KR940003232B1 - Automatic voltage apparatus of microwave oven - Google Patents

Abstract

The voltage selection switch operates automatically by the input power voltage and is not affected by the high frequency component of input current. The voltage selection switch system includes a voltage detector (6) for generating two kinds of signal which is determined by the rectified voltage level so that the kind of input voltage is detected by a microcomputer, a reset (5) for resetting a microcomputer by the filtered input voltage level, a switch (8) operated by a control signal transmitted from a microcomputer to change internal circuit by the input voltage level, and a power supply (7) for providing power to the switch (8).

Description

Automatic voltage changer of microwave oven

1 is a detailed circuit diagram of a conventional automatic voltage switching device.

2 is a detailed circuit diagram of the automatic voltage switching device of the present invention.

3 is an operational flowchart of the present invention.

* Explanation of symbols for main parts of the drawings

1: microcomputer 2: inverter

3: magnetron 4: power supply

5: Reset unit 6: Voltage sensing unit

7: constant voltage unit 8: switching unit

9: Fan Motor BD ₁ ~ BD ₂ : Bridge Diode

C ₁ ~ C ₈ : Capacitor D ₁ ~ D ₇ : Diode

HVT ₁ : high voltage transformer LVT ₁ : low voltage transformer

Q ₁ to Q ₆ : Transistors RY ₁ to RY ₃ : Relay

ZD ₁ to ZD ₃ : Zener Diode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic voltage switching device for a microwave oven capable of automatically switching a used AC power source (100 V / 220 V) applied to a microwave oven. In particular, in a microwave oven in which an inverter is built, malfunction due to a high frequency current that is noise This will not happen.

The conventional automatic voltage switching device of the microwave oven was to be able to switch the power supply (100V / 220V) automatically without the service of changing the wiring inside the device when using the microwave oven in the commercial voltage (100V / 220V).

1 is a detailed circuit diagram of an automatic voltage switching device according to the prior art, a capacitor (C ₂₀ ) connected to an input terminal (a) of an AC commercial AC power supply (100V / 220V) and inducing a voltage according to a commercial voltage applied thereto; the capacitor (C ₂₀₎ and fuses (F ₂₀₎ of the input terminals (a, b) connected to and made of a four diode capacitor bridge diode (DB ₂₀₎ for full-wave rectification of the voltage induced in the (C ₂₀₎ through And a resistor (R ₂₁ , R ₂₂ ), a diode (D ₂₀ ), and a capacitor (C ₂₁ , C ₂₂ ) and the diode (D ₂₀ ) and a capacitor (C ₂₂ ) of the bridge diode (DB ₂₀ ). Smoothing unit 10 for smoothing the full-wave rectified signal, transistors Q ₂₀ , Q ₂₁ , resistors R _23- R ₂₆ , zener diodes ZD ₂₀ , ZD ₂₁ , and capacitor C ₁ ) led by the transistor (Q ₂₀₎ and a resistor (R _24, R ₂₅₎ and zener diode (ZD ₂₀₎ for said smoothing power adjusted to about 48V by the DC This negative back transistor (Q ₂₁₎ and a resistor (R ₂₆₎ and the Zener diode voltage adjusting section 11 for down-adjusted to about DC24 by (ZD ₂₁₎ and an operational amplifier (OP ₂₀₎ and a resistor (R ₂₇ -R ₃₁ ) And a diode (D ₂₁ ) and a capacitor (C ₂₄ ), and the output signal of the smoothing unit 10 is distributed through the resistors R ₂₇ and R ₂₈ to divide this divided voltage as a reference voltage. A voltage sensing circuit 12 for sensing the magnitude of the commercial voltage inputted by comparing the divided voltage of the resistors R ₂₉ and R ₃₀ for distributing the 24V output voltage of 11) with the operational amplifier OP ₂₀ , and the voltage It is connected to the output side of the sensing circuit 12 and consists of a continuous amplifier (OP ₂₁ ), resistors (R _32- R ₃₇ ), diodes (D ₂₂ , D ₂₃ ) and a capacitor (C ₂₅ ) and the voltage sensing circuit 12 wherein the resistance of the output signals _{(R 32, R 33, R} 36) and a reference voltage distribution of the capacitor (C ₂₅₎ and delays the delayed signal and a resistor (R _36, R ₃₇₎ with And a delay and comparator circuit 13 for output as compared to the pressure through the operational amplifier (OP _21), the delay and comparison circuit 13, an output transistor (Q ₂₂₎ for driving the relay (RY ₂₀₎ in accordance with the said transistor (Q _22), turned on and turned off the low-pressure transformer (LVT ₂₀₎ of 110V tab or relay to select the 220V tab (RY ₂₀₎ and the relay (RY ₂₀₎ the relay (RY ₂₀₎ when not operated by Dummy resistor (R ₄₁ ) for consuming the same current as, a transistor (Q ₂₃ ) for switching the function of the dummy resistor (R ₄₁ ), and the relay (RY ₂₀ ) is operated to the state of the circuit the transformer is composed of a low-pressure relay which is driven by excitation voltage (110Vac) it applied to the primary coil of the low-voltage transformer (LVT ₂₀₎ when selected from the 220V 110V tab of tab _{(LVT 20) (RY 21)} .

