KR20020019503A - Safety Circuit Of a DC Microwave Oven - Google Patents

Abstract

PURPOSE: A DC(Direct Current) safety circuit of a microwave oven is provided to prevent the damage of circuit devices by detecting the monitoring operation of a monitor switch and the generation of overcurrent. CONSTITUTION: First switching contacts(N11,N21) of first and second monitor switches(MSW11,MSW22) are connected to a plus(+) terminal of a DC current source via a fuse(FUSE1) and second switching contacts(N12,N22) thereof are connected to first and second transistors(50,51). Base terminals of the first and second transistors(50,51) are connected to first and second pulse output terminals(OUT1,OUT2) of a pulse driving circuit(VFC2). Collector terminals of the first and second transistors(50,51) are connected to the second switching contacts(N12,N22) of the first and second monitor switches(MSW11,MSW22).

Description

Safety Circuit of a DC Microwave Oven

The present invention relates to a microwave oven, and more particularly, to a safety circuit of a microwave oven for satisfying the safety of the microwave oven for driving the magnetron by converting the DC power to the alternating current.

As is well known, a general microwave oven is applied with a commercial AC power source of 110 ~ 230V to form a high pressure, and then drive the magnetron by the high pressure to generate a microwave, so that the desired cooking function can be implemented Microwave ovens are commonly employed.

However, since the conventional AC microwave oven is designed to be driven using only commercial AC power, there is a problem that it cannot be used in various transportation means such as vehicles, ships, aircrafts, etc., where AC power is difficult to supply. Is generated.

In order to solve such a problem, a microwave oven for driving a magnetron has been developed and used in recent years by using a DC power source made of various means of transportation such as a vehicle or a power battery that can be carried outdoors. A microwave oven is used to convert a DC voltage into an AC by employing a separate inverter.

On the other hand, such a microwave oven typically uses a power supply battery of 12V or 24V as a DC power source, and has a current capacity of 30A to 100A in order to drive the magnetron to an appropriate output by such a DC power source. Therefore, the switch for controlling the power supply to the magnetron according to the door operation of the microwave oven and the function button operation by the user, that is, the primary interlock switch and the secondary interlock switch are directly connected to the power supply. Since it is necessary to control the voltage, a special switching element for a purpose that can withstand the large current of the DC power supply mentioned above should be adopted.

However, in such a microwave oven, a large-capacity switch must be employed to withstand the large current of the DC power supply. However, developing such a large-capacity switch has considerable difficulties with current switch manufacturing technology, and increases the manufacturing cost significantly. There is a problem that this is inevitable.

In addition, in such a microwave oven, even if the master lock switch and the non-interlock switch are installed to control the DC power supply, the interlock regulations required by the microwave standards organization, that is, the master lock switch and the non-interlock switch are caused by an error. Even if the door is opened in the shorted state, it still contains a technical problem of providing a separate safety circuit that satisfies the regulation to prohibit the operation of the magnetron.

In addition, in such a microwave oven, when the DC voltage from the DC power source includes an overcurrent, the voltage drop due to the overcurrent rapidly rises, but such an excessive voltage drop is properly detected to include an inverter circuit. There is no provision of a protection circuit for preventing damage to various circuit elements.

Therefore, in the above-described microwave oven, it is urgently required to employ a protection circuit that satisfies the interlock regulations provided by the standards organization while properly detecting excessive voltage drops due to the generation of overcurrent, thereby preventing damage to the circuit elements. .

Accordingly, the present invention has been made in view of the above-described conventional circumstances, and an object thereof is a direct current microwave oven in which a circuit protection operation for preventing damage to a circuit element is performed in addition to monitoring operation of a monitor switch and detecting occurrence of overcurrent. To provide a safety circuit.

1 is a circuit diagram showing a state in which a safety circuit according to an embodiment of the present invention is applied to a microwave oven.

Explanation of symbols on the main parts of the drawings

HVT: high voltage transformer, HVC: high voltage capacitor,

HVD: High Voltage Diode, MGT: Magnetron,

DSW: door switch, PSW: main interlock switch,

SSW: Negative interlock switch, VFC1, VFC2: Pulse drive circuit,

FET1, FET2: field effect transistor, RY1, RY2: relay,

MSW1, MSW2, MSW11, MSW22: monitor switch,

30: voltage regulator, 40: microcomputer,

50, 51, 53: transistor, 52: op amp,

54: Comparator.

In order to achieve the above object, according to an embodiment of the present invention, the inverter means is driven to convert the DC power into alternating current, a high voltage transformer for generating a high pressure applied to the magnetron by the drive of the inverter means, the inverter A microwave oven comprising a pulse driving means for generating a driving pulse for driving the means, and a switching means for controlling the generation of power of the DC power source according to the opening / closing operation of the cooking chamber door, wherein the cooking chamber is operated when the switching means malfunctions. Safety circuit of a direct current microwave oven is provided, including a switch monitor means for shutting off the power supply of the DC power supply according to the opening and closing operation of the door.

