JP2712582B2 - Induction heating cooker - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an induction heating cooker.

2. Description of the Related Art Conventionally, this type of induction heating cooker has a configuration as shown in FIG.
The power control volume knob of the induction heating cooker corresponding to the input setting unit 114 has a circuit configuration as shown in FIG.
The waveform of each part of the RWM circuit 113 is as shown in FIG.
The relationship between the slide position of the power control volume knob 119 of the input setting unit 114 and the input power is shown in FIG.
It looked like Figure 0.

That is, the switching element 1 in the inverter circuit 108
In the drive 05, the output of the reference voltage setting circuit 112 which rises and falls in proportion to the triangular wave which is the output (z) of the RC charge / discharge circuit 111 in the PWM circuit 113 and the sliding position of the power control volume knob 119 of the input setting unit 114 y) is compared with the comparison circuit 110, and the output (z) of the RC charging / discharging circuit 111 is compared with the reference voltage setting circuit 1
An on-pulse is generated only during a period lower than the output (y) of the circuit 12 and the output (z) of the RC charge / discharge circuit 111 is generated.
The waveform of the triangular wave was as shown in FIG. 7b.

However, in such an RC charging / discharging circuit having a triangular wave output, in the case of an induction heating cooker having a half-bridge inverter circuit, the sliding position of the power control volume knob 119 is slightly smaller than the strong input setting. There is a problem that the input power may be larger in the input setting.

That is, in the case of an induction heating cooker having a half-bridge inverter circuit, the input power has a maximum value when the on-pulse width of the switching element 107 of the half-bridge inverter circuit 108 is 1/2 of the oscillation cycle, and the on-pulse width is equal to the oscillation cycle. If the input power is larger than 1/2, the input power will be smaller.
When the slide position of 119 is set to the strong setting, even if the on-pulse width of the switching element 107 determined by the output z of the RC charge / discharge circuit 111 and the output y of the reference voltage setting circuit 112 is set to 1/2 of the oscillation cycle, When the on-pulse width of the switching element shifts by more than half of the oscillation cycle due to the variation of the output z of the RC charge / discharge circuit 111 and the variation of the output y of the reference voltage setting circuit 112, and the on-pulse width varies in a wider direction,
The above problem occurs.

Therefore, according to the present invention, even if the output of the reference voltage setting circuit varies, the pulse width of the on-pulse signal of the switching element at the time of the strong input setting is maintained at 1/2 of the oscillation cycle, and the slide position of the power control volume knob is shifted to the strong setting side. It is an object of the present invention to prevent a decrease in the input power when it is moved.

Means for Solving the Problems And in order to achieve the above object, the present invention provides an R circuit in which the maximum pulse width of the ON pulse of the drive of the switching element, which is the output of the PWM circuit, is not more than 1/2 of the oscillation period.
It deforms the waveform of the triangular wave that is the output of the C charge / discharge circuit.

The operation of the induction heating cooker according to the present invention is such that the output of the reference voltage setting circuit which rises and falls in proportion to the slide position of the power control volume knob, which is the input setting means, is higher than a design value when the power control volume knob is set to a high level. Even if it fluctuates higher, the waveform of the triangular wave that is the output of the RC charge / discharge circuit acts to keep the maximum pulse width of the ON pulse of the drive of the switching element of the inverter circuit constant at 1/2 of the oscillation cycle, The on-pulse width does not become more than 1/2 of the oscillation period. As a result, the inconvenience of increasing the input power with a setting smaller than the strong setting of the power control volume knob is eliminated.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

1 to 3, reference numeral 1 denotes a DC power supply, 8 denotes a half-bridge inverter circuit including a resonance capacitor 2, a heating coil 3, diodes 4, 5 and switching elements 6, 7, and 9 denotes switching elements 6 and 7. A drive circuit 13 drives the switching elements 6 and 7, and a PWM circuit 13 determines the ON pulse width of each drive.
Is the slide position of the RC charge / discharge circuit 11 having an output obtained by deforming the waveform of a triangular wave so that the on-pulse width of the drive of the switching element 7 does not become 1/2 or more of the oscillation cycle, and the power control volume knob 19 of the input setting unit 14 The reference voltage setting circuit 12 having a reference voltage output that rises and falls in proportion to the output of the RC charge / discharge circuit 11
When the output of the charging / discharging circuit 11 is smaller than the output of the reference voltage setting circuit 12, an on-pulse signal of the switching element 7 is generated. ing.

