EP0026033A1
Expired / Lapsed
EP
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D.C. power supply
Assignee: Hitachi Ltd
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Filing: 1980-07-28
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Granted: —
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Expires: 2000-07-28
Abstract
Abstract A D.C. power supply for use in microwave ovens has a main circuit (100) and a control unit (200). In the main circuit (100) an A.C. mains voltage is rectified by a rectification circuit (120) and then is chopped at at high frequency by means of a switching element (112). The resultant voltage is smoothed by a capacitor (119) before applied to a magnetron (130). The control unit (200) functions to control an ON-OFF operation of the switching element (112), and includes four control circuits (240,220,260 and 280). The first control circuit (240) functions to vary the duty ratio of the control pulse in accordance with the rectified voltage level and the current flowing through switching element (112). The second control circuit (220) limits the period of time during which the switching element performs an ON-OFF operation in accordance with the level of the rectified voltage. The third and fourth control circuits (260, 280) are protective against excess currents and voltages respectively to prevent damage to the switching element and magnetron. By this circuit configuration, the magnetron (130) ,of the microwave oven is supplied with a continuously controllable D.C. voltage of a flat waveform.
Inventors
- 👤 Hiroshi Fukui
- 👤 Amano Hisao
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-30 14:04
CPC Classifications
H; H02; H02M; H02M1/00; H02M1/40; H02M3/00; H02M3/02; H02M3/04; H02M3/10; H02M3/125; H02M3/135; H02M3/137
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
222 words
A D.C. power supply comprising a main circuit (100) including: a voltage source (101) for generating an A.C. voltage having a predetermined first frequency, a rectifier circuit (120) for converting said A.C. voltage into a D.C. voltage, and a switching element (112) having an anode, a cathode and a control electrode for chopping 'said D.C. voltage at a predetermined second frequency higher than said first frequency in response to a control pulse applied to said control electrode; a transformer (110) having a primary winding (110a) and a secondary winding(110b), said primary winding being connected to the switching element (112), such that a chopped current flows in one direction therethrough; characterized in that there is provided a control unit (200) including: a first control circuit (240) for controlling ON-OFF operation of the switching element of said main circuit, said control circuit comprising first means (107, 108) for sensing a level of said D.C. voltage, second means (243) for generating a pulse signal having said second frequency and third means (241) for controlling a duty ratio of said pulse signal in response to the output of the first means (107, 108) in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, said pulse signal being applied to the control electrode of said switching element (112).
Claim 2
Dependent Claim
222 words
A D.C. power supply comprising a main circuit (100) including: a voltage source (101) for generating an A.C. voltage having a predetermined first frequency, a rectifier circuit (120) for converting said A.C. voltage into a D.C. voltage, and a switching element (112) having an anode, a cathode and a control electrode for chopping 'said D.C. voltage at a predetermined second frequency higher than said first frequency in response to a control pulse applied to said control electrode; a transformer (110) having a primary winding (110a) and a secondary winding(110b), said primary winding being connected to the switching element (112), such that a chopped current flows in one direction therethrough; characterized in that there is provided a control unit (200) including: a first control circuit (240) for controlling ON-OFF operation of the switching element of said main circuit, said control circuit comprising first means (107, 108) for sensing a level of said D.C. voltage, second means (243) for generating a pulse signal having said second frequency and third means (241) for controlling a duty ratio of said pulse signal in response to the output of the first means (107, 108) in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, said pulse signal being applied to the control electrode of said switching element (112).
Claim 3
Dependent Claim
60 words
A D.C. power supply according to Claim 1, characterized in that said first control circuit (240) further comprises fourth means (VR 1 ) for producing a variable voltage to be applied to said third means (241) ·so that the duty ratio of said pulse signal can be controlled by the variable voltage in addition to the sensed D.C. voltage level.
Claim 4
Dependent Claim
72 words
A D.C. power supply according to Claim 1, characterized in that said first control circuit (240) further comprises fifth means (VR 3 ) for generating a predetermined constant voltage and means (D 2 ) for applying the constant voltage in place of the output of the third means when the constant voltage becomes greater than the output of the first means, so that the duty ratio of the pulse signal becomes constant.
Claim 5
Dependent Claim
105 words
A D.C. power supply according to Claim 1, characterized in that the first control circuit (240) further comprises means (109) for detecting a current flow passing through the main circuit, means (242) for producing a voltage corresponding to the detected current flow and means (D 3 ) for applying the voltage corresponding to the detected current flow in place of the output of the third means when the voltage corresponding to the detected current flow becomes greater than the output of the first means, so that the duty ratio of the pulse signal may vary in accordance with the current flow of the main circuit.
Claim 6
Dependent Claim
109 words
A D.C. power supply according to Claim 1, characterized in that the control unit (200) further comprises a second control circuit (220) including means (222) for producing a predetermined constant voltage, means (221) for comparing the sensed D.C. voltage obtained by the first means (107, 108) with the constant voltage to produce an output when the sensed D.C. voltage exceeds the constant voltage and gate means (301) connected to receive outputs of the comparison means (221) and the first control circuit (240), for inhibiting the application of the output of the first control circuit to the switching element (112) in response to the output of the comparison means (221).
Claim 7
Dependent Claim
120 words
A D.C. power supply according to Claim 1, characterized in that the control unit (200) further comprises a third control circuit (260) including means (262) for producing a predetermined constant current, means (109) for detecting a current flow passing through the main circuit (100), means (261) for comparing the detected current with the predetermined constant current to generate an output when the detected current becomes greater in level than the predetermined constant current, and gate means (301) connected to receive the outputs of the comparison means (261) and the first control circuit (240), for inhibiting the application of the output of .the first control circuit to the switching element (112) in response to the output of the comparison means (261).
Claim 8
Dependent Claim
121 words
A D.C. power supply according to Claim 1, characterized in that the control unit (200) further comprises a fourth control circuit (280) including means (281) for detecting a voltage developed across the primary winding of the transformer (110) or a voltage across the switching element (112), means (283) for producing a predetermined voltage, means (282) for comparing the detected voltage with the predetermined voltage to produce an output when one becomes greater than the other and gate means (301) connected to receive outputs of the comparison means (282) and the first control circuit (240), for inhibiting the application of the output of the first control circuit to the switching element (112) in response to the output of the comparison means (282).
Claim 9
Dependent Claim
39 words
A D.C. power supply according to any one of the preceding claims, characterized in that the rectifier circuit comprises a diode bridge having two branches, each branch comprising a diode (104 or 105) and a thyristor (132 or 133).
Claim 10
Dependent Claim
41 words
A D.C. power supply according to any one of the preceding claims, characterized in that a ,capacitor (106) is connected across the rectifier circuit (120), said capacitor having a value of capacitance which exhibits a low impedance at the second frequency.
Claim 11
Dependent Claim
24 words
A D.C. power supply according to any one of the preceding claims, characterized in that the switching element comprises a gate turn-off thyristor (112).
Claim 12
Dependent Claim
69 words
A D.C. power supply according to any one of the preceding claims, characterized in that the transformer (110) comprises a magnetic core (110c) defining a magnetic path on which the primary winding (110a) and secondary winding (110b) are wound, said magnetic path (110c) including a permanent magnet (110d) to provide a predetermined magnetic bias with respect to magnetic flux due to a current flowing through the primary winding (110a).
References Cited (Backward Citations)
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