KR100301462B1 - Circuit for protecting induction heating cooking utensil - Google Patents

Abstract

PURPOSE: An induction heating cooking utensil protecting circuit is provided to prevent the breakage of a switching device by detecting the operation state of a comparator according to a feedback of an input current. CONSTITUTION: An inverter unit(33) switches alternately a switching device and applies a high frequency current to a working coil to heat a load. An inverter driving unit(34) controls the switching device of the inverter unit(33). An input current detecting unit(35) detects the amount of current inputted to the inverter unit(33). A microcomputer(36) outputs a signal for heating the load and detects whether the load exists or not. An isolating unit(37) isolates the signal outputted from the microcomputer(36) from the power source. A current setting unit(43) changes a current signal level for the inputted signal divided through the dividing unit(37). A normal load determining unit(41) compares the inputted current detecting signal with the set current level to determine whether the compared result is a normal load or not. A start/stop unit(42) controls the operation of a voltage control oscillating unit(39) for controlling the inverter driving unit(34) in response to the output of dividing unit(37). A current feedback unit(38) supplies a control voltage to the voltage control oscillating unit(39) in response to the output of the start/stop unit(42).

Description

Induction Heating Cooker Protection Circuit

1 is a circuit diagram of a conventional induction heating cooker.

2 is an operating waveform diagram of each part according to FIG.

3 is a protection circuit diagram of the induction heating cooker of the present invention.

4 is an operating waveform diagram of each part according to FIG.

5 is one embodiment of FIG.

* Explanation of symbols for main parts of the drawings

31: filter part 32: rectification / smoothing part

33: inverter unit 34: inverter driving unit

35: input current detector 36: microcomputer

37: separation unit 38: feedback unit

39: voltage controlled oscillator 40: time constant

41: comparator 42: start / stop

43: current setting section 44: container

The present invention relates to an induction heating cooker, such as an induction heating cooker, an induction heating cooker, and in particular, in the case of an unsuitable container such as an aluminum or copper container, stops heating or warns a user to prevent destruction of a switching device due to an incorrect operation. It relates to a protection circuit of an induction heating cooker to prevent it in advance.

As shown in FIG. 1, the circuit configuration of the conventional induction heating cooker includes a filter unit 1 that receives commercial power and filters the coils and capacitors to remove noise, and a commercial power source through the filter unit 1. Is rectified and smoothed, and rectified and smoothed to convert into a DC voltage, and an inverter part for heating a load having a vessel by the voltage supplied from the rectified and smoothed part 2. And an inverter driver 4 for alternating switching of the two switching elements of the inverter unit 3, an input current detector 5 for sensing the amount of current input to the inverter unit 3, and a heating cooker. The microcomputer 6 for output control and checking that there is no heating vessel, and the separation unit 7 which transmits a signal while separating power from the microcomputer 6 and each unit controlling the inverter unit 3. ) And a current detection signal detected through the input current detection unit 5 And the current feedback unit 8 for comparing the signal sent from the microcomputer 6 and outputting the control voltage according thereto, and the switching of the inverter unit 3 according to the control voltage output from the current feedback unit 8. A voltage controlled oscillator 9 for determining the switching frequency of the device, a time constant 10 for determining the frequency time constant of the voltage controlled oscillator 9, and a fixed potential or input voltage to detect a small load or no load The comparator which determines whether there is an abnormal state by comparing the two values by inputting the reference voltage Vref and the output of the input current detecting unit 5 which are changed when the fluctuation occurs, and informs the microcomputer 6 of the result ( 11).

Looking at the conventional technology configured as described above are as follows.

When commercial power is input, first, the filter unit 1 filters and removes noise that may be applied to the commercial power by using a coil and a capacitor, and then provides the current / smoothing unit 2.

Then, in the rectifying / smoothing unit 2, rectification is performed using a bridge diode BD, and smoothing is performed using a smoothing choke coil L1 and a smoothing capacitor C2. Deliver to wealth (3).

In this case, the inverter driving unit 4 alternately switches the switching elements Q1 and Q2 of the inverter unit 3 to apply a high frequency current to the working coil L2 and the resonant capacitor C5 and C6, thereby providing the walking. As the high frequency current flowing through the coil L2 is induced in the container 12 to generate Joule heat, the container 12 is heated.

The output applied to the vessel 12 is represented by the current transformer 51 and the rectifier 52. When the amount of current is changed to a magnitude in the current transformer 51 of the input current sensing unit 5, the rectifier 52 Rectify and transfer to the current feedback unit (8).

Accordingly, the current feedback unit 8 compares the current sensing signal detected by the input current sensing unit 5 with the signal level given by the microcomputer 6, and changes the frequency according to the comparison state. Give cont signal to 9).

