Step-down converter having a resonant inductor, a resonant capacitor and a hybrid transformer

• US 7,915,874 B1
• Filed: 10/04/2010
• Issued: 03/29/2011
• Est. Priority Date: 10/04/2010
• Status: Expired due to Fees

• Current Assignee: CUKS LLC
• Original Assignee: CUKS LLC
• Inventors: Cuk, Slobodan
• Primary Examiner(s): Riley; Shawn
• Application Number:
  US12/924,743
• Time in Patent Office: 176 Days
• Field of Search: 323/224, 323/233, 323/288, 323/290, 323/293, 323/259
• US Class Current: 323/224
• CPC Class Codes: H02M 3/005 using Cuk converters
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• 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

Unlike buck converter and tapped-inductor buck converters, which use only inductive energy transfer, the present invention employs the capacitive energy transfer in addition to inductive energy transfer. The hybrid transformer performs the double duty simultaneously: transfers the input inductive energy storage to the load through a taped-inductor turns ratio n but also transfers the resonant capacitor discharge current to the load during OFF-time interval amplified by turns ratio m of the hybrid transformer.

Despite the presence of the resonant inductor current during the OFF-time interval, the output voltage is neither dependent on resonant component values nor on the load current as in conventional resonant converters but depends on duty ratio D and turns ratio n of the hybrid transformer. Hence a simple regulation of output voltage is achieved using duty ratio control.

Claims

1. A switching DC-to-DC converter for providing power from a DC voltage source connected between an input terminal and a common terminal to a DC load connected between an output terminal and said common terminal, said converter comprising:

a first switch with one end connected to said input terminal;

a second switch with one end connected to another end of said first switch;

a current rectifier switch with anode end connected to said common terminal;

a resonant inductor with one end connected to another end of said second switch and another end of said resonant inductor connected to said output terminal;

a resonant capacitor with one end connected to said another end of said first switch;

a first winding of a hybrid transformer with an unmarked end connected to another end of said resonant capacitor and a dot-marked end connected to cathode end of said current rectifier switch;

a second winding of said hybrid transformer with an unmarked end connected to said dot-marked end of said first winding, and a dot-marked end of said second winding connected to said output terminal;

switching means for keeping said first switch ON and said second switch and said current rectifier switch OFF during T_ON time interval, and keeping said first switch OFF and said second switch and said current rectifier switch ON during T_OFF time interval, where said T_ON time interval and said T_OFF time interval are complementary time intervals within one switch operating cycle T_S;

wherein said resonant inductor and said resonant capacitor form a resonant circuit during said T_OFF time interval with a resonant current flowing through said first winding into said DC load;

wherein a first turns ratio n of said hybrid transformer is a total number of turns of both said first winding and said second winding divided by a number of turns of said second winding of said transformer,

wherein an input current during said T_ON time interval stores an inductive energy in said first and said second winding and during said T_OFF time interval said stored inductive energy is transferred to said DC load through said second winding by n times higher current than said input current,

wherein a second turns ratio m of said hybrid transformer is the ratio between number of turns of said first winding and said second winding,

wherein said resonant current in said first winding is amplified by said second turns ratio m of said hybrid transformer and sent to said DC load through said second winding of said transformer,

wherein a duty ratio D is ratio between said T_ON time interval and said switching operating cycle T_S, and

wherein a DC-to-DC voltage step-down conversion ratio of said converter depends on said duty ratio D and said first turns ratio n of said hybrid transformer.

2. A converter as defined in claim 1,

wherein said first switch and said second switch are semiconductor bipolar transistors;

wherein said switching means include precise electronically controlling operation of said first switch relative to said second switch, whereby two transition intervals, a first transition interval and a second transition interval are created during which said first switch and said second switch are turned OFF, and

whereby said first and said second transition intervals are adjusted to minimize switching losses of said first switch and said second switch.

3. A converter as defined in claim 2,

wherein said first switch and said second switch are semiconductor MOSFET transistors, and

whereby said first switch and said second switch have substantially reduced conduction losses.

4. A converter as defined in claim 3,

wherein said current rectifier switch is a semiconductor MOSFET transistor,

wherein said switching means keep said semiconductor MOSFET transistor ON during said T_OFF time interval and OFF during said T_ON time interval, and

whereby said semiconductor MOSFET transistor has substantially reduced conduction losses.

