minimized, by a delay time. CONSTITUTION:For driving a turn table motor 12, a H-level signal is outputted from an output port A at the time of Tk. This causes the coil 103 of a relay to be applied with current so that relay contacts 101, 102 are made conductive so as to feed power from a power source 2 to the motor 12. At the time of Tm after a elapse of Ti, based on the last transition time Tl of a power source synchronizing signal, since the motor is certainly turned on, the H-level signal is outputted from an output port B, wherein T1=T2- T, T2 being 3/4 period of the power source synchronizing signal. Thus, the contacts 141, 142 are made conductive at the time Tm when the rush current is made minimum for starting to flow current at a high tension transformer 18. Accordingly, the high tension transformer is less liable to be applied with a large current at the time of starting of current-applying.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a microwave oven, and more particularly to a microwave oven having a function of suppressing inrush current when a high voltage transformer feeding power to a magnetron is turned on.

[Prior Art] FIG. 4 is a circuit diagram showing the electrical configuration of a conventional microwave oven. In Figure 4, a commercial AC power supply (hereinafter referred to as ACfI
Power from the power supply transformer 4 is supplied to the primary winding 41 of the power transformer 4 for the control circuit. The AC power output by the secondary winding 42 of the control circuit power transformer 4 is rectified by a full-wave rectifier circuit 6 made of diodes, smoothed by a capacitor C1, and then supplied to a constant voltage circuit 8.

Let V be the DC voltage supplied to the constant voltage circuit 8.

This DC voltage V is used as a driving power source for a relay, which will be explained later. DC voltage V stabilized by constant voltage circuit 8
oo (negative potential) is obtained, which is the microprocessor 1
is supplied to the power terminal of the Full wave rectifier circuit 6. The ground terminals of capacitor CI, constant voltage circuit 8, and microprocessor 1 are connected to earth.

The collector of the transistor TRI is - absolutely DC voltage V
It is connected to the other end of the resistor R1 to which DD is applied, and its emitter is grounded. Further, an AC voltage output from the secondary winding 42 of the control circuit power transformer 4 is applied to the base of the transistor TRI via a resistor R2. Therefore, the collector-emitter of the transistor TR1 is turned on/off in synchronization with the AC power supply. As a result, a power synchronization signal is taken out from node N1 and applied to microprocessor 1.

AC power source 2 is connected to turntable motor 12 via contacts 101, 102 of relay 10. relay 1
One end of the No. 0 coil 103 is grounded, and the other end is connected to the collector of the transistor TR2 of the relay drive circuit 11. A DC voltage V is applied to the emitter of the transistor TR2. In this state, when a signal of "H level" is applied from the boat A of the microprocessor 1 to the base of the transistor TR2 via the resistor R3, conduction occurs between the collector and emitter of the transistor TR2, and the coil 1
Current flows through 03. Therefore, electrical conduction occurs between the contacts 101 and 102, and power is supplied to the turntable motor 12. The turntable motor 12 has a function of rotating a turntable (not shown) provided in the microwave oven.

In addition, the AC power source 2 is connected to the contacts 101 and 102 of the relay 10.
It is also connected to a high voltage transformer 18 that supplies power to the magnetron 16 via contacts 141 and 142 of the relay 14 . It is now assumed that the contacts 101 and 102 of the relay 10 are closed.

One end of the coil 143 of the relay 14 is grounded, and the other end is connected to the collector of the transistor TR3 of the relay drive circuit 13. A DC voltage V is applied to the emitter of the transistor TR3. In this state, when an "H" level signal is applied from the boat B of the microprocessor 1 to the base of the transistor TR3 via the resistor R4, conduction occurs between the collector and emitter of the transistor TR3, and a current flows through the coil 143. For this reason, contact 141
．． 142 is electrically connected, power is supplied to the high voltage transformer 18, and microwaves are output from the magnetron 16.

FIG. 5 is a waveform diagram of the circuit shown in FIG.
Figure <a> shows the waveform of the AC power supply, Figure 5(b) shows the waveform of the power synchronization signal, Figure 5(C) shows the port B output signal of the microprocessor 1, and Figure 5(d) shows the waveform of the power synchronization signal. ) indicates a state in which conduction is interrupted between the contacts 141 and 142 of the relay 14.