Then, the voltage controlled oscillator 9 determines the frequency by the time constant determined by the time constant 10 and the cont signal transmitted from the current feedback unit 8.

If there is no load on the working coil L2, the current flowing through the switching element Q1 and the freewheel diode D1 of the inverter unit 3 is equal to the second (c), and the switching element Q2 ) And the freewheel diode (D2) is the same as the second (d), and if you look at this waveform in detail, the current flows in reverse to the freewheel diode by the amount of current flowing through the switching element is very small.

That is, a minute current is sensed by the input current detector 5 so that the output of the comparator 11 goes low.

The low state output of the comparator 11 is transmitted to the microcomputer 6 via the separator 7.

Accordingly, the microcomputer 6 recognizes that it is an object.

At the normal load, the current flowing through the switching element Q1 and the freewheel diode D1 has a waveform as shown in FIG. 2 (a), and the current flowing through the switching element Q2 and the freewheel diode D2 is represented by the second ( b) It is the same as the waveform shown in the figure. Looking at the waveform, the current flowing in the switching element is much larger than the current flowing in the freewheel diode. It means that the energy is delivered to the container well and is normally heated.

However, if the container 12 is made of aluminum (AL) or copper, the currents flowing through the switching elements Q1 (Q2) and the freewheel diodes (D1) (D2) are not shown in the second (e), (f) degrees. The same waveform is obtained, but the amount of current flowing through the switching element and the amount of current flowing through the freewheel diode are almost the same, but the absolute magnitude thereof becomes very large, which may lead to the destruction of the switching element beyond the absolute power of the switching element.

In order to prevent this breakdown, it is necessary to carry out the detection of small items and proper containers in a very short time to prevent the loss of the set. However, the detection time of too small a moment has a problem such as malfunction of microcomputer or inability to detect.

Therefore, the object of the present invention is to switch the oscillation frequency to increase the minimum oscillation frequency under the control of the time constant unit so as to easily detect that there is no load, the small load and the inadequate heating vessel, and to stop the set operation by stopping the set operation. To provide a protection circuit of an induction heating cooker.

It is another object of the present invention to provide a protection circuit of an induction heating cooker which detects the operation state of the comparator according to the feedback amount of the input current during normal operation and stops the operation during the low voltage protection and overvoltage to prevent the damage of the set. It is for.

The protection circuit of the induction heating cooker according to the present invention for achieving the above object, as shown in Figure 3, receives a commercial power supply to filter the coil and capacitor to remove noise that can be applied to the power supply 31 And rectification / smoothing unit 32 for rectifying and smoothing commercial power, from which noise is removed, through the filter unit 31 to a DC voltage, and a DC voltage supplied from the rectifying / smoothing unit 32. The inverter unit 33 for heating the load, the inverter driver 34 for outputting a signal for alternately switching the switching elements of the inverter unit 33, and the current input to the inverter unit 33 Input current detecting unit 35 for sensing the amount, the microcomputer 36 for controlling the output of the load, determine whether there is a load, and outputs the control output accordingly, and the signal output from the microcomputer 36 power Separation unit 37 for separating, the current setting unit 43 for changing the current level signal with respect to the input signal separated through the separation unit 37 and the input current detection unit 35 sensed by The normal load determination unit 41 compares the current detection signal and the current level changed by the current setting unit 43 to produce a positive or negative output, and the inverter driver 34 according to the output of the separation unit 37. A start / stop unit 42 for controlling the operation of the voltage controlled oscillator 39 for controlling the current, and a current feedback for supplying a control voltage to the voltage controlled oscillator 39 according to the output of the start / stop unit 42. It consists of a part 38.

Referring to the operation and effects of the present invention configured as described above in detail.

When the commercial power is input, first, the filter unit 31 filters the coils and the capacitors to remove noise that may be applied to the commercial power source, and outputs the noise to the rectifying / smoothing unit 32.

In the rectifying / smoothing unit 32, rectification is performed using the bridge diode BD11, and smoothing is performed using a smoothing choke coil L11 and a smoothing capacitor C32 to make a DC voltage. To be delivered.

At this time, the switching elements Q31 and Q32 are alternately switched by the control of the inverter driver 34 to apply a high frequency current to the working coil L31 and the resonant capacitor C35 and C36, thereby providing the working coil L31. As the high-frequency current flowing through the container 44 is induced to generate Joule heat, the container 44 is heated.

At this time, when the microcomputer 36 first sends a high signal to its output port B, the signal passing through the separation unit 37 is applied to the start / stop unit 42 through the diode D35 and at the same time set the current. The divided voltage by the ratio of the resistors R36 (R37) of the negative 43 is applied to the positive side of the comparator COMP1 of the steady load determining unit 41.