5. A converter as defined in claim 1,

wherein an additional converter, same as said converter in claim 1, is connected in parallel to said converter in claim 1;

wherein both said converters operate at equal duty ratios of D=0.5;

wherein said additional converter operates out of phase with said converter of claim 1 so that when said first switch is turned ON, a first switch of said additional converter is turned OFF, and

whereby voltage at said DC load has substantially reduced ripple voltage.

6. A converter as defined in claim 1,

wherein said unmarked end of said second winding is connected to said unmarked end of said first winding of said transformer, and said dot-marked end of said second winding is connected to said cathode end of said current rectifier switch;

wherein said dot-marked end of said first winding of said hybrid transformer is connected to said output terminal,

wherein a DC-to-DC voltage step-down conversion ratio of said converter depends on said duty ratio D and said second turns ratio m between said first winding and said second winding of said hybrid transformer.

7. A converter as defined in claim 6,

wherein said unmarked end of said second winding of said hybrid transformer is connected to said cathode end of said current rectifier switch and said dot-marked end of said second winding of said hybrid transformer is connected to said output terminal;

wherein a DC-to-DC voltage step-down conversion ratio of said converter depends on said duty ratio D and said second turns ratio m between said first winding and said second winding of said hybrid transformer.

8. A switching DC-to-DC converter for providing power from a DC voltage source connected between an input terminal and a common terminal to a DC load connected between an output terminal and said common terminal, said converter comprising:

a first switch with one end connected to said input terminal;

a second switch with one end connected to another end of said first switch;

a current rectifier switch with anode end connected to said common terminal;

a resonant inductor with one end connected to another end of said second switch and another end of said resonant inductor connected to cathode end of the said rectifier switch;

a resonant capacitor with one end connected to said another end of said first switch;

a first winding of a hybrid transformer with an unmarked end connected to another end of said resonant capacitor and a dot-marked end connected to said cathode end of said current rectifier switch;

a second winding of said hybrid transformer with an unmarked end connected to said dot-marked end of said first winding, and a dot-marked end of said second winding connected to said output terminal;

switching means for keeping said first switch ON and said second switch and said current rectifier switch OFF during T_ON time interval, and keeping said first switch OFF and said second switch and said current rectifier switch ON during T_OFF time interval, where said T_ON time interval and said T_OFF time interval are complementary time intervals within one switch operating cycle T_S;

wherein said resonant inductor and said resonant capacitor form a resonant circuit during said T_OFF time interval with a resonant current flowing through said first winding of said hybrid transformer;

wherein a first turns ratio n of said hybrid transformer is a total number of turns of both said first winding and said second winding divided by a number of turns of said second winding of said hybrid transformer,

wherein an input current during said T_ON time interval stores an inductive energy in said first and said second winding and during said T_OFF time interval said stored inductive energy is transferred to said DC load through said second winding by n times higher current than said input current,

wherein a second turns ratio m of said hybrid transformer is the ratio between number of turns of said first winding and said second winding,

wherein said resonant current in the said first winding is amplified by the said second turns ratio m of said hybrid transformer and sent to said DC load through said second winding of said transformer,

wherein a duty ratio D is ratio between said T_ON time interval and said switching operating cycle T_S, and

wherein a DC-to-DC voltage step-down conversion ratio of said converter depends on said duty ratio D and said first turns ratio n of said hybrid transformer.

9. A converter as defined in claim 8,

wherein said first switch and said second switch are semiconductor bipolar transistors;

wherein said switching means include precise electronically controlling operation of said first switch relative to said second switch, whereby two transition intervals, a first transition interval and a second transition interval are created during which said first switch and said second switch are turned OFF, and

whereby said first and said second transition intervals are adjusted to minimize switching losses of said first switch and said second switch.

10. A converter as defined in claim 9,

wherein said first switch and said second switch are semiconductor MOSFET transistors, and

whereby said first switch and said second switch have substantially reduced conduction losses.

11. A converter as defined in claim 10,

wherein said current rectifier switch is a semiconductor MOSFET transistor,

wherein said switching means keep said semiconductor MOSFET transistor ON during said T_OFF time interval and OFF during said T_ON time interval, and

whereby said semiconductor MOSFET transistor has substantially reduced conduction losses.

