D.C. Power supply

• US 4,319,317 A
• Filed: 07/17/1980
• Issued: 03/09/1982
• Est. Priority Date: 08/22/1979
• Status: Expired due to Term

• Current Assignee: Hitachi Metals (Thailand) Ltd.
• Original Assignee: Hitachi, Ltd., Hitachi Metals (Thailand) Ltd.
• Inventors: Fukui, Hiroshi, Amano, Hisao
• Primary Examiner(s): Shoop, William M.
• Application Number:
  US06/169,770
• Time in Patent Office: 600 Days
• Field of Search: 219/10.55 B, 328/262, 328/263, 363/27, 363/28, 363/34, 363/37, 363/41, 363/79, 363/21, 363/124, 307/252 C
• US Class Current: 363/124
• CPC Class Codes: H02M 1/40 Means for preventing magnetic saturation
• CPC Class Codes: H02M 3/137 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A d.c. power supply for use in microwave ovens in which an a.c. voltage having a commercial frequency is rectified and then is chopped at a high frequency by means of a switching element. The resultant voltage is smoothed before being applied to the microwave oven. The voltage level of the commercial frequency voltage is sensed to produce a control pulse the duty ratio of which becomes greater as the voltage level becomes lower. The control pulse is used to control the ON-OFF operation of the switching element. By this circuit configuration, the microwave oven is supplied with a continuously-controllable d.c. voltage having a flat waveform.

Claims

1. A d.c. power supply comprising a main circuit and a control unit;

said main circuit including a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage; and

a switching element connected to said rectifier circuit and having an anode, a cathode and a control electrode for chopping said d.c. voltage at a predetermined constant second frequency higher than said first frequency in response to a control pulse applied to said control electrode; and

said control unit including a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit comprising first means for sensing the level of said d.c. voltage at an output terminal of said rectifier circuit, second means for generating a pulse signal having said constant second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, and means for applying said pulse signal to the control electrode of said switching element.

9. A d.c. power supply as defined in claim 1 or 2, wherein the rectifier circuit comprises a diode bridge including at least one thyristor.

11. A d.c. power supply as defined in claim 1 or 2, wherein the switching element comprises a gate turn-off thyristor.

21. A d.c. power supply as defined in claim 1 or 2, wherein said third means includes a flip-flop having a set terminal coupled to receive the output of said second means to produce a control pulse in response to a pulse from said second means, and said flip-flop further having a reset terminal coupled to the junction of a capacitor and the output of said first means to reset the flip-flop when the charge on the capacitor from the voltage level detected by said first means reaches a predetermined level.

2. A d.c. power supply having a main circuit and a control unit;

said main circuit comprising

a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage;

a switching element connected to said rectifier circuit and having an anode, a cathode and a control electrode for chopping said d.c. voltage at a predetermined constant second frequency higher than said first frequency in response to a control pulse applied to said control electrode;

a transformer having a primary winding and a secondary winding, said primary winding being connected to said switching element such that a chopped current flows in one direction therethrough; and

smoothing means connected to the secondary winding of said transformer to smooth the voltage developed thereacross;

said control unit comprising a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit including first means for sensing the level of said d.c. voltage at an output terminal of said rectifier circuit, second means for generating a pulse signal having said constant second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, and means for applying said pulse signal to the control electrode of said switching element.

3. A d.c. power supply as defined in claim 2, wherein said first control circuit further comprises fourth means for applying a selectively-variable voltage to said third means so that the duty ratio of said pulse signal is controlled on the basis of said variable voltage in addition to the sensed d.c. voltage level.

4. A d.c. power supply as defined in claim 2, wherein said first control circuit further comprises fifth means for generating a predetermined constant voltage and means for applying the constant voltage to said third means in place of the output of the first 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.