The circuit configuration of the main part of the RC charge / discharge circuit 11 and the waveform of each part will be described. A charge / discharge circuit composed of a resistor 15, a capacitor 17, and a transistor 16 is controlled by an input a which is the base of the transistor 16, and
When the output c becomes low due to turning on of 16
A terminal b for rapidly charging the capacitor 17 after a time period of / 2 is connected to the output c via the diode 18. Due to this terminal b, the output c of the RC charging / discharging circuit 11 becomes high instantaneously after half the oscillation period from the moment when the transistor 16 is turned on and the output c becomes low. The triangle wave is transformed as shown in FIG.

FIG. 3 shows a state of the power control volume knob 19 of the input setting unit 14.
Is slid from weak to strong, the output d of the reference voltage setting circuit 12 increases in proportion to the sliding position. For convenience of explanation, the slide position of the power control volume knob 19 is defined as shown in FIG.

Next, the operation of this embodiment will be described with reference to FIGS.

Now, the output c of the RC charging / discharging circuit 11 is as shown at 20 in FIG.
When the output of the reference voltage setting circuit 12 is in a state like 21 when is set to a strong position, the ON signal of the drive of the switching element 7 becomes 1/2 of the oscillation period as 23 and the input The relationship between the slide position of the power control volume knob 19 of the setting unit 14 and the input power is as shown by the solid line 24 in FIG.

Next, even when the output of the reference voltage setting circuit 12 when the power control volume knob 19 of the input setting unit 14 is set to the high setting fluctuates to a higher value as indicated by 22 (dotted line), the output c of the RC charge / discharge circuit 11
Is high instantaneously after half the oscillation period from the moment output c goes low as in waveform 20, so RC
The ON signal of the drive of the switching element 7 determined by the output 20 of the charging / discharging circuit 11 and the output 22 of the reference voltage setting circuit 12 is output when the output of the reference voltage setting circuit 12 does not vary like 23 (reference voltage setting). (When the output d of the circuit 12 is 21)
Similarly to the above, the oscillation period becomes 1/2, and the relationship between the sliding position of the power control volume knob 19 of the input setting unit 14 and the input power is as shown by 25 (dotted line) in FIG. As a result, the input power at the time of the strong input setting does not become smaller than the input power at the time of the slightly smaller input setting due to the strong input setting.

Effect of the Invention As described above, the present invention provides a method for controlling the switching element drive, which is the output of the PWM circuit, so that the maximum pulse width of the on-pulse signal does not become more than 1/2 of the oscillation cycle.
Since the waveform of the triangular wave output from the RC charge / discharge circuit is modified, it is possible to eliminate the inconvenience of increasing the input power with a setting smaller than the strong setting of the power control volume knob.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit block diagram of an induction heating cooker according to the present invention, and FIGS. 2a and 2b are schematic circuit diagrams of an RC charge / discharge circuit of the induction heating cooker and waveforms of respective parts thereof. Fig. 3, Fig. 3 is a front view around the power control volume knob of the induction heating cooker, Fig. 4 is an operation waveform diagram of a PWM circuit of the induction heating cooker, and Fig. 5 is a power control volume of the induction heating cooker. FIG. 6 is a schematic circuit block diagram of a conventional induction heating cooker, and FIGS. 7a and 7b are schematic circuit diagrams of an RC charging / discharging circuit of the induction heating cooker and respective parts thereof. Fig. 8 is a front view around the power control volume knob of the induction heating cooker, and Fig. 9 is the PWM of the induction heating cooker.
FIG. 10 is an operation waveform diagram of the circuit, and FIG. 10 is a graph of input power with respect to a sliding position of a power control volume knob of the induction heating cooker. 8 ... Inverter circuit, 7 ... Switching element, 11 ...
… RC charge / discharge circuit, 12… Reference voltage setting circuit, 10… Comparison circuit, 20… A waveform modified from a triangular wave.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hirofumi Noma 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-61-148795 (JP, A) JP-A-63- 119189 (JP, A) JP-A-2-269476 (JP, A)

Claims (1)

(57) [Claims] An RC charging / discharging circuit for determining an on-pulse width of a drive of a switching element of an inverter circuit, a reference voltage setting circuit, and a comparing circuit for comparing an output of the RC charging / discharging circuit with an output of the reference voltage setting circuit. In the PWM circuit, the maximum pulse width of the ON pulse of the drive of the switching element, which is the output of the PWM circuit, is equal to the oscillation period.
An induction heating cooker, wherein a waveform of a triangular wave which is an output voltage of the RC charge / discharge circuit is modified so as not to be 1/2 or more.