JPH02109291A - Induction heating device - Google Patents

Abstract

PURPOSE:To restrain noise by which another electric equipment is influenced by providing an input power control means for controlling input power by changing high frequency oscillation frequency in the width of switching element conduction time capable of assuring the current conduction time of diode. CONSTITUTION:There is provided an inverter circuit 2 to which a commercial power supply 1 is connected and a control circuit 3 controlling operation of the circuit 2. This circuit 2 is composed of a diode 10 connected parallely reversely to a switching element, a heating coil 9 connected serially to the element and resonance condensor 8. The circuit 3 has an input power control means for controlling the input power of the circuit 2 at ON time of the element, and the means changes the width of ON time of the element within a range where a current flows in the diode 10. It is thus possible to prevent generation of electric noise caused by a sharp and strong current upon ON time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an induction heating device equipped with input power adjustment means.

BACKGROUND ART In an induction heating device having an inverter circuit including a resonant circuit including a heating coil and a resonant capacitor, there are two methods for adjusting the amount of input power.

(1) A method in which the high-frequency oscillation frequency is varied by controlling the on-time of the switching elements in the inverter circuit. (2) A method in which the high-frequency oscillation frequency is fixed and heating and stop settings are set.
＼ Method for varying the constant time ratio Problems to be solved by the invention In the case of a method for varying the high-frequency oscillation frequency, as the input power is reduced, the current conduction time of the diode connected in antiparallel to the switching element r- becomes short and eventually reaches zero, causing a problem in that a large high-frequency current flows when the switching element is turned on, which becomes a noise source and adversely affects other electrical equipment such as radios. Also,
In the case of a method in which the heating and stopping time ratio is varied, a large input power is required to start and stop the heating, which has the problem of causing a flickering phenomenon in general household electric light lines.

In view of the above problems, the first object of the present invention is to suppress the influence of noise on other electrical equipment, and the second object is to make it possible to vary the amount of input power over a wide range.

Means for Solving the Problems In order to achieve the above-mentioned first object, the first technical means of the present invention is to provide switching element conduction that can ensure the current conduction time of the diode connected in anti-parallel to the switching element. This configuration includes a manual power adjustment means that adjusts the amount of input power by varying the high-frequency oscillation frequency over a time period.

In addition, in order to achieve the above second object, the second aspect of the present invention
This technical means shortens the on-time of the switching element at the minimum level 1 in which the current flows through the diode, and further reduces the on-time of the switching element when the input power adjustment range requires lower input power adjustment. The input power amount is adjusted by changing the set time ratio between heating and stopping, instead of changing the ON time of the switching element.

Effects According to the first technical means of the present invention, since the current conduction time of the diode is ensured, it is possible to prevent a steep and large current from flowing when the switching element is turned on. As a result, electrical noise generated by a steep and large current when turned on can be prevented.

In the second technical means, when the input power is reduced, the ON time of the switching element is shortened to the extent that the current conduction time of the diode can be secured (current flows through the diode). When the time reaches zero, the ON time of the switching element is fixed, and the average input power value is lowered by changing the heating and stopping time ratio, so it is necessary to set a wide range of settings to the low input power amount side. Can be done.

Embodiment Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings. In FIG. 1, 1 is a commercial power source, which is connected to an inverter circuit 2. In FIG. The inverter circuit 2 has a rectifier 5 for rectifying the commercial power supply, a choke filter 6, and a high frequency bypass capacitor 7, and furthermore, a parallel circuit of a heating coil 9 and a resonance capacitor 8 and a power transistor 11 are connected from a branch point a. 4, which has a configuration in which a diode 1o is connected in antiparallel to the transistor 11,
FIG. 2 shows waveforms of various parts of the one-inverter circuit 2 at maximum power. In addition, the voltage waveform between the emitter and the collector of the voltage vcKit l-transistor 11 in the figure. 2 shows a current waveform flowing between the collector and emitter of the transistor 11, and 2 shows a base current waveform flowing into the base of the transistor 110.