5. A d.c. power supply as defined in claim 2, wherein the first control circuit further comprises means for detecting the current flow through the main circuit, means for producing a voltage corresponding to the detected current flow and means for applying the voltage corresponding to the detected current flow to said third means in place of the output of said first means when the voltage corresponding to the detected current flow becomes greater than the output of said first means, so that the duty ratio of the pulse signal may vary in accordance with the current flow of the main circuit.

6. A d.c. power supply as defined in claim 2, wherein said control unit further comprises a second control circuit including means for producing a predetermined constant voltage, comparing means for comparing the sensed, d.c. voltage obtained by said first means with said predetermined constant voltage to produce an output when the sensed d.c. voltage is greater than said predetermined constant voltage, and gate means connected to receive outputs of said comparing means and said first control circuit for inhibiting the application of the output of the first control circuit to the control electrode of said switching element in response to the output of said comparing means.

7. A d.c. power supply as defined in claim 2, wherein said control unit further comprises a third control circuit including means for producing a predetermined constant current, detecting means for detecting the current flow passing through said main circuit, comparing means for comparing said detected current with said predetermined constant current to generate an output when the detected current becomes greater in level than the predetermined constant current, and gate means connected to receive the outputs of the comparing means and the first control circuit for inhibiting the application of the output of the first control circuit to the control electrode of said switching element in response to the output of the comparing means.

8. A d.c. power supply as defined in claim 2, wherein the control unit further comprises a fourth control circuit including detecting means for detecting the voltage developed across the primary winding of said transformer and a voltage across said switching element, means for producing a predetermined voltage, comparing means for comparing at least one of the detected voltages with said predetermined voltage to produce an output when one becomes greater than the other, and gate means connected to receive outputs of said comparing means and said first control circuit for inhibiting the application of the output of said first control circuit to the control electrode of said switching element in response to the output of said comparing means.

10. A d.c. power supply as defined in claim 2, wherein a condenser is connected across the rectifier circuit, said condenser being selected to have a value which exhibits a low impedance at said second frequency.

12. A d.c. power supply as defined in claim 2, wherein said transformer comprises a magnetic core defining a magnetic path on which the primary and secondary windings are wound, said magnetic path including a permanent magnet to provide a predetermined magnetic bias with respect to magnetic flux due to a current flowing through the primary winding.

13. A d.c. power supply comprising a main circuit and a control unit;

said main circuit including a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage; and

a switching element connected to said rectifier circuit and 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; and

said control unit including a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit comprising first means for sensing the level of said d.c. voltage, second means for generating a pulse signal having said second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, and means for applying said pulse signal to the control electrode of said switching element, wherein said first control circuit further comprises fourth means for applying a selectively-variable voltage to said third means so that the duty ratio of said pulse signal is controlled on the basis of said variable voltage in addition to the sensed d.c. voltage level.

14. A d.c. power supply comprising a main circuit and a control unit;

said main circuit including a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage; and

a switching element connected to said rectifier circuit and 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; and

said control unit including a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit comprising first means for sensing the level of said d.c. voltage, second means for generating a pulse signal having said second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, and means for applying said pulse signal to the control electrode of said switching element, wherein said first control circuit further comprises fifth means for generating a predetermined constant voltage and means for applying the constant voltage to said third means in place of the output of the first 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.

15. A d.c. power supply comprising a main circuit and a control unit;

said main circuit including a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage; and

a switching element connected to said rectifier circuit and 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; and

said control unit including a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit comprising first means for sensing the level of said d.c. voltage, second means for generating a pulse signal having said second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, and means for applying said pulse signal to the control electrode of said switching element, wherein the first control circuit further comprises means for detecting the current flow through the main circuit, means for producing a voltage corresponding to the detected current flow and means for applying the voltage corresponding to the detected current flow to said third means in place of the output of said first means when the voltage corresponding to the detected current flow becomes greater than the output of said first means, so that the duty ratio of the pulse signal may vary in accordance with the current flow of the main circuit.

