DC power-supply unit

• US 5,479,336 A
• Filed: 08/04/1993
• Issued: 12/26/1995
• Est. Priority Date: 08/06/1992
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Suzuki, Itsuo, Kato, Yoshiro, Suga, Ikura, Motoki, Takahiro, Iio, Koji, Ohnishi, Yoshitaka
• Primary Examiner(s): Sterrett, Jeffrey L.
• Application Number:
  US08/102,103
• Time in Patent Office: 874 Days
• Field of Search: 323/210, 323/222, 323/282, 323/285, 323/299, 323/351, 363/44, 363/89, 363/126
• US Class Current: 363/89
• CPC Class Codes: H02M 1/0085 Partially controlled bridges
• CPC Class Codes: H02M 1/4208 Arrangements for improving power factor of AC input
• CPC Class Codes: H02M 1/4225 using a non-isolated boost converter
• 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
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Abstract

A DC power-supply unit convening AC into DC power is provided to, when AC voltage and/or AC current of an AC power supply passes through a zero point, close a switch after a preset first delay time from a passing through time, and open the switch after a preset second delay time from a passing through time. The unit includes a rectifier switch for convening AC power output from the AC power supply into DC power, an inductive element connected to the rectifying element, a switching element connected to the inductive element, and the rectifying element, a smoothing unit connected in parallel with the switching element, and a switch control unit for controlling the switch according to the predetermined delay times.

Claims

1. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

switch controlling means in which first and second delay times are preset so as to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said preset first delay time from a passing through time, and open said switching means after said second delay time form said passing through time.

13. A dc power-supply unit according to any one of claims 1 to 12, further comprising correcting means for detecting a power factor of ac power output from said ac power supply, and comparing said power factor with a predetermined value so as to correct said first delay time which is set in said switch controlling means to close said switching means depending upon results of a comparison.

14. A dc power-supply unit according to claim 1, further comprising correcting means for detecting a power factor of ac power output from said ac power supply, and comparing said power factor with a predetermined value so as to correct said second delay time which is set in said switch controlling means to open said switching means depending upon results of a comparison.

15. A dc power-supply unit according to any one of claims 1 to 12, further comprising correcting means for detecting a relative harmonic content in ac power output from said ac power supply, and comparing said relative harmonic content with a predetermined value so as to correct said first delay time which is set in said switch controlling means to close said switching means depending upon results of a comparison.

16. A dc power-supply unit according to claim 1, further comprising correcting means for detecting a relative harmonic content in ac power output from said ac power supply, and comparing said relative harmonic content with a predetermined value so as to correct said second delay time which is set in said switch controlling means to open said switching means depending upon results of a comparison.

17. A dc power-supply unit according to any one of claims 1 to 12, further comprising correcting means for detecting distortion in a waveform of said ac power supply, and comparing said distortion in said waveform with a predetermined value so as to correct said first delay time which is set in said switch controlling means to close said switching means depending upon results of a comparison.

18. A dc power-supply unit according to claim 1, further comprising correcting means for detecting distortion in a waveform of said ac power supply, and comparing said distortion in said waveform with a predetermined value so as to correct said second delay time which is set in said switch controlling means to open said switching means depending upon results of a comparison.

19. A dc power-supply unit according to claim 1, further comprising correcting means for detecting a power factor and a relative harmonic content of ac power output from said ac power supply, and comparing said power factor with a predetermined value so as to correct a first delay time which is set in said switch controlling means to close said switching means depending upon results of a comparison, and comparing said relative harmonic content with a predetermined value so as to correct said second delay time which is set in said switch controlling means to open said switching means depending upon results of a comparison.

20. A dc power-supply unit according to claim 1, further comprising correcting means for detecting a power factor and a relative harmonic content of ac power output from said ac power supply, and comparing said relative harmonic content with a predetermined value so as to correct said first delay time which is set in said switch controlling means to close said switching means depending upon results of a comparison, and comparing said power factor with a predetermined value so as to correct a second delay time which is set in said switch controlling means to open said switching means depending upon results of a comparison.

21. A dc power-supply unit according to any one of claims 1 to 12, wherein said side to which said inductive element is connected between one terminal of said rectifying means and said ac power supply is the ac side.