The switch monitor means includes a plurality of monitor switches that are switched according to the opening and closing operation of the cooking chamber door in a short state due to an abnormal occurrence of the switching means, and are opened when a plurality of monitor switches are switched to induce a large current to cut off the DC power. It is preferable to include a fuse.

Preferably, one end of each of the plurality of monitor switches is connected to the DC power supply through a fuse, and the other end thereof is connected between the inverter means and the primary coil end of the high voltage transformer.

It is preferable to further include an overcurrent detection / holding means for receiving the power generated from the DC power supply through the switch monitor means to detect an overcurrent generated from the DC power supply to block the generation of the driving pulse of the pulse driving means. .

In addition, it is preferable that the switch monitor means comprises one stage of switching contacts connected to the DC power supply via a fuse, and the other end of the switching contacts comprises three stages of monitor switches connected to the overcurrent detection / holding means side.

The overcurrent detecting / holding means detects a voltage drop value resulting from overcurrent of the inverter means and generates a detection voltage, and compares the detected voltage from the overcurrent detecting portion with a preset reference voltage and outputs a comparison result signal. It is preferable to include a comparison unit and a feedback unit for continuously generating a feedback voltage exceeding the reference voltage set in the comparison unit.

Preferably, the amplification unit further amplifies the detection voltage from the overcurrent detection unit and applies the amplification unit to the comparison unit.

According to the present invention configured as described above, it is possible to control the operation of the pulse drive circuit for generating a pulse signal for driving the inverter by a small amount of switch operation, by detecting a short state caused by the abnormal occurrence of the switch An overcurrent sensing / maintenance circuit is applied to prevent the destruction of circuit elements by applying a monitor switch to cut off the DC power supply in a three-stage switch structure and detecting the overcurrent generated from the DC power supply through the three-stage monitor switch. By adopting the above, it is possible to satisfy the safety standard of the microwave oven and to prevent damage to the circuit element from generation of overcurrent.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the present invention configured as described above.

1 is a circuit diagram showing a state in which a safety circuit according to an embodiment of the present invention is applied to a microwave oven. As shown in FIG. 1, an embodiment of the present invention includes first and second monitor switches MSW11 and MSW22, first and second transistors 50 and 51, op amps 52, and third. A transistor 53, a diode D1, a pulse driver circuit VFC2, and a comparator 54 built in the pulse driver circuit VFC2.

The first and second monitor switches MSW11 and MSW22 have respective first switching contacts N11 and N21 connected in common with the positive terminal (+) of the DC power supply DC via the fuse FUSE1. Each of the second switching contacts N12 and N22 is connected to the first and second transistors 50 and 51, respectively.

Each of the first and second monitor switches MSW11 and MSW22 has a first switching terminal in a state where the main lock switch PSW and the non-interlock switch SSW are normally switched on / off according to the opening / closing operation of the cooking door. The switching contacts N11 and N21 and the second switching contacts N12 and N22 are switched to the sides.

On the other hand, if an abnormality occurs in the main lock switch PSW and the non-interlock switch SSW, the cooking door is opened in the shorted state, and the switching terminal is switched to the first switching contacts N11 and N21. The fuse FUSE1 is opened by inducing a large current.

On the other hand, each of the first and second transistors 50 and 51 has a base terminal connected to the first and second pulse output terminals OUT1 and OUT2 of the pulse driving circuit VFC2, respectively. In addition, respective collector ends of the first and second transistors 50 and 51 are connected to second switching contacts N12 and N22 of the first and second monitor switches MSW11 and MSW22, respectively. The emitter stage is connected to the ground terminal via the respective resistors R7 and R8.

Next, an operation according to an embodiment of the present invention made as described above will be described in detail with reference to FIG. 1.

First, when the main lock switch PSW and the non-interlock switch SSW are switched on, the pulse driving circuit VFC2 is activated by receiving a DC voltage of 15 V from the voltage regulator 30 to the power supply terminal Vcc. The first and second pulse output terminals OUT1 and OUT2 generate first and second pulse signals in which mutual pulse periods are inverted.

At this time, the first and second field effect transistors FET1 and FET2 are alternately turned on by receiving the first and second pulse signals from the pulse driving circuit VFC2, respectively. The high voltage transformer HVT converts the DC voltage from the DC power supply DC into an AC voltage by alternating switching-on operations of the first and second field effect transistors FET1 and FET2, thereby converting the secondary voltage T2. At high pressure is induced.

Accordingly, the magnetron (MGT) is induced in the high voltage transformer (HVT) is driven by the high pressure backed by the high voltage capacitor (HVC) and the high voltage diode (HVD) is driven to generate a microwave.

Meanwhile, the first and second monitor switches MSW11 and MSW22 have their respective switching terminals connected to the second switching contact points N12 and N22 when the main lock switch PSW and the non stop lock switch SSW are normally operated. It is switched.