16. A d.c. power supply comprising a main circuit and a control unit;

said main circuit including a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage; and

a switching element connected to said rectifier circuit and 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; and

said control unit including a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit comprising first means for sensing the level of said d.c. voltage, second means for generating a pulse signal having said second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, and means for applying said pulse signal to the control electrode of said switching element, wherein said control unit further comprises a second control circuit including means for producing a predetermined constant voltage, comparing means for comparing the sensed d.c. voltage obtained by said first means with said predetermined constant voltage to produce an output when the sensed d.c. voltage is greater than said predetermined constant voltage, and gate means connected to receive outputs of said comparing means and said first control circuit for inhibiting the application of the output of the first control circuit to the control electrode of said switching element in response to the output of said comparing means.

17. A d.c. power supply comprising a main circuit and a control unit;

said main circuit including a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage; and

a switching element connected to said rectifier circuit and 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; and

said control unit including a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit comprising first means for sensing the level of said d.c. voltage, second means for generating a pulse signal having said second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, and means for applying said pulse signal to the control electrode of said switching element, wherein said control unit further comprises a third control circuit including means for producing a predetermined constant current, detecting means for detecting the current flow passing through said main circuit, comparing means for comparing said detected current with said predetermined constant current to generate an output when the detected current becomes greater in level than the predetermined constant current, and gate means connected to receive the outputs of the comparing means and the first control circuit for inhibiting the application of the output of the first control circuit to the control electrode of said switching element in response to the output of the comparing means.

18. A d.c. power supply having a main circuit and a control unit;

said main circuit comprising

a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage;

a switching element connected to said rectifier circuit and 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 having a primary winding and a secondary winding, said primary winding being connected to said switching element such that a chopped current flows in one direction therethrough; and

smoothing means connected to the secondary winding of said transformer to smooth the voltage developed thereacross;

said control unit comprising a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit including first means for sensing the level of said d.c. voltage, second means for generating a pulse signal having said second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, and means for applying said pulse signal to the control electrode of said switching element, wherein the control unit further comprises a fourth control circuit including detecting means for detecting the voltage developed across the primary winding of said transformer and a voltage across said switching element, means for producing a predetermined voltage, comparing means for comparing at least one of the detected voltages with said predetermined voltage to produce an output when one becomes greater than the other, and gate means connected to receive outputs of said comparing means and said first control circuit for inhibiting the application of the output of said first control circuit to the control electrode of said switching element in response to the output of said comparing means.

19. A d.c. power supply comprising a main circuit and a control unit;

said main circuit including a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage; and

a switching element connected to said rectifier circuit and 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; and

said control unit including a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit comprising first means for sensing the level of said d.c. voltage, second means for generating a pulse signal having said second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means becomes lower, and means for applying said pulse signal to the control electrode of said switching element, wherein a condenser is connected across the rectifier circuit, said condenser being selected to have a value which exhibits a low impedance at said second frequency.

20. A d.c. power supply having a main circuit and a control unit;

said main circuit comprising

a voltage source providing an a.c. voltage having a predetermined first frequency;

a rectifier circuit connected to said voltage source for converting said a.c. voltage into a d.c. voltage;

a switching element connected to said rectifier circuit and 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 having a primary winding and a secondary winding, said primary winding being connected to said switching element such that a chopped current flows in one direction therethrough; and

smoothing means connected to the secondary winding of said transformer to smooth the voltage developed thereacross;

said control unit comprising a first control circuit for controlling the ON-OFF operation of the switching element of said main circuit, said first control circuit including first means for sensing the level of said d.c. voltage, second means for generating a pulse signal having said second frequency, third means for controlling a duty ratio of said pulse signal in response to the output of the first means in such a manner that the duty ratio becomes greater as the output of the first means become lower, and means for applying said pulse signal to the control electrode of said switching element, wherein said transformer comprises a magnetic core defining a magnetic path on which the primary and secondary windings are wound, said magnetic path including a permanent magnet to provide a predetermined magnetic bias with respect to magnetic flux due to a current flowing through the primary winding.