The basic concept of the conventional circuit detects and inputs a voltage level across the resistance sum R 'by the sum R' of the capacitor C ₂₀ and the other circuits when an AC voltage of a commercial frequency is applied. It is configured to detect whether the commercial voltage is 110V or 220V, and determines whether the tap of LVT ₂₀ is normally set to 220V or switched to 110V.

In FIG. 1, the current I flowing through the dummy resistor R ₄₁ by DC 48V from the voltage adjusting unit 11 is 10 mA, and when the commercial voltage input is AC 110 V / 60 mA, the capacitor ( The voltage at both ends of C ₂₀ ) becomes about AC 56V by the following equation (1).

V _C1 = I / jwc... … … … … … … … … … … … … … … … … … … … (One)

Here, C = 0.68 ms, W = 2 pi f = 120 pi, and I = 100 ms.

On the other hand, if the commercial voltage input under the same condition is AC 220V / 60㎐, the voltage at both ends of the capacitor C ₂₀ is the same, so the voltage V _{A at} the output point A of the bridge diode BD ₂₀ is the input voltage. It appears differently depending on whether it is 110V / 60㎐ or 220V / 60㎐.

Therefore, the voltage V _A can only be determined experimentally.

The voltage V _A is divided by the resistors R ₂₇ and R ₂₈ of the voltage sensing circuit 12 and compared with the divided voltage of the resistors R ₂₉ and R ₃₀ , which are reference voltages, in the operational amplifier OP ₂₀ . .

That is, when the input voltage is AC 110V, the high signal is output through the operational amplifier OP ₂₀ , and when the AC voltage is 220V, the low signal is output.

When AC 110V is input, the output signal of the operational amplifier OP ₂₀ of the voltage sensing circuit 12 is supplied to the resistors R ₃₂ , R ₃₃ , R ₃₅ and the capacitor C ₂₅ of the delay and comparison circuit 13. by the operational amplifier (OP ₂₁₎ is to output a high signal to a high signal to the switching transistor (Q ₂₂₎ a by the relay (RY ₂₀₎ for driving by the relay (RY ₂₀₎ causes a low pressure transformer (LVT ₂₀₎ in the on while delayed Select the primary side tap for 110V.

Thus, each part of the circuit is configured to fit 110V.

On the contrary, in the case of the input voltage AC 220V, the output of the operational amplifier OP ₂₀ of the voltage sensing circuit 12 goes low, so that the charge accumulated in the capacitor C ₂₅ of the delay and comparison circuit 13 becomes a resistance R _34. And discharged through the diode D ₂₂ and lower than the signal input to the non-inverting input terminal (+) of the operational amplifier OP ₂₁ .

Therefore, the output signal of the operational amplifier OP ₂₁ goes low, so that the relay RY ₂₀ maintains its initial state and the low voltage transformer LVT ₂₀ maintains the 110 V tap, which is the initial state by the relay RY ₂₀ . Done.

That is, in the initial stage, all the circuits maintain the wiring state corresponding to 220V, and when the input commercial voltage is changed to 110V, the circuit state is automatically switched to the wiring state corresponding to 110V safely without manual wiring change.

As described above, the conventional technology relies on the capacitor C ₂₀ as a means for lowering AC 110V or 220V to DC 48V and DC 28V for automatic voltage switching to a microwave oven or to obtain a driving power of a relay.

However, the current flowing through the capacitor C ₂₀ or the voltage between both ends is related to the frequency applied to the capacitor C _20. Thus, the external noise (eg, a high frequency noise generated by a mixer or a hand drill and a high frequency current of an inverter microwave oven) The voltage across the capacitor C ₂₀ was not constant.

That is, in FIG. 1, when the voltage V A of the point _A is shaken by the high frequency noise, the voltage sensing circuit 12 confuses the commercial voltage input and malfunctions so that the connection of the device is changed and eventually the device is broken. There was a problem.

