DC-to-DC switching converter with zero input and output current ripple and integrated magnetics circuits

• US 4,257,087 A
• Filed: 04/02/1979
• Issued: 03/17/1981
• Est. Priority Date: 04/02/1979
• Status: Expired due to Term

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Cuk, Slobodan M.
• Primary Examiner(s): Shoop, William M.
• Application Number:
  US06/026,541
• Time in Patent Office: 715 Days
• Field of Search: 363/16, 363/20, 363/39, 363/40, 363/45, 363/124, 363/131
• US Class Current: 363/16
• CPC Class Codes: H02M 3/005 using Cuk converters
• CPC Class Codes: H02M 3/33538 of the forward type H02M3/3353, H02M3/33569 take precedence

Abstract

An improved dc-to-dc converter is provided comprised of two inductances, an input inductance in series with the input source and an output inductance in series with the load, and between the two inductances, two storage capacitances in series with the two inductances. Switching means alternately connect the junction between the input inductance and the first series capacitance, and the junction between the second capacitance and output inductance, to a junction common to the source and load. A third inductance is connected between the junction of the two capacitances and the return current paths for the source and load.

In one of the embodiments of the invention, all three inductances are combined on the same core thus comprising a single magnetic circuit with three windings. In another embodiment of the invention an isolation transformer is first used to replace the third inductance. Again, both input and output inductor and isolation transformer are merged into a single magnetic circuit with four windings. In any of the embodiments of the invention, a zero current ripple can be obtained at both the input and the output simultaneously by a proper design of the magnetic circuit. A new method of integrated magnetics design is then disclosed to improve performance of other converter structures by properly merging their magnetics components.

Claims

1. In a dc-to-dc switching converter comprised of an input inductance connected in series with a source, an output inductance connected in series with a load, storage capacitance connected in series between said input inductance and output inductance, and switching means for alternatively connecting a junction between said input inductance and said storage capacitance, and a junction between said storage capacitance and said output inductance, to respective return current paths for said source and load, said storage capacitance being divided into a first capacitor in series with said input inductance and a second capacitor in series with said output inductance, an improvement comprising electromagnetic induction means for connecting said first capacitor to the return current path for said source and connecting said second capacitor to the return current path for said load, and said electromagnetic induction means having at least one winding and a magnetic circuit with at least two flux paths, one flux path for coupling said input inductance and a winding of said induction means, and another flux path for coupling said output inductance and a winding of said induction means.

2. An improvement as defined in claim 1 wherein said magnetic induction means are comprised of two windings electrically connected in parallel and magnetically isolated, by being on two separate cores with one winding being on one core with said input inductor and the other winding being on the other core with said output inductor.

3. An improvement as defined in claim 1 wherein said magnetic circuit is comprised of a single core having two flux paths with a common branch and only one winding on said common branch with said input inductance on one separate branch of one flux path, and said output inductance on another separate branch of the other flux path.

4. An improvement as defined in claim 1 wherein said magnetic circuit is comprised of an isolation transformer having a primary winding connected in series between said first capacitor and the return current path of said source, said primary winding being inductively coupled to said input inductance, and a secondary winding connected in series between said second capacitor and return current path of said load, said secondary winding being inductively coupled to said output inductance.

5. An improvement as defined in claim 4 wherein said dc-to-dc converter has an additional output inductance for supplying current to an additional load and an additional storage capacitor in series with said additional output inductance, and said switching means alternately connects a junction between said additional storage capacitor and additional output inductance to a return current path of said additional load, and said isolation transformer has an additional secondary winding connected in series between said additional capacitor and the return current path of said additional load, thereby to provide a separate output current to said additional load from said source, said additional output inductance being inductively coupled to said additional secondary winding and magnetically isolated from said input inductance and the other input inductance.

6. An improvement as defined in claim 1 wherein said magnetic circuit is comprised of an isolation transformer having a primary winding connected in series between said first capacitor and the return current path of said source and a secondary winding connected in series between said second capacitor and the return current path of said load, and a first inductance connected in parallel with said primary winding, said first inductance being inductively coupled to said input inductance and magnetically isolated from said output inductance, and a second inductance connected in parallel with said secondary winding, said second inductance being inductively coupled to said output inductance and magnetically isolated from said input inductance.