At this time, the comparator COMP1 receives the current sensing signal detected by the input current sensing unit 35 to its negative side.

Therefore, the comparator COMP1 compares the current sensing signal with the signal set by the microcomputer 36 and outputs the same.

When the high signal applied to the start / stop section 41 is inverted through the inverter I1 and output to the base of the transistor Q3, the power supply voltage of the current feedback section 38 is turned off as the transistor Q3 is turned off. The resistor R31 is applied to the input terminal CONT of the 555 timer constituting the voltage controlled oscillator 39 to oscillate.

In this way, when the oscillation frequency is outputted to the output terminal OUT thereof, as described above, the inverter driver 34 alternately turns on or off the switching elements Q31 and Q32 to heat the container 44.

At this time, the oscillation frequency for oscillation is determined by the minimum oscillation frequency by the time constants of the resistors R32 and R33 and the capacitor C38 of the time constant part 40.

In general, the time constant is given to have an oscillation frequency twice that of normal (at maximum output).

Then, the current waveforms by the switching elements Q31, Q32 and the diode D3l of the inverter unit 33 are as shown in FIG. 4. The initial load check time has an oscillation frequency of about 40 KHz and the waveform under normal load. Is the same as the fourth (a), at no load is the same as the fourth (b), and in the case of aluminum or copper vessel is the same as the fourth (c).

That is, under normal load, the amount of current flowing through the switching elements Q31 and Q32 is considerably larger than the amount flowing backward by the diode D3l, so that the amount of input power current becomes large.

At this time, since the normal load determination unit 41 operates periodically, the microcomputer 36 confirms that the C output port level is normal.

If there is no load or an unsuitable container, the amount of input current decreases as it flows backward from the diode by the current flowing through the switching element.

The normal load determination unit 41 does not operate and the microcomputer 36 detects this.

In this case, the oscillation frequency is more than doubled than normal so that the maximum current does not exceed the specification of the switching element (SPEC) even in an unsuitable container.

When it is determined that there is a normal container initially as shown in FIG. 4 (a), the microcomputer 36 outputs a high signal to the output port A thereof, and converts the capacitor value of the time constant part 40 to the capacitor C38. (C39) raises the switching frequency to lower the switching frequency and enters the normal operating area, and the signal (CONT) level input to the 555 timer in the voltage controlled oscillator 39 to operate at a constant output by the normal load determiner 41. Adjust by feeding back.

When the input is too high or low, the signal of the normal load determination unit 41 is absent or too much operation, and the microcomputer 36 stops the recognition operation as a low voltage or an over voltage.

As another embodiment, as shown in FIG. 5, instead of the capacitors C38 and C39 connected in parallel in the time constant unit 40, one capacitor C39 is initially set so that the minimum oscillation frequency is high so that no load is obtained. Check for small loads and unsuitable heating containers.

As described in detail above, the present invention initially switches the oscillation frequency by increasing the oscillation minimum frequency under the control of the time constant part, thereby making it easy to detect no load, small load, and inadequate heating container, thereby preventing set breakage and operating normally. In the meantime, the comparator's operation state is detected according to the feedback amount of the input current to protect the low voltage and stop the operation during overvoltage, thereby preventing set breakage.

Claims (5)

An inverter unit for heating the load by applying a high frequency current to the working coil by alternately switching the switching elements when the DC voltage is input through the filtering means and the rectifying / smoothing means, and an inverter driving means for controlling the switching elements of the inverter unit; Input current sensing means for sensing the amount of current input to the inverter unit, a microcomputer for outputting a signal for heating the load and to detect the presence of a load, and a separation for separating the power output from the signal output from the microcomputer Means, current setting means for changing a current level signal with respect to an input signal separated through said separating means, normal load determination means for comparing the input current sensing signal with a set current level to determine whether it is a settled load; Operation of the voltage controlled oscillating means for controlling the inverter driving means in accordance with the output of the separating means Control start / stop means, and the protection circuit of the induction heating cooker according to claim consisting of a control voltage to the voltage controlled oscillator means in accordance with output of the start / stop means in the feedback current by means of supply. The protection circuit of an induction heating cooker according to claim 1, wherein the voltage-controlled oscillating means comprises 555 timers. The protection circuit of an induction heating cooker according to claim 1, wherein the normal load determining means comprises a comparator. The protection circuit of an induction heating cooker according to claim 1, wherein the time constant determining means determines the time constant with a capacitor connected in parallel to adjust the value by a resistor and an external signal. 2. The protection circuit of an induction heating cooker according to claim 1, wherein the time constant determining means connects a resistor and one capacitor so that a minimum oscillation frequency is initially high.