The present invention is to eliminate the above problems, it is possible to maintain the initial power supply state to the end even if there is a fluctuation by external noise by using the appropriate software, as well as the automatic configuration of the microwave oven, which can reduce the cost by simplifying the configuration of hardware. The object is to provide a voltage switching device.

In order to achieve the above object, the present invention rectifies and smoothes two types of commercial voltage inputs and operation voltages, and includes a predetermined magnetron and sets the initial state of the circuit to one of two types of commercial voltages. According to the present invention, a power supply unit for supplying a microcomputer as a driving voltage according to a predetermined voltage and then rectifying and smoothing the two kinds of commercial voltages by a predetermined ratio, and according to the magnitude of the smoothed signal in the power supply unit A voltage sensing unit for outputting two signals of different types to the microcomputer so that the microcomputer recognizes the type of a commercial voltage, and is switched by a control signal of the microcomputer to be output in correspondence with an output signal of the voltage sensing unit; Maintain or convert the circuit structure in the inverter to suit the input commercial voltage Creating a constant voltage to input the rectified signal of the switching unit, the power supplier for Pointing includes adding a constant voltage to maintain it stably supplied to the switching driving voltage portion.

This will be described with reference to the accompanying FIG. 2 as an embodiment.

2 is a detailed circuit diagram of the present invention, which is connected to a commercial voltage input terminal (a) and (b), and has a low voltage transformer LVT ₁ and a bridge diode BD to down the commercial voltage 110V / 220V to a predetermined ratio. ₁ ) a power supply unit 4 consisting of a resistor R ₁ , a capacitor C ₁ , a diode D ₁ , and a voltage regulator IC ₁ (here IC7 805 is used), and an output side of the power supply unit 4. It is connected between and the microcomputer (1) and consists of a zener diode (ZD ₁ ), resistors (R ₂ -R ₄ ), transistors (Q ₁ ) and capacitor (C ₂ ), when the commercial voltage (110V) is input A reset section 5 for applying a reset signal to the reset terminal RST of (1), connected between the power supply section 4 and the microcomputer 1, and a zener diode ZD ₂ and a resistor R; ₅ -R ₇ ), transistor (Q ₂ ) and condenser (C ₃ ). When 110V input, high level continuous level is input to input terminal (Pin) of microcomputer (1). Connected to the voltage sensing section 6 and the commercial voltage input terminals a and b for applying a pulse signal of the capacitor, the capacitors C ₅ and C ₆ , the diodes D ₄ and D ₅ , and the transistors Q ₅ and Q _6. ) And a high voltage transformer (HVT ₁ ) for boosting and outputting a commercial AC voltage input through a bridge diode (BD ₁ ), a capacitor (C ₅ , C ₆ ) and a coil (L ₁ ) to a predetermined DC high voltage. Inverter (2), the magnetron (3) for receiving the driving voltage from the inverter (2) through the capacitor (C ₇ ) and diodes (D ₆ , D ₇ ) and outputs a high frequency signal, It is connected to output terminal (Pout) and consists of transistor (Q ₄ ), resistor (R ₁₀ , R ₁₁ ), diode (D ₃ ) and relay (RY ₁ -RY ₃ ). is turned off by the switch signal, each relay (RY RY _1a ~ _3a) held in the initial state, the initial state and a state and 220V half of each switch relay (RY RY _1a ~ _3a) when 110V input Connected between the switching portion 8, a fan motor 9, the power supply (8) and a Zener diode (ZD ₃₎ and a transistor (Q ₃₎ and a resistor (R _8, R ₉₎ and a capacitor for switching in the state (C ₄ ) and a diode (D ₂ ) and the constant voltage unit for stably lowering the rectified voltage in the power supply unit 4 to a predetermined voltage to stably apply to the relay (RY ₁ ) of the switching unit 8 ( It is composed of 7).

Here, the relays RY ₂ and RY ₃ of the switching unit 8 are each relay switch RY _1a to an excitation voltage of 110 V which is applied to the primary coil of the low voltage transformer LVT ₁ in the power supply unit 4. RY _3a ) is connected to the terminal to automatically switch.

As described above, the present invention is constructed in consideration of low power consumption of the microcomputer 1, and the terminals of each of the relay switches RY _1a to RY _{3a in the} initial state are located at a position corresponding to 220V.

If 110V is input through the commercial voltage input terminals a and b, the secondary bridge diode BD ₁ , the smoothing capacitor C ₁ , and the diode D of the low voltage transformer LVT _{1 in} the power supply unit 4 are supplied. _The voltage after ₁ ) is about DC 14V.