7. An improvement as defined in claim 1, 2, 3, 4, 5, or 6 wherein the coupling coefficients and turns ratios of said input inductance and a winding and of said output inductance and a winding are selected for a matching condition n_i =k_i, and n_i is equal to the square root of the ratio of self inductances of said winding L to the inductance L_i, where i is 1 to indicate input inductance L₁ for the matching condition of zero ripple in the input current from said source, and i is 2 to indicate output inductance L₂ for the matching condition of zero ripple in the output current to said load, and in claim 5, i is 3 to indicate output inductance L₃ for the matching condition of zero ripple in the output current to said additional load.

8. A dc-to-dc switching converter comprised of an input inductance connected in series to a source, an output inductance connected in series with a load, a first storage capacitance connected in series with said input inductance and said source, a second storage capacitance connected in series with said output inductance and said load, an isolation transformer between said first and second storage capacitances having its primary winding connected in series between said first storage capacitance and the return current path for said source and its secondary winding connected in series between said second storage capacitance and the return current path for said load, switching means for alternately connecting a junction between said input inductance and said first storage capacitance and a junction between said second storage capacitance and said output inductance, to respective return current paths for said source and load, means for inductively coupling said primary winding to said input inductance while maintaining said primary winding magnetically isolated from said output inductance, and means for inductively coupling said secondary winding to said output inductance while maintaining said secondary winding magnetically isolated from said input inductance.

9. A dc-to-dc switching converter as defined in claim 8 wherein said isolation transformer has an additional secondary winding connected in series sequence with an additional storage capacitance and output inductance to and additional load, and said switching means alternately connects a junction between said additional storage capacitance and additional output inductance to a return current path of said additional load, thereby to provide a separate output current to said additional load from said source, said additional output inductance being inductively coupled to said additional secondary winding and magnetically isolated from said input inductance and the other output inductance.

10. A dc-to-dc switching converter as defined in claim 8 wherein said primary and secondary windings are not respectively coupled to said input and output inductances, and instead a first additional winding connected in parallel with said primary winding is so coupled with said input inductance and a second additional winding connected in parallel with said secondary winding is so coupled with said output inductance.

11. A dc-to-dc switching converter as defined in claim 10 wherein said isolation transformer is omitted and said first and second additional windings are instead connected together in parallel.

12. A dc-to-dc switching converter as defined in claim 11 wherein said first and second additional windings are replaced by a single winding magnetically coupled to the input inductance and to the output inductance by said inductive coupling means while maintaining said input inductance magnetically isolated from said output inductance.

13. An improvement as defined in claim 8, 9, 10, 11 or 12 wherein the coupling coefficients and turns ratios between said input inductance and a winding and between said output inductance and a winding are selected for a matching condition n_i =k_i, and n_i is equal to the square root of the ratio of self inductance of said winding L to the inductance L_i, where i is 1 to indicate input inductance L₁ for the matching condition of zero ripple in the input current from said source, and i is 2 to indicate output inductance L₂ for the matching condition of zero ripple in the output current to said load, and in claim 9, i is 3 to indicate output inductance L₃ for the matching condition of zero ripple in the output current to said additional load.

14. A complex switching circuit in which a number of storage elements comprised of inductors, or inductors and transformers, and capacitors are interconnected with switches to perform a useful function, and in which windings of the separate inductors, or inductors and capacitors, are merged into an integral magnetic circuit with multiple flux paths sharing one common branch, and said windings are on separate branches of selected flux paths with one or more windings on said common branch, and in which windings have synchronized and proportional voltage waveforms, thereby to provide improved performance.

15. A complex switching circuit as defined in claim 14 wherein said storage elements are interconnected to perform as a converter, inverter or power amplifier, and the improved performance is reduced switching ripple at the input or output, or both the input or output of said circuit.

16. A complex switching circuit as defined in claim 15 wherein windings coupled are designed for a matching condition n_i =k_i, and n_i is equal to the square root of the ratio of self inductances L of said winding on said common path to the inductance L_i of the winding coupled to the winding on said common path, where i is set equal to an integer to indicate a particular one of said inductors for a reduction of ripple to a port of said circuit associated with the ith inductor.

17. A dc-to-dc switching converter having a source in series with an input inductance, an input energy storage capacitance, a primary winding of an isolation transformer, a return current path for said source, input switching means for periodically connecting a junction between said input inductance and said input energy storage capacitance to said return current path of said source, and means for inductively coupling said input inductance to said primