JPS63250086A - Induction heating cooker - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention connects an inverter circuit consisting of a capacitor, a heating coil, a switching element, etc. to a DC power source, and drives the switching element of the inverter circuit at high frequency. This invention relates to an induction heating cooker that heats a pot or the like by passing a high-frequency current through a heating coil, and is particularly intended to provide an improvement measure for power supply voltage fluctuations when detecting a small load.

[Prior art]

A conventional induction heating cooker has a structure as shown in FIG. That is, 1 is a commercial power supply, 2 is a rectifier stack connected to the commercial power supply I, 3 is a smoothing capacitor,
4 is a heating coil whose energization is controlled by on/off control of the switching element 5; 6 is a resonance capacitor connected in parallel to the heating coil 4;

The resonance capacitor 6, the heating coil 4, and the switching element 5 constitute a well-known inverter circuit, and by driving the inverter circuit in full oscillation, a high-frequency alternating current is passed through the heating coil 4, and the magnetic field generated at this time causes tingling in the metal pot. A current is generated, which heats the steel.

7 is a drive circuit for controlling the switching element 5 on and off based on the control signal from the control circuit 8;
The induction heating output is adjusted depending on the length of time the switching element 50 is on. Adjustment of this heating output is performed by varying the control volume 9. When the volume 9 is varied, the control signal width (drive pulse width) output from the control circuit 8 is varied, and as a result, the ON time of the switching element 50 is varied. It will be controlled.

Reference numeral 10 denotes a current transformer for detecting current changes on the AC power supply 1 side, and is connected to the control circuit 8 and the load detection circuit 1 side. The load detection circuit 11 is connected to the heating coil 4.
This detects whether the second load is appropriate or not, and when the load is a small item or no load, a High signal is output when the LOW% load is appropriate.

12 is a start/stop circuit that outputs a signal V3 that drives the switching element 5 to full oscillation at predetermined time intervals, that is, intermittently, when the signal from the load detection circuit 11 is OW; The signal from 11 is H4g
11 (when the load is appropriate), the output V3 is always high.

The start/stop circuit 12 will be explained below based on FIG. 5. 13 is a comparator, its ■ terminal is connected to the output terminal from the load detection circuit 11 via a resistor 14, and its ○ terminal is connected via a capacitor 15 to a DC voltage Vc.
is applied.

16, +7, 18, and 19 are resistors, and 20 is a diode.

Now, assuming that the output from the load detection circuit 11 is Low, the voltage divided by the resistor 16.17 is applied to the ■ terminal of the comparator 13, and the capacitor 15 is connected to the ○ terminal. From the relationship, the capacitor 15
C, from the output terminal of the comparator 13 depending on the charging and discharging of
A High+Low signal V3 (search pulse) is output at intervals determined by the R constant.

When a load such as a pot is placed on the heating coil 4 and the load is suitable, the output from the load detection circuit 1 becomes High, regardless of whether the capacitor 15 is charged or discharged. A high signal is always output from the comparator 13, and as a result, normal induction heating operation is performed.

[Problem that the invention seeks to solve]

However, with the structure described above, if an unsuitable small object load is left in place for a long time when the search pulse V3 is oscillated, the small object load may be heated even if it is intermittently. Since the cycle is carried out at predetermined fixed time intervals, even if the power supply voltage is high, heating will occur with the same on-duty, which has the disadvantage that the temperature of the small load becomes abnormally high. .

[Means for solving problems]

As shown in FIGS. 1 and 2, the present invention connects an inverter circuit consisting of a capacitor, a heating coil, a switching element, etc. to a DC power source, and drives the switching element of the inverter circuit at a high frequency to generate a high frequency signal in the heating coil. A load detection circuit that conducts current to heat a pot, etc., and detects whether or not the load is suitable, and a switching element that switches on the switching element when the load detection circuit detects that the load is inappropriate. In an induction heating cooker equipped with a start/stop circuit that outputs a signal for intermittently oscillating drive, means for comparing an output signal from the load detection circuit with a signal from a secondary coil provided near the heating coil. By comparing , the on-duty ratio of the intermittent oscillation output of the start/stop circuit is made inversely proportional to the power supply voltage.

[For production]

According to the present invention, the period during which the comparator outputs a High signal depends on the charging time of the capacitor connected to the ○ side terminal of the comparator. Since the voltage is obtained from the next coil, if the power supply voltage rises, charging of the capacitor will start 9 earlier, and the high output time from the comparator will be shortened accordingly. In other words, the on-duty ratio of the intermittent oscillation output of the start/stop circuit is inversely proportional to the power supply voltage, and even if the power supply voltage fluctuates when a search pulse is generated (when the start/stop circuit's intermittent oscillation is applied), the small load will be abnormal. [Example] The present invention is roughly the same as that shown in FIG.
The same parts as before are indicated by the same symbols.

What is different from the conventional system in FIG. 2 is that a secondary coil 21 is provided near the heating coil 4, and a signal from the secondary coil 2I is input to a start/stop circuit 22.

As shown in FIG. 1, in the start/stop circuit 22, the output terminal of the load detection circuit 11 is connected to the ■ terminal of the comparator 23 via a resistor 24, and the diode 25 is connected to the e terminal of the start/stop circuit 22.
1 and is connected to the secondary coil 21 through a series circuit consisting of a resistor 26 and a resistor 26. Further, a capacitor 2 constituting a time constant circuit is connected between the ○ terminal of the comparator 23 and the diode 25.
7 and a resistor 28 are connected. 29.30 is resistance, V
c is a DC voltage, and V3 is an output signal of the comparator 23.

Now, if there is no load on the heating coil 4'' or even if there is a small load, the output from the load detection circuit 11 is LO.
With W, the DC voltage Vc is applied to the comparator 23 via the resistor 29.
Since the voltage is applied to the ■ terminal of the comparator 23, the output v3 of the comparator 23 is
is High, and the switching element 5 is turned on.

The on-time of the switching element 5 at this time is controlled by the control circuit 8 so that it is minimized (weak heating).

Thus, the switching element 5 is energized, and the heating coil 4
When a current flows through and a magnetic field is generated, this magnetic field causes 2
A current is generated in the next coil 21, and the resistor 26 and diode 2
The capacitor 27 is charged via the capacitor 5. When the voltage v1 on the O terminal side and the voltage V2 on the ■ terminal side of the comparator 23 reach the same level by charging the capacitor 27, the output V3 of the comparator 23 becomes Low, and the switching element 5 is no longer energized. Stop.

Thereafter, when the capacitor 27 is discharged through the resistor 28, v2>v again, a high signal is output from v3, and the switching element 5 is energized. Thereafter, this operation is repeated.

On the other hand, if the pot placed on the heating coil 4 has an appropriate load, the output from the load detection circuit 11 will be High, and V2:>Vl will always be maintained, and the output v3 of the comparator 23 will always be HighbL. Then, normal heating operation is performed.

Now, if an unsuitable load is placed on the heating coil 4, the comparator 23 intermittently outputs Hlgh as described above.
, a Low signal is repeatedly output nine times, but the comparator 2
The Higb or Low signal of the output V3 of No. 3 depends on the time required for charging and discharging the capacitor 27. On the other hand, the discharging time of the capacitor 27 is fixed because it is determined by its time constant, whereas the charging time is proportional to the voltage.

Therefore, according to the present invention, when the power supply voltage fluctuates, the on-duty ratio of the comparator 23 is inversely proportional to the power supply voltage9. It is possible to prevent abnormal temperature rises when small objects are loaded due to voltage fluctuations.

〔effect〕

Since the present invention is constructed as described above, even if the power supply voltage increases when detecting a small load, the on-duty ratio becomes small, so that the small load does not generate abnormal heat as in the conventional case, and is very effective. This can have the remarkable effect of making it safer.

[Brief explanation of drawings]

Fig. 1 is an electric circuit diagram of the start/stop circuit used in the induction heating cooker of the present invention, Fig. 2 is a schematic configuration diagram of the same induction heating cooker, Fig. 3 is the time chart of Fig. 1, and Fig. 4 is A comparative characteristic diagram of the on-duty ratio of the power supply voltage -V3 of the present invention and the conventional one, and FIG. 5 shows an electric circuit diagram of the conventional start/stop circuit. 4: Heating coil, 5 Niswitching element, 6: Capacitor, II: Load detection circuit, 21: Secondary coil, 22: Start/stop circuit, 23: Comparator, 27: Capacitor, 28:
resistance. Agent Patent attorney Takeshi Sugiyama (and 1 other person) Figure 3 `` `` ``''' 9 squares (Tn No. 4)
Figure 5

Claims (1)

[Claims] 1. An inverter circuit consisting of a capacitor, a heating coil, a switching element, etc. is connected to a DC power source, and the switching element of the inverter circuit is driven at high frequency to flow a high-frequency current to the heating coil to heat a pot, etc. and a load detection circuit that detects whether the load is suitable or not, and a start/stop circuit that outputs a signal that intermittently drives the switching element to oscillate when the load detection circuit detects that the load is inappropriate. In an induction heating cooker equipped with a circuit, intermittent oscillation of the start/stop circuit is performed by comparing the output signal from the load detection circuit and the signal from the secondary coil provided near the heating coil using a comparing means. An induction heating cooker characterized by making the output on-duty ratio inversely proportional to the power supply voltage.