The control circuit 3 uses a human power detection circuit 31 to detect the amount of power input to the inverter circuit 2 by receiving a signal from the current transformer 4 from a terminal a. A setting circuit 33 sets a predetermined amount of power, a comparison circuit 32 determines the magnitude of the signal from the input detection circuit 31, and a timing circuit 34 determines the ON time of the transistor 11. That is, when the input power amount detected by the input detection circuit 31 is smaller than the power amount set by the setting circuit 33, the timing circuit 34 operates to increase the on time of the transistor 11. A signal is then transmitted from the timing circuit 34 to the drive circuit 36, and the drive circuit 36 is supplied with a base current from the end fb to drive the transistor 11. In other words, when reducing the human power by varying the frequency, it is sufficient to shorten the forward drive time tB.As the input power decreases, the diode 1o becomes conductive as shown in Fig. 3.
- The passing time td also decreases and eventually becomes zero.

Let 13 hours at that time be t and o. If the waiting time tB is set to tB<tBo in order to further reduce the input power, the waveform shown in FIG. 4 will be obtained. That is V. 8 Voltage does not become zero and voltage V. When transistor 11 is turned on with The waveform is a steep current i because the discharge current of the resonance capacitor 8 flows. is generated, which becomes a source of high-frequency noise. On the other hand, the conduction time (t, i
) is detected by the t,1 detection circuit 36, and when (ta)≧0, the control is performed as described above, but (td)
(When it becomes O, a limit is added by the timing circuit 34 so that the ON time of the transistor 11 can be maintained to maintain the state of td=o. Next, the input power amount is set lower than the input power amount determined by t6=o. The configuration for this case is shown in Fig. 6.The td detection circuit 36 detects the diode conduction time td using the voltage between the terminals of the diode 10 from the terminal C.
At the time t6=O, a limit is placed on the timing circuit 34 so that the on-time of the transistor 11 does not become any shorter. Nevertheless, if the input electric energy set by the setting circuit 33 is smaller than the human power electric energy detected by the input detection circuit 31, the duty circuit 37 inputs the average human power electric energy as the set input according to the output of the comparison circuit 32. The duty ratio for operating and stopping the transistor 11 is set to match the amount of electric power. In other words, the setting input power amount, detection input power amount, and de.

The tee ratio is as shown in the example table below 3,■
B (Effects of the Invention According to the description of the embodiments above, the present invention exhibits the following effects.

9. (1) Detect the diode conduction time (td) and check if td≧O
By adjusting the input power amount within a certain range and controlling the input power amount so that it does not decrease any further when td=o, the steep current that occurs when the power transistor in the inverter circuit is turned on can be prevented from flowing. This can prevent unnecessary high-frequency noise and reduce noise interference with other equipment.

(2) When it is necessary to set a low input power below the input power corresponding to the diode conduction time t4-o, high frequency noise can be reduced by automatically switching to duty control under control such that td=O. Low input power regulation with less flicker disturbance may be possible.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an induction heating device showing an embodiment of the present invention, Fig. 2 is an operating waveform diagram of each part, and Fig. 3 shows the correlation between input power amount and diode conduction time with respect to transistor forward drive time. FIG. 4 is a waveform diagram of various parts when the diode is non-conducting, and FIG. 6 is a block diagram of an induction heating apparatus showing another embodiment of the present invention. 2. Inverter circuit, 3. Control circuit, 8 resonant capacitor, 9. Heating coil, 10. Diode,
11...Scream/Rangista. Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (2)

[Claims] (1) Equipped with an inverter circuit that converts DC power into high-frequency power, and a control circuit that controls the operation of this inverter circuit, the inverter circuit includes a diode connected in antiparallel to a switching element, and a diode connected in series to the switching element. and a resonant capacitor forming a resonant circuit with the heating coil, the control circuit having input power adjusting means for adjusting the input power of the inverter circuit according to the on time of the switching element, The induction heating device is characterized in that the input power adjusting means varies the on-time width of the switching element within a range in which current flows through the diode. (2) When the input power adjustment means determines the ON time of the switching element based on the set input power value, it detects whether or not current is flowing through the diode during the ON time, and determines whether current is flowing through the diode. In this case, the ON time is gradually increased until current flows through the diode, and the heating and stopping operations are performed intermittently using the input power at that time until the average input power matches the initially set input power value. The induction heating device according to claim 1, wherein the induction heating device is controlled according to a time ratio.