Induction heating cooker with constant frequency controlled inverter

• US 5,319,174 A
• Filed: 08/28/1990
• Issued: 06/07/1994
• Est. Priority Date: 06/07/1990
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Iwai, Toshiaki, Noma, Hirofumi, Kominami, Hideyuki, Omori, Hideki, Asada, Kazuhiko
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US07/573,407
• Time in Patent Office: 1,379 Days
• Field of Search: 219/10.77, 219/10.493, 363/96, 363/97, 363/131, 363/132, 363/98
• US Class Current: 219/664
• CPC Class Codes: H02M 7/53803 with automatic control of output voltage or current
• CPC Class Codes: H05B 6/065 using coordinated control of multiple induction coils
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

An induction heating cooker has a rectifier (13) for producing pulsating DC current, an inverter (14) which receives the pulsating current given from the rectifier (13) and produces a high frequency output current and a load circuit (15) including an output coil (21) and a resonance capacitor (22) connected in series to each other to receive high frequency output signal from the inverter, and the variation or adjustment of output electromagnetic power is made by changing duty ratio of the high frequency output current of the inverter by giving variable duty ratio setting signals to switching elements (Qa, Qb) in the inverter 14; the frequency of the high frequency output current of the inverter 14 is fixed, and therefore, unpleasant interference sound is not generated at parallel simultaneous operation.

Claims

1. An induction heating cooker comprising:

a rectifier for producing a DC current by rectifying an AC current,

an inverter having first and second switching elements, connected in series across output terminals of said rectifier,

a variable duty ratio oscillator for generating square wave signals which are constant in frequency but variable in duty ratio and applying said signals to alternately drive said first and second switching elements to turn on said switching elements in a manner such that said switching elements are alternately rendered conductive in a complementary manner such that said first and second simultaneous switching elements are not both conductive or both non-conductive at the same time, to thereby produce an output inverter signal, wherein said variable duty ratio oscillator comprises a variable range limiter for limiting a duty ratio of said variable duty ratio oscillator to one of a range, selected from a range of duty ratios from zero to 1/2 and a range of duty ratios from 1/2 to 1,

duty ratio setting means for setting a duty ratio of said square wave signal, said duty ratio setting means comprising a physical amount detector for detecting a physical amount which has a correlation with one of input power of said induction heating cooker or with current of said at least two switching elements and a differential amplifier which compares an output of said physical amount detector with a predetermined reference value, and

a load circuit having an output coil and a resonant capacitor, coupled to receive said output inverter signal.

2. An induction heating cooker comprising:

a rectifier for producing a DC current by rectifying an AC current,

an inverter having first and second switching elements, connected in series across output terminals of said rectifier,

a variable duty ratio oscillator for generating square wave signals which are constant in frequency but variable in duty ratio and applying said signals to alternately drive said first and second switching elements in a manner such that said switching elements are alternately rendered conductive in a complementary manner such that said first and second simultaneous switching elements are not both conductive or both non-conductive at the same time to thereby produce an output inverter signal, said variable duty ratio oscillator producing a duty ratio proportional to an input voltage thereto,

duty ratio setting means for setting a duty ratio of said square wave signal, and

a load circuit having an output coil and a resonant capacitor, coupled to receive said output inverter signal, said duty ratio setting means including means for receiving a parameter indicative of an output electromagnetic power of the cooker, means for comparing said parameter with a reference, and means for outputting a voltage indicative of a difference between said parameter and said reference and applying it as said input voltage to said variable duty ratio oscillator.

3. An induction heating cooker as in claim 2 wherein said variable duty ratio oscillator includes means for using said input voltage to charge a capacitor, and means for producing a square wave output signal having a duty cycle depending on how much said capacitor charges within a fixed period.