KR200358192Y1 - A circuit sensor for sensing power-drop and an inductive heating cooker including the circuit sensor - Google Patents

Abstract

The present invention relates to a power drop detection circuit and an induction heating cooker having the same to prevent burnout of the power device in the induction heating circuit due to instantaneous power failure (power supply drop). The power drop detection circuit according to the present invention connects a capacitor capable of detecting a transient current between a terminal of a direct current power source (VDC) supplied to a terminal power unit in an induction heating circuit and a common ground terminal (power supply side). When a transient current occurs due to an instantaneous power failure, the transient current flows through the capacitor, so that the transient phenomenon can be quickly detected, thereby preventing the power device in the induction heating circuit from being burned out by the transient current.

Description

A circuit sensor for sensing power-drop and an inductive heating cooker including the circuit sensor}

In an induction heating circuit embedded in an induction heating cooker, a DC power supply (VDC) supplied to the terminal power unit is generally supplied through a smoothing circuit composed of choke coils and capacitors by rectifying commercial AC power. √2 times of AC power.

However, if a power drop phenomenon occurs during the operation of supplying power to the induction heating cooker, that is, an instantaneous power failure phenomenon in which the input power is cut off and then supplied again, it is supplied to the power device by the back electromotive force generated from the choke coil in the induction heating circuit. The direct current voltage value increases momentarily and may damage the power device.

In order to prevent power element damage in the induction heating circuit caused by the counter electromotive force, conventionally, the DC voltage supplied to the power device is monitored, and when it rises above a predetermined limit value, the brake circuit is operated to operate the induction heating circuit. The situation is to take the action to stop immediately. However, this method is performed after the voltage has already risen enough to damage the power device, so the result is far short of what was originally intended.

1 is a block diagram of a circuit for detecting such a conventional overvoltage. In FIG. 1, the overvoltage sensing resistor 71 and the divided resistor 73 divide a DC power supply voltage VDC of several hundred volts to a low value, and the divided voltage value is divided into an abnormal state holding unit through the diode 72. 30), it is compared with the reference voltage VREF. As a result of the comparison, when the divided voltage Y7 is higher than the reference voltage VREF, the output of the comparator 35 becomes high HI. When the output of the comparator becomes high, the transistor 54 of the on / off and hold release section 50 is turned on to pull the oscillation output Q low (LO). It is a principle to stop the operation of induction heating cooker.

Figure 2 shows a graph of the voltage signal waveform at each measurement terminal (VDC, Q, VRS) of the conventional induction heating circuit as described above. For the sake of clarity, the case where there is no operation of the overvoltage protection is taken as an example. Looking at the 'DC waveform' in the graph of Figure 2, it can be seen that the VDC voltage rises very high when the power is re-supplied during the power drop (DROP) period, which is a smooth circuit as described above This is because of the transient phenomenon due to the counter electromotive force of the choke coil 13 to be constructed. As a result of the transient phenomenon, the VDC voltage rises significantly. In this case, if the induction heating cooker continues to operate, the resonance voltage VRS excessively rises as shown in the 'VRS' graph. As a result, the power device 18 at the end portion cannot withstand the withstand voltage and eventually becomes damaged.

FIG. 3 is a graph illustrating an abnormal operation according to a conventional configuration method. In FIG. 3, only a power drop (DROP) section is enlarged and reconstructed. Since the overvoltage detection output Y7 is obtained through the resistors 71 and 73 from the DC power supply VDC terminal, a waveform having the same shape as the DC power supply terminal without phase change is obtained. The important point to be shown in this graph is that the brake is operated because the gradient of the overvoltage sensing output Y7 in the transient phenomenon is gentle and the reference voltage VREF, which is a threshold value for operating the brake circuit, is set high. The power element 18 of the terminal is conducting at least once or twice before being terminated so that the resonance voltage VRS exceeds the allowable upper limit. When the resonance voltage VRS exceeds the allowable upper limit in this manner, the power device 18 of the terminal portion cannot withstand the insulation breakdown voltage and eventually becomes damaged.

In this case, in principle, if the reference voltage (VREF) is set to a low value, the operation of the brake circuit may occur early, and the protection purpose of the power device may be achieved. However, the voltage operating range of the device may be reduced, thereby not satisfying the specification. Another problem arises.

As a result, the fundamental countermeasure is to detect the sudden and excessive voltage rise of the DC power supply terminal VDC more quickly without abnormally lowering the reference voltage value, and to activate the brake circuit before the transient voltage damages the power device. To stop the operation of the circuit.

In order to achieve the above object, the present invention has an object to provide a power drop detection circuit that can prevent the power device from being damaged in the event of a transient power failure in the induction heating circuit, that is, a power drop.

Another object of the present invention is to provide an induction heating cooker which can be safely used even when a transient phenomenon caused by power drop occurs by mounting the power drop detection circuit in an induction heating cooker.

Another object of the present invention will become more apparent from the following detailed description and accompanying drawings.

1 is a block diagram of a conventional power drop detection circuit.

FIG. 2 is a graph of output waveforms at a DC power supply (VDC), oscillation output (Q), and resonant waveform (VRS) terminals when the circuit of FIG. 1 operates. FIG.

3 is an enlarged graph illustrating a section in which a power drop occurs in the graph of FIG. 2;

4 is a block diagram of a power drop detection circuit according to the present invention.

