Inverter type switching power supply with transformer and short circuit arrangement therefor

• US 4,737,974 A
• Filed: 01/14/1985
• Issued: 04/12/1988
• Est. Priority Date: 01/17/1984
• Status: Expired due to Fees

• Current Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Inventors: Hino, Hirofumi, Kaneko, Kazuo, Ohtakeguchi, Masaji, Tokunaga, Norikazu
• Primary Examiner(s): Church, Craig E.
• Application Number:
  US06/691,126
• Time in Patent Office: 1,184 Days
• Field of Search: 378/101, 378/104, 378/105, 378/107, 363/17, 363/24, 363/41
• US Class Current: 378/105
• CPC Class Codes: H02M 3/22 with intermediate conversion into ac
• CPC Class Codes: H02M 3/33573 Full-bridge at primary side of an isolation transformer
• CPC Class Codes: H02M 3/337 in push-pull configuration H02M3/33576 takes precedence; with self-oscillating arrangements H02M3/3382, H02M3/3385
• CPC Class Codes: H02M 3/3372 of the parallel type

Abstract

An inverter-type switching power supply circuit which comprises an inverter for converting the DC output of a DC power source to an AC output, a transformer for receiving the AC output of the inverter, a rectifier for rectifying the output of the transformer, a smoothing capacitor for smoothing the output of the rectifier and supplying it to a load, and a transformer short-circuiting circuit for short-circuiting either the primary side or the secondary side of the transformer. The transformer is frequency controlled such that the product of the applied voltage and time of the transformer becomes constant. Thus, the transformer can be designed to have a small size and a light weight.

Claims

1. A method of controlling a full-bridge type inverter used in an inverter type switching power supply circuit including:

a transformer having at least a primary winding and a secondary winding;

a full-bridge type inverter for converting a DC power source to an AC voltage to be supplied to said primary winding, said inverter including a series circuit of a first switching element connected to a first polarity terminal of said DC power source and a second switching element connected to a second polarity terminal of said DC power source, first and second diodes connected in anti-parallel with said first and second switching elements of said series circuit, respectively, another series circuit of a third switching element connected to said first polarity terminal of said DC power source and a fourth switching element connected to said second polarity terminal of said DC power source, and third and fourth diodes connected in anti-parallel with said third and fourth switching elements of said another series circuit, respectively, and wherein one end of said primary winding is connected to the connecting point of said first and second switching elements and another end of said primary winding is connected to the connecting point of said third and fourth switching elements;

rectrifier means connected to said secondary winding for rectifying the output of said transformer; and

smoothing capacitor means for smoothing the output of said rectifier means and supplying the smoothed output to a load;

the method comprising;

a first step of turning on said first switching element and simultaneously turning off said second switching element, while said fourth switching element is maintained on and said third switching element is maintained off to provide an on-period;

a second step of, upon elapse of the on-period after initiation of said first step, turning off said first switching element and simultaneously turning on said second switching element, while maintaining said third and fourth switching elements in the off and on states, respectively, to provide an off-period;

a third step of, upon elapse of the off-period since initiation of said second step, turing off said fourth switching element and simultaneously turning on said third switching element, while maintaining said first and second switching element in the off and on states, respectively, to provide another on-period;

a fourth step of, upon elapse of the another on-period since initiation of said third step, turning on said fourth switching element and simultaneously turning off said third switching element, while maintaining said first and second elements in off and on states, respectively, to provide another off-period; and

a fifth step of returning to said first step upon elapse of the another off-period since initiation of said fourth step and wherein the step of short-circuiting said transformer during the off-periods includes establishing two paths forming a bidirectional low-impedance path, one of said two paths being constituted by said primary winding, said second switching element and said fourth diode and the other of said two paths being constituted by said primary winding, said fourth switching element and said second diode, and maintaining on said second and fourth switching elements during the off-periods

2. A method according to claim 1, wherein the step of short-circuiting said transformer during the off-periods enables a damped oscillation of an electric charge stored in a stray capacitance of said transformer so as to discharge the electric charge stored in the stray capacitance of said transformer during the off periods.

3. A method according to claim 1, wherein the on-periods have a time length equal to a fixed predetermined value and the time lengths of said off-periods are variable.

4. A method according to claim 1, wherein the load includes an X-ray tube.

5. A switching power supply circuit using a full-bridge type inverter comprising:

a transformer having at least a primary winding and a secondary winding;

a full-bridge type inverter for converting a DC power source to an AC voltage to be supplied to said primary winding, said inverter including a series circuit of a first switching element connected to a first polarity terminal of said DC power source and a second switching element connected to a second polarity terminal of said DC power source, first and second diodes connected in anti-parallel with said first and second switching elements of said series circuit, respectively, another series circuit of a third switching element connected to said first polarity terminal of said DC power source and a fourth switching element connected to said second polarity terminal of said DC power source, and third and fourth diodes connected in anti-parallel with said third and fourth switching elements of said another series circuit, respectively, and wherein one end of said primary winding is connected to the connecting point of siad first and second switching elements and another end of said primary winding is connected to the connecting point of said third and fourth switching elements;

rectifier means connected to said secondary winding for rectifying the output of said transformer;

smoothing capacitor means for smoothing the output of said rectifier means and supplying the smoothed output to a load;

control means for controlling said inverter such that simultaneous turn-on of said first and fourth switching elements for an on-period and simultaneous turn-off of said third and second switching elements for said on-period are alternately repeated with an off-period inserted between the on-period and the next on-period; and

short-circuit means for short-circuiting a stray capacitance of said transformer during said off-period so as to discharge an electric charge stored in said stray capacitance, said short-circuit means including a bidirectional low-impedance path means including two paths each of said two paths containing said primary winding, one of said first to fourth switching elements and one of said first to fourth diodes, said control means maintaining on said one of said first to fourth switching elements of each of said two paths during said off-period.

6. A switching power supply circuit according to claim 22, wherein one of said two paths is constituted of said primary winding, said second switching element and said fourth diode, and the other of said two paths is constituted of said primary winding, said fourth switching element and said second diode, said control means maintaining on said second and fourth switching elements during said off-period.

7. A switching power supply circuit according to claim 22, wherein said short-circuit means enables a damped oscillation of the electric change stored in said stray capacitance during said off-period so as to discharge the electric charge stored in said stray capacitance.

8. A power supply circuit according to claim 22, wherein said on-period has a predetermined fixed time length and a time length of said off-period is variable.

9. A power supply circuit according to claim 22, wherein said load is an X-ray tube.