This voltage becomes about DC 5V through the voltage regulator IC ₁ and is applied as a driving voltage to the terminal Vcc of the microcomputer 1.

Subsequently, the DC 14V turns on the zener diode ZD ₁ of the reset unit 5 and the transistor Q _{1 in} order to make the reset terminal RST of the microcomputer 1 low.

Therefore, the microcomputer 1 performs the same operation as the pull chart of FIG.

That is, since the commercial voltage input is 110V, the full voltage of the bridge diode BD ₁ does not exceed the voltage wall of the zener diode ZD ₂ in the voltage sensing unit 6, thereby preventing the transistor Q ₂ from conducting. .

Therefore, a high state signal is always input to the input terminal Pin of the microcomputer 1, and the high signal is output through the output terminal Pout after the microcomputer 1 checks this level for a predetermined time.

This high signal turns on the transistor Q ₄ and the relay RY ₁ in the switching section 8 in turn, and the voltage input terminal (a) (b) and the low voltage transformer LVT _{1 in the} power supply section 4 are turned on. The relay switch RY _1a is connected to the 110V terminal from the initial 220V terminal.

From this time, the primary tap of the low voltage transformer LVT ₁ is connected to the 110V side, and the bridge diode BD ₁ outputs about DC 30V.

This voltage is now turned on and off the transistor Q ₂ of the voltage sensing unit 6 to apply a pulse to the input terminal (Pin) of the microcomputer 1, the microcomputer 1 ignores this and the relay (RY ₁ ) By continuing to turn on the microwave will perform a stable operation.

In addition, when 220V is input through the input terminals (a) and (b), approximately DC 29V is supplied to the input side of the voltage regulator IC _{1 in the} power supply unit 4 as opposed to the case described above, and the voltage sensing unit 6 Through the pulse signal is supplied to the input terminal (Pin) of the microcomputer (1).

At this time, the microcomputer 1 counts the number of pulses at regular intervals and keeps the output terminal Pout low.

Thus, the circuit is prevented from switching to the 110V state and the circuit is stably operated at the 220V state.

In other words, according to the present embodiment, the latch power is implemented in a hardware configuration, and according to the present embodiment, the maximum power consumption of the voltage regulator IC ₁ of the power supply unit 4 is 125 kW, and the transistor in the constant voltage unit 7 is implemented. The maximum power consumption of (Q ₃ ) is 180 ㎷, and no excessive heat is generated.

Here, the switching speed of the relay RY ₁ of the switching unit 8 is usually within 10 msec, and the capacitance of the capacitor () in the constant voltage unit 7 is determined so that the following equation (2) is satisfied.

Since the power failure holding time of the microcomputer 1 is usually 100 msec, it is suitable for the current consumption of the microcomputer 1, and the capacitance of the capacitor C _{4 in} the power supply unit 7 is selected so that it cannot be reset.

The above embodiment is applied to a microwave oven, but the automatic voltage switching device of the present invention can be applied to any electric electronic device using a microcomputer.

As described above, the present invention has the following effects.

First, the conventional automatic voltage switching device composed only of hardware is configured by simple hardware by using a software latch function, thereby reducing the cost of the product.

Second, in the conventional hardware configuration, the latch function is released by external noise, and the device may malfunction. However, according to the present invention, reliability is improved because there is no influence of noise.

Claims (1)

A commercial voltage input in which the microcomputer 1 for operation control, the inverter 2, and the magnetron 3 are set to a state corresponding to one of two types of AC commercial voltages into which the initial state of the circuit is input. After rectifying and smoothing in turn, a power supply unit 4 for generating a predetermined voltage and applying it as a driving voltage to the microcomputer 1, and two different types according to the magnitude of the signal rectified in the power supply unit 4 The microcomputer 1 is reset or initialized according to the magnitude of the smoothed signal in the voltage sensing unit 6 and the power supply unit 4 which outputs a signal to the microcomputer so that the microcomputer 1 detects the type of commercial voltage. A reset unit 5 for maintaining the state, and a plurality of switching elements, and is switched by the control signal of the microcomputer 1 which is output corresponding to the output signal of the voltage sensing unit 6 to input the entire circuit configuration Commercial voltage Switching unit 8 to be properly maintained or converted, the constant voltage unit for inputting the rectified signal in the power supply unit 4 to generate a constant voltage and to maintain it stable to supply the switching unit 8 as a driving voltage Automatic voltage switching device of the microwave oven, characterized in that it comprises a (7).