5 is a graph illustrating output states of a power drop detection unit, an abnormal state holding unit, an oscillation output, and a resonance waveform during the circuit operation of FIG. 4;

(Explanation of symbols for the main parts of the drawing)

11 commercial AC power input 12 rectifier diode

13: choke coil 14: smoothing capacitor

16: induction heating coil 17: resonant capacitor

18: power device (IGBT) 31: reference voltage

35: comparator 21: transient sensing capacitor

71: overvoltage detection resistor

Power drop detection circuit of the present invention for achieving the above object, the rectifier diode for rectifying the AC power; A smoothing circuit unit having one end connected to the rectifying diode to smooth the rectified power; A resonant circuit part and a power drop detector connected at one end to the other end of the smooth circuit part; One end is connected to the other end of the power drop detection unit includes an abnormal state holding unit for outputting and maintaining a high (HI) value when a voltage value of more than the reference voltage value (VREF) is input from the power drop detection unit, the power drop The sensing unit detects a power drop when the transient current is conducted to a capacitor connected to one end of the smoothing circuit unit when a transient current occurs due to the power drop.

The present invention emphasizes the phenomenon that the phase of the transient current flowing in the element portion is significantly larger than the rising voltage phase in view of the characteristics of the configuration, and detects the rise of the transient current using the charging characteristic of the capacitor, thereby enabling the brake circuit to operate. It provides an induction heating cooker with improved reliability.

4 is a configuration diagram of an induction heating circuit including a power drop detection unit according to the present invention, and the detailed operation principle thereof is as follows.

The commercial AC power source 11 is converted into a direct current from the rectifying diode 12, and then passes through a choke coil 13 and a smoothing capacitor 14 to a resonant circuit having an induction heating coil 16 and a resonant capacitor 17 in parallel. Is applied.

The oscillation frequency control and oscillation output unit 40 receives the output determination signal P2 from the microcomputer 80, and oscillates at a frequency corresponding to a desired output and passes it to the buffer unit 60. The buffer unit 60 serves to transfer the input signal to the power device 18 by simply amplifying the current.

The on-off and hold-release unit 50 receives an ON or OFF signal P1 from the microcomputer 80 to drive the transistor 51, and the oscillation output Q through the diode 53. ) It acts to interrupt the operation of the induction heating cooker by pulling or releasing to low and to release it when the output (Y3) of the abnormal state hold part is held high (HI). . In the hold state, the hold signal Y3 turns the transistor 54 on, and pulls the oscillation output Q low to stop the operation of the induction heating cooker. If you leave it, it will stay there. Therefore, in order to operate the induction cooker again, the hold state must be released. In order to do so, the transistor 51 needs to be turned on once and then released. When the transistor 51 is turned on, the abnormal state hold output Y3 is forced to be low through the diode 52, and the non-inverting input terminal of the comparator 35 is provided through the diode 33. By removing the voltage applied to the positive (+), the comparator 35 is released from the hold state.

The abnormal state holding part 30, as its name suggests, serves to maintain the abnormal state, because the abnormal signal generally occurs momentarily and then disappears. The reference voltage VREF is set at the inverting input terminal (-) of the comparator 35, and an abnormal signal received from the outside is applied to the non-inverting input terminal (+), so that the output is higher when it is higher than the reference voltage VREF. It is configured to hold to HI. The action of holding the output here is achieved by the diode 33. The resistor 34 is needed for pull up because the output of the comparator is an open collector.

The power drop detector 20 provides a method for detecting when a DC power supply voltage (VDC) voltage is transient, and its configuration and operation are as follows.

When a power drop phenomenon, also called a momentary interruption, occurs, a transient current caused by this flows through the capacitor 21 of the power drop detection unit, and the current path resistor 23 converts the current flowing through the transient current sensing capacitor 21 into a voltage to convert a diode ( It transmits to the abnormal state holding part 3 through 22). The discharge diode 24 serves as a discharge passage when the charge of the transient sensing capacitor 21 is discharged.

5 is an enlarged graph of a power drop (DROP) portion, showing a state in which a safe operation according to the application of the present invention. In the graph 'Power Drop Detection Part Output (Y2)', you can see that the detection waveform rises much faster than the conventional one when the power is turned on again after the DROP, which is very desirable. This is possible because the charging characteristic of the transient current sensing capacitor 21, which is a feature of the present invention, is used. In other words, unlike a resistor, a capacitor has a property that almost all current flows at the moment when a voltage is applied (charging) once a voltage is applied. However, once charging is complete, the current through the device is theoretically zero, even if voltage continues to be applied. Using the charging characteristics of the capacitor in this way, it is possible to detect the transient immediately.

As described in detail above, the power drop detection circuit of the present invention can prevent the power device from being damaged in the event of transient occurrence due to a power drop through an induction heating circuit through a capacitor capable of detecting a transient current.

In addition, by mounting the power drop detection circuit to the induction heating cooker it is possible to safely use the induction heating cooker in the event of a transient caused by the power drop.

Claims (4)

A circuit capable of detecting a power drop, the circuit comprising: a rectifier diode for rectifying an AC power source; A smoothing circuit unit having one end connected to the rectifying diode to smooth the rectified power; A resonant circuit part and a power drop detector connected at one end to the other end of the smooth circuit part; One end is connected to the other end of the power drop detection unit includes an abnormal state holding unit for outputting and maintaining a high (HI) value when a voltage value of more than the reference voltage value (VREF) is input from the power drop detection unit, And the power drop detecting unit detects a power drop by conducting a transient current to a capacitor having one end connected to the smoothing circuit unit when a transient current occurs due to a power drop. The power drop detection circuit of claim 1, wherein the capacitor is connected in series with one or more current path resistors. The power drop detection circuit according to claim 2, further comprising a discharge diode connected in parallel to the current path resistance to perform a discharge passage function during discharge of the capacitor. An induction heating cooker comprising a power drop detection circuit according to any one of claims 1 to 3 as an induction heating cooker.