At this time, when excessive current is generated in a closed circuit formed by alternating switching-on operations of the first and second field effect transistors FET1 and FET2, the first and second transistors 50 and 51 and the opi By the operation of the amplifier 52 and the comparator 54, the above-described overcurrent is detected.

In addition, the pulse driving circuit VFC2 corresponds to an overvoltage through the diode D1 by a feedback control signal continuously generated through the feedback terminal FB and the continuous switching-on operation of the third transistor 53. The feedback voltage is continuously supplied to the comparator 54, whereby the detection state of the overvoltage is maintained.

Accordingly, the first and second field effect transistors FET1 and FET2 are kept in a switched off state, and as the driving of the magnetron MTG is stopped, the first and second field effect transistors FET1 and FET2 are stopped. The associated circuitry, including, is protected from overcurrent.

Then, when the cooking door is opened while the main lock switch PSW and the non stop lock switch SSW are abnormally shorted due to an abnormal occurrence, the first and second monitor switches MSW11 and MSW22 Since the main lock switch PSW and the non stop lock switch SSW are not normally switched off even when the cooking door is opened, the switching terminals are switched to the first switching contacts N11 and N21.

Accordingly, in the state in which the first and second field effect transistors FET1 and FET2 operate, the main circuit switches MSW11 and MSW22 are switched to the first switching contact N11 and N21 to provide a large current in a closed circuit. Is induced and the fuse FUSE1 on the DC power supply DC side is opened.

On the other hand, even if the first and second transistors 50 and 51 receive the first and second pulse signals from the pulse driving circuit VFC2 at their base ends, the first and second monitor switches MSW11. Since the MSW22 is switched to the first switching contacts N11 and N21, the switching-off state is maintained so that the overvoltage cannot be detected due to the generation of the large current.

The pulse driving circuit VFC2 normally generates the first and second pulse signals to operate the first and second field effect transistors FET1 and FET2 normally, thereby generating a large current to generate the fuse FUSE1. To open it.

As a result, the high pressure is not induced in the high voltage transformer (HVT), the magnetron (MGT) is prohibited from being applied to the high pressure is prohibited from driving.

According to the present invention made as described above, by employing a plurality of monitor switches for detecting a short state caused by the abnormal occurrence of the switch to cut off the supply of the DC power supply to detect the overcurrent generated from the DC power supply, the destruction of the circuit element By adopting an overcurrent sensing / holding circuit that prevents the leakage current, the safety standard of the microwave oven can be satisfied and damage to the circuit element can be prevented from the occurrence of the overcurrent.

The present invention is not limited to the above-described specific preferred embodiments, and various modifications can be made by any person having ordinary skill in the art without departing from the gist of the present invention claimed in the claims. Of course, such changes are intended to fall within the scope of the claims set forth.

Claims (7)

An inverter means driven to convert a DC power source into an alternating current, a high voltage transformer for generating a high pressure applied to the magnetron by driving the inverter means, a pulse driving means for generating a driving pulse for driving the inverter means, and In the microwave oven having a switching means for controlling the generation of the power supply of the DC power source according to the opening and closing operation of the cooking chamber door, Safety circuit for a microwave oven comprising a switch monitor means for shutting off the power supply of the DC power supply according to the opening and closing operation of the cooking chamber door when the switching means malfunction. The method of claim 1, wherein the switch monitor means, A plurality of monitor switches which are switched according to the opening / closing operation of the cooking chamber door in a short state due to an abnormal occurrence of the switching means; The safety circuit of the microwave oven for DC characterized in that it comprises a fuse which is opened when the plurality of monitor switches are switched and a large current is induced to cut off the DC power. The method of claim 2, wherein one end of each of the plurality of monitor switches is connected to the DC power supply via a fuse, and the other end is connected between the inverter means and the primary coil end of the high voltage transformer. Safety circuit of direct current microwave oven. The overcurrent detection / holding means according to claim 1, wherein the power generated from the direct current power source is applied through the switch monitor means to detect an overcurrent generated from the direct current power source to block driving pulse generation of the pulse driving means. Safety circuit of a microwave oven for direct current characterized in that it comprises a further. 5. The switch monitor means according to claim 4, wherein one end of the switching contact is connected to the DC power supply through a fuse, and the other end of the switch monitoring means is composed of three stages of the switch connected to the overcurrent detection / holding means. Safety circuit of direct current microwave oven. The method according to claim 4, wherein the overcurrent detection / holding means is An overcurrent detector for detecting a voltage drop value caused by an overcurrent of the inverter means to generate a detection voltage; A comparator for outputting a comparison result signal by comparing the detected voltage from the overcurrent detector with a preset reference voltage; And a feedback unit for continuously generating a feedback voltage exceeding the reference voltage set in the comparison unit. 7. The safety circuit of a microwave oven according to claim 6, further comprising an amplifying unit which amplifies the detected voltage from the overcurrent detecting unit and applies the amplifying unit to the comparing unit.