The cycle of AC power is 20 if 50H2 is used.
m seconds, and if 60Hz is used, 16.7m
Seconds. The power supply synchronization signal is synchronized with the waveform of the AC power supply. Therefore, the period of the power supply synchronization signal is the same as that of the AC power supply.

Next, with reference to FIGS. 4 and 5, a method for suppressing the rush current of a high voltage transformer of a magnetron employed in a conventional microwave oven will be described.

In order to minimize the inrush current of the high voltage transformer 18, if there is no phase shift due to the coil load of the high voltage transformer 18,
The relay contacts 141 and 142 may be electrically connected at the time when the AC power becomes OV, for example, at time To. but,
Since the high-voltage transformer 18 is loaded with a coil, the phase is 90" out of phase with the AC power waveform. Therefore, as shown in FIG. The inrush current will be minimized if the relay 14 is connected to the port B of the microprocessor 1.
After receiving an “H” level signal from contact 141,
There is a predetermined delay time ΔT until conduction occurs between the terminals 142 and 142. Therefore, the point in time when the output signal of boat B of microprocessor 1 is changed from "L" level to "H" level is
If the time point Tb is set ΔT before the time point Ta, the rush current of the high voltage transformer 18 will be minimized. For this reason, in a conventional microwave oven, T1 obtained by measuring general-purpose parts and using the following formula (1) is stored in advance in a memory (not shown), and a time T1 is reached after a time T1 from the time Tc when the power synchronization signal falls.
b, the output signal from boat B was set to the "H" level.

Tl-T2-ΔT...(1) Here, T2 is 3/4 period of the power synchronization signal.

[Problems to be Solved by the Invention] However, the input voltage of the AC power R2 fluctuates, the low voltage transformer 4 and power supply circuit components vary, and the relay drive circuit 13 and relay 14 vary. For this reason, it was not always possible to suppress the rush current at the start of energization.

For this reason, in the conventional microwave oven, a large current flows through the high voltage transformer 18 when power is started, and the magnetic flux attracts iron plates such as the cabinet, causing abnormal noise. Also,
A large current flows through relays and other components, placing a heavy burden on these components.

Therefore, an object of the present invention is to provide a microwave oven having an inrush current suppressing function capable of suppressing inrush current of a high voltage transformer of a magnetron.

[Means for Solving the Problems] The present invention provides a power supply, a high voltage transformer that supplies power to a magnetron that generates microwaves, an output means that outputs a command signal instructing microwave generation, and a command signal from the output means. The microwave oven is equipped with a switch means that conducts in response to the power source, thereby enabling power to be supplied from the power source to the high-voltage transformer, and when power is not supplied from the power source, the output means outputs a command signal. measuring means for measuring the delay time from the moment when the switching means is turned on until the switching means becomes conductive; and control means for controlling the switch means to operate the switch means a delay time before the point in time.

[Operation] In this invention, before power is supplied to the switch means,
The delay time from when a microwave generation command is issued to when the switch means becomes conductive is always measured, and the switch means is activated a delay time before the time when the rush current becomes minimum.

Embodiment of the Invention FIG. 2 is a circuit diagram showing the electrical configuration of a microwave oven according to an embodiment of the invention. The circuit shown in FIG. 2 differs from the conventional example shown in FIG. 4 in that a capacitor C2 is inserted between the constant voltage circuit 8 and the power supply terminal of the microprocessor 1 to stabilize the power supply. The relay 14 is a two-contact relay, and its added contact is connected to the port C of the microprocessor 1.The rest is the same as the conventional example, so the same parts have the same reference numerals. will be added and the explanation will be omitted.

The relay 14 has a contact 14 in addition to the contacts 141 and 142.
Contacts 145 and 146 are provided which open and close synchronously with contacts 1 and 142. The contact 145 is grounded, and the contact 146 is connected to the input port C of the microprocessor 1 and to the stabilized power supply Voo (negative potential) via a resistor R5.

