Electric heating – Metal heating – Of cylinders
Patent
1983-07-05
1985-11-26
Envall, Jr., Roy N.
Electric heating
Metal heating
Of cylinders
219 1049R, H05B 606, H05B 664
Patent
active
045556083
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a bridge inverter for use in induction heating apparatuses having large load variations, particularly induction heating cooking appliances.
2. Description of the Prior Art
Generally, in an inverter device for induction heating cooking appliances, since the load is in the form of a pan, stabilized operation is required irrespective of the material of the pan and irrespective of the presence or absence of a pan. Further, as is known in the art, a bridge inverter comprises a plurality of series-connected switching elements connected to a power source, the output from said converter being obtained at the junction of the series connection, said switching elements being alternately or successively driven. This inverter, however, has drawbacks; for example, when the switching time of the elements is prolonged by a temperature increase or when there is a large variation in the load, there is the danger of the switching elements being simultaneously rendered conductive and thereby damaged. As a solution to this problem, the common means is to provide a fixed dwell period for stopping all the switching elements at the drive signal switching time in consideration of the amount of variation when the switching time varies. This means, however, does not essentially eliminate the danger of simultaneous conduction, and the provision of a sufficient dwell period has been the major cause of reduction of the operating efficiency of the inverter device. On the other hand, when an erroneous input signal is transferred to the control circuit, this is very undesirable since it leads to the simultaneous conduction of the switching elements of the inverter device or to abnormal oscillation thereof if the signal is on the level of not damaging the elements. As a solution of this problem, the common means is to stabilize the circuit by using a capacitor or the like which bypasses erroneous input signals. This means, however, depends on the correlation between the capacitance of the capacitor and the magnitude of the erroneous input signal, and can hardly serve as a radical solution to the problem.
SUMMARY OF INVENTION
The present invention provides an inverter device which operates in an efficient and stable manner, rarely malfunctioning, despite variations in load and in the parameters of the switching elements of the inverter device. Thus, it provides a bridge inverter device which functions on the principle of detecting the complete turn-off of one of two switching elements by detecting rising and falling voltage signals and then driving the other of the two switching element. Concerning erroneous input signals, during driving of either switching element, any input signal from the inverter is inhibited to ensure that there is essentially no simultaneous conduction taking place even if there is a variation in the characteristics of the switching elements or an initial variation. Furthermore, the inverter device is highly stable against malfunction and abnormal oscillation.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram showing an inverter device for induction heating according to an embodiment of the invention;
FIG. 2 is a waveform diagram showing the operation of FIGS. 1 and 3; and
FIG. 3 is an electric circuit diagram showing a concrete electric circuit for the device.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The arrangement will be described with reference to FIG. 1. The numeral 1 denotes a commercial AC voltage source; numeral 2 denotes a full-wave rectifier; numeral 3 denotes a filter capacitor, these parts constituting a rectifier circuit. The numerals 4 and 5 denote resonance capacitors, and 6 and numerals 7 denote switching elements, which are transistors in this embodiment and will be hereinafter referred to as transistors. The numerals 8 and 9 denote diodes connected across said transistors 6 and 7, respectively. The numeral 10 denotes an induction heating and 11 denotes a cooking pan, these parts constituting a bridge inver
REFERENCES:
patent: 3898410 (1975-08-01), Peters, Jr.
patent: 4115677 (1978-09-01), Yamamura et al.
Mizukawa Takumi
Ogino Yoshio
Ohmori Hideki
Sato Taketoshi
Envall Jr. Roy N.
Lateef Marvin M.
Matsushita Electric - Industrial Co., Ltd.
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