12. A converter as defined in claim 8,

wherein an additional converter, same as said converter in claim 8, is connected in parallel to said converter in claim 8;

wherein both said converters operate at equal duty ratios of D=0.5;

wherein said additional converter operates out of phase with said converter of claim 8 so that when said first switch is turned ON, a first switch of said additional converter is turned OFF, and

whereby voltage at said DC load has substantially reduced ripple voltage.

13. A converter as defined in claim 8,

wherein said unmarked end of said second winding is connected to said unmarked end of said first winding of said transformer, and said dot-marked end of said second winding is connected to said cathode end of said current rectifier switch;

wherein said dot-marked end of said first winding of said hybrid transformer is connected to said output terminal,

wherein a DC-to-DC voltage step-down conversion ratio of said converter depends on said duty ratio D and said second turns ratio m between said first winding and said second winding of said hybrid transformer.

14. A converter as defined in claim 13,

wherein said unmarked end of said second winding of said hybrid transformer is connected to said cathode end of said current rectifier switch and said dot-marked end of said second winding of said hybrid transformer is connected to said output terminal;

wherein a DC-to-DC voltage step-down conversion ratio of said converter depends on said duty ratio D and said second turns ratio m between said first winding and said second winding of said hybrid transformer.

15. A converter as defined in claim 8,

wherein said another end of said resonant inductor is connected to said common terminal.

16. A hybrid switching method for non-isolated large step-down DC-to-DC power conversion comprising:

providing a main controllable three-terminal switch conducting and supplying current to a DC load during an ON-time interval T_ON and non-conducting during an OFF-time interval T_OFF within a switching time period T_S where D is a controllable duty ratio;

providing a complementary controllable three-terminal switch and a two-terminal current rectifier switch conducting and supplying current to said DC load during said OFF-time interval T_OFF and non-conducting during said ON-time interval T_ON;

providing first and second winding of a hybrid transformer operating and being flux-balanced during the entire said switching time period T_S;

providing said hybrid transformer with a first turns ratio n being a ratio of the sum of said first and second winding turns divided by said second winding turns,

providing said hybrid transformer with a second turns ratio m being a ratio between said first winding turns and said second winding turns,

providing a resonant inductor operating and being flux-balanced during said OFF-time interval T_OFF;

providing said first and said second winding of said hybrid transformer store an inductive energy during said ON-time interval T_ON and release said inductive energy through said second winding and said two-terminal current rectifier switch to said DC load during said OFF-time interval T_OFF;

providing a resonant capacitor which stores a capacitive energy during said ON-time interval T_ON and releases said capacitive energy during said OFF-time interval T_OFF by both a resonant current directly to said DC load through said first winding and by an amplified resonant current in said second winding by said turns ratio m of said hybrid transformer to said DC load;

providing said resonant inductor and said resonant capacitor form a resonant circuit during said OFF-time interval T_OFF having a constant resonant period two times longer than said OFF-time interval T_OFF;

wherein a duty ratio D is ratio between said T_ON time interval and said switching operating cycle T_S, and

wherein a DC-to-DC voltage step-down conversion ratio of said converter depends on said duty ratio D and said first turns ratio n of said hybrid transformer,

controlling said duty ratio D at constant switching frequency to regulate output DC voltage against input voltage and/or load current changes.

17. A hybrid switching method for non-isolated large step-down DC-to-DC power conversion as in claim 16 wherein a switching frequency is controlled to keep said OFF-time period constant and thereby improve efficiency.

18. A hybrid switching method for non-isolated large step-down DC-to-DC power conversion as defined in claim 16 wherein said main and said complementary controllable three-terminal switches are MOSFET transistors.

19. A hybrid switching method for non-isolated large step-down DC-to-DC power conversion as defined in claim 18 wherein said two-terminal current rectifier switch is replaced with a MOSFET transistor being turned ON and OFF as a synchronous rectifier to reduce conduction losses.

20. A hybrid switching method for non-isolated large step-down DC-to-DC power conversion as defined in claim 16 wherein two equal converters operate in parallel and out-of-phase at the same duty ratio D=0.5 providing substantially reduced voltage ripple at said output DC load.