22. A dc power-supply unit according to any one of claims 1 to 12, wherein said switch controlling means repeatedly opens and closes said switching means at predetermined intervals until said switching means is opened after said switching means is closed.

23. A dc power-supply unit according to any one of claims 1 to 12, wherein said side to which said inductive element is connected between one terminal of said rectifying means and said ac power supply is the dc side.

2. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

switch controlling means in which a first delay time is preset so as to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said first delay time from a passing through time, and open said switching means after a predetermined time period from a closing time.

3. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

short-circuit current detecting means for detecting short-circuit current flowing in said inductive element; and

switch controlling means in which a first delay time is preset so as to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said delay time from a passing through time, and open said switching means when a value of said short-circuit current becomes a predetermined value after a closing operation.

4. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load is preset to be shorter than a second delay time under a heavy load, and a third delay time is preset to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon the results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and so as to open said switching means after said third delay time from said passing through time.

5. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on the side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay under a light load is preset, and a second delay time under a heavy load is preset to be shorter than said first delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and so as to open said switching means after a predetermined time period from a closing time.

6. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on the side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

short-circuit current detecting means for detecting short-circuit current flowing in said inductive element;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load is preset, and a second delay time under a heavy load is preset to be shorter than said first delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and so as to open said switching means when a value of said short-circuit current becomes a predetermined value after a closing operation.

7. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time and a second delay time under a light load are preset, and a third delay time under a heavy load is preset to be longer than said second delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said first delay time from a passing through time, and select said second delay time or said third delay time depending upon the results of the detection of said load condition detecting means so as to open said switching means after a selected delay time from said passing through time.

8. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time and a second delay time under a light load are preset, and a third delay time under a heavy load is preset to be longer than said second delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said first delay time from a passing through time, and select said second delay time or said third delay time depending upon results of detection of said load condition detecting means so as to open said switching means after a selected delay time from a closing operation.

9. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

short-circuit current detecting means for detecting short-circuit current flowing in said inductive element;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time is preset to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said delay time from a passing through time, and detect depending upon said load condition detecting means whether or not a value of said short-circuit current becomes a value preset according to said magnitude of said load after a closing operation so as to open said switch means when a decision is made that said short-circuit current becomes said predetermined value.

10. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element, and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load and a second delay time under a heavy load are preset such that said second delay time under said heavy load is shorter than said first delay time under said light load, and a third delay time under a light load and a fourth delay time under a heavy load are preset such that said fourth delay time under said heavy load is longer than said third delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and to select said third delay time or said fourth delay time depending upon results of said detection of said load condition detecting means so as to open said switching means after a selected delay time from said passing through time.

11. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load and a second delay time under a heavy load are preset such that said second delay time under said heavy load is shorter than said first delay time under said light load, and a third delay time under a light load and a fourth delay time under a heavy load are preset such that said fourth delay time under said heavy load is longer than said third delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and to select said third delay time or said fourth delay time depending upon results of said detection of said load condition detecting means so as to open said switching means after a selected delay time from a closing time.

12. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

short-circuit current detecting means for detecting short-circuit current flowing in said inductive element;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load and a second delay time under a heavy load are preset such that said second delay time under said heavy load is shorter than said first delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and to detect depending upon said load condition detecting means whether or not a value of said short-circuit current becomes a predetermined value preset according to said magnitude of said load after a closing operation so as to open said switching means when a decision is made that said short-circuit current becomes said predetermined value.

24. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load and a second delay time under a heavy load are preset such that said second delay time under said heavy load is shorter than said first delay time under said light load, and a third delay time under a light load and a fourth delay time under a heavy load are preset such that said fourth delay time under said heavy load is longer than said third delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and to select said third delay time or said fourth delay time depending upon results of said detection of said load condition detecting means so as to open said switching means after a selected delay time from a closing time.

25. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

short-circuit current detecting means for detecting short-circuit current flowing in said inductive element;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load and a second delay time under a heavy load are preset such that said second delay time under said heavy load is shorter than said first delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon the results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and to detect depending upon said load condition detecting means whether or not a value of said short-circuit current becomes a predetermined value preset according to said magnitude of said load after a closing operation so as to open said switching means when a decision is made that said short-circuit current becomes said predetermined value.

26. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

overvoltage detecting means for detecting overvoltage across said smoothing means; and

switch controlling means in which a delay time is preset so as to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said delay time from a passing through time, and open said switching means when said overvoltage is detected by said overvoltage detecting means.

27. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

overvoltage detecting means for detecting overvoltage across said smoothing means;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load is preset, and a second delay time under a heavy load is preset to be shorter than said first delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and so as to open said switching means when said overvoltage is detected by said overvoltage detecting means.

28. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means to perform a switching operation; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

overvoltage detecting means for detecting overvoltage across said smoothing means;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a delay time is preset to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said delay time from a passing through time, and detect depending upon said load condition detecting means whether or not a value of said short-circuit current becomes a value preset according to said magnitude of said load after a closing operation so as to open said switch means when said overvoltage is detected by said overvoltage detecting means.

29. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means;

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

switch controlling means in which first and second delay times are preset so as to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said preset first delay time from a passing through time, and open said switching means after said second delay time from said passing through time.

30. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means;

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

switch controlling means in which a delay time is preset so as to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said delay time from a passing through time, and open said switching means after a predetermined time period from a closing time.

31. A dc power-supply unit comprising:

rectifying means for convening ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means;

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

short-circuit current detecting means for detecting short-circuit current flowing in said inductive element; and

switch controlling means in which a delay time is preset so as to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said delay time from a passing through time, and open said switching means when a value of said short-circuit current becomes a predetermined value after a closing operation.

32. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load is preset to be shorter than a second delay time under a heavy load, and a third delay time is preset to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and so as to open said switching means after said third delay time from said passing through time.

33. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay under a light load is preset, and a second delay time under a heavy load is preset to be shorter than said first delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and so as to open said switching means after a predetermined time period from a closing time.

34. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

short-circuit current detecting means for detecting short-circuit current flowing in said inductive element;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load is preset, and a second delay time under a heavy load is preset to be shorter than said first delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and so as to open said switching means when a value of said short-circuit current becomes a predetermined value after a closing operation.

35. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time and a second delay time under a light load are preset, and a third delay time under a heavy load is preset to be longer than said second delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said first delay time from a passing through time, and select said second delay time or said third delay time depending upon results of detection of said load condition detecting means so as to open said switching means after a selected delay time from said passing through time.

36. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time and a second delay time under a light load are preset, and a third delay time under a heavy load is preset to be longer than said second delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said first delay time from a passing through time, and select said second delay time or said third delay time depending upon results of detection of said load condition detecting means so as to open said switching means after a selected delay time from a closing operation.

37. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

short-circuit current detecting means for detecting short-circuit current flowing in said inductive element;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a delay time is preset to, when ac voltage and/or ac current of said ac power supply passes through a zero point, close said switching means after said delay time from a passing through time, and detect depending upon said load condition detecting means whether or not a value of said short-circuit current becomes a value preset according to said magnitude of said load after a closing operation so as to open said switch means when a decision is made that said short-circuit current becomes said predetermined value.

38. A dc power-supply unit comprising:

rectifying means for converting ac power output from an ac power supply into dc power so as to feed to a load;

an inductive element whose one end is connected to one terminal on a side of said rectifying means;

switching means connected between the other end of said inductive element, and the other terminal on said side of said rectifying means for short-circuiting at least one of a plurality of rectifying devices forming said rectifying means; and

smoothing means connected in parallel with said switching means, and said dc power-supply unit further comprising;

load condition detecting means for detecting magnitude of said load; and

switch controlling means in which a first delay time under a light load and a second delay time under a heavy load are preset such that said second delay time under said heavy load is shorter than said first delay time under said light load, and a third delay time under a light load and a fourth delay time under a heavy load are preset such that said fourth delay time under said heavy load is longer than said third delay time under said light load to, when ac voltage and/or ac current of said ac power supply passes through a zero point, select said first delay time or said second delay time depending upon results of detection of said load condition detecting means so as to close said switching means after a selected delay time from a passing through time, and to select said third delay time or said fourth delay time depending upon results of said detection of said load condition detecting means so as to open said switching means after a selected delay time from said passing through time.