FIG. 3 is a waveform diagram of the circuit shown in FIG.
Figure (a) shows the waveform of the AC power supply, Figure 3 (b) shows the waveform of the power synchronization signal, Figure 3 (c) shows the waveform of the output port B, and Figure 3 (d) shows the waveform of the input port. The waveform of boat C is shown, and FIG. 3(e) shows the waveform of output boat A.

FIG. 1 is a flow diagram for explaining the operation of an embodiment of the present invention. Next, referring to Figures 1 to 3,
The operation of one embodiment of this invention will be explained.

Referring to FIG. 3, at time point Ti corresponding to the fall of the power synchronization signal, an "H" level signal is output from output port B of microprocessor 1, and an internal timer (not shown) of microprocessor 1 is output. Start. At this time, the output port A outputs an "L" level signal. For this reason, the coil 103
No current flows through contacts 101. of relay 10.
102 is cut off.

Current flows through the coil 143 of the relay 14 due to the "H2 level signal from port B, and conduction occurs between relay contacts 145 and 146. Until relay contacts 145 and 146 close, 'L' is applied to input port C.

A level signal is given. Contact 145 of relay 14
．． At the time Tj when 146 is closed, that is, when the microprocessor 10 man-powered boat C becomes H" level, the timer is stopped. Since the relay contacts 141 and 142 open and close at the same time as the relay contacts 145 and 146, the relay contacts 141° The delay time ΔT of 142 is the timer value Tj-
It is given by Ti. Subsequently, the signal output from port B is set to "L" level. As a result, relay contact 14
1. Question 142 and relay contacts 145 and 146 are cut off again.

Next, in order to drive the turntable motor 12, an "H° level signal is output from the output boat A at time Tk. As a result, current flows through the coil 103 of the relay 10, and conduction occurs between the relay contacts 101 and 102. Power is supplied from the power source 2 to the turntable motor 12. After the turntable motor 12 is turned on reliably, a period of time Tl starts from the falling time Tu of the power synchronization signal.
At a later time point Tm, the output port B outputs an "H" level signal. Here, TI-T2-ΔT, and T2 is 3/4 cycle of the power synchronization signal. As a result of the above, conduction occurs between the contacts 141 and 142 of the relay 14 at the time point Tm when the inrush current at the start of energization of the high voltage transformer 18 is at its minimum. Therefore, a large current does not flow through the high voltage transformer 18 at the start of energization, and no abnormal noise is generated.

[Effects of the Invention] As described above, according to the present invention, the delay time from the time when a microwave generation command is given before power is supplied to the switch means until the switch means becomes conductive is fixed.
Since the switch means is operated a delay time before the point when the inrush current is at its minimum, it is possible to prevent a large current from flowing into the high voltage transformer and to prevent abnormal noise caused by magnetic flux. . Therefore, a large burden is not placed on components such as relays. Further, since components such as cushions for preventing abnormal noises and current control resistors for preventing large currents are not required, the microwave oven can be provided at low cost.

[Brief explanation of drawings]

FIG. 1 is a flow diagram for explaining the operation of an embodiment of the present invention. FIG. 2 is a circuit diagram showing the electrical configuration of a microwave oven according to an embodiment of the present invention. FIG. 3 is a waveform diagram of the circuit shown in FIG. 2. FIG. 4 is a circuit diagram showing the electrical configuration of a conventional microwave oven. FIG. 5 is a waveform diagram of the circuit shown in FIG. 4. In the figure, 1 is a microprocessor, 2 is a power supply, 10
is a relay, 14 is a 2-contact relay, 16 is a magnetron,
18 is a high voltage transformer, 101, 102. 141, 142
, 145 and 146 indicate relay contacts. Figure 1

Claims (1)

[Scope of Claims] A power source, a high-voltage transformer that supplies power to a magnetron that generates microwaves, an output means that outputs a command signal that commands microwave generation, and conduction in response to the command signal from the output means. and switch means for enabling power supply from the power source to the high voltage transformer, wherein the command signal is output by the output means when power is not being supplied from the power source. measuring means for measuring a delay time from a point in time until the switching means becomes conductive; and a measuring means for making the switching means conductive at a time when the inrush current of the high voltage transformer is at a minimum when power is being supplied from the power supply. , and control means for controlling the switch means to be activated by the delay time from that point in time, the microwave oven having an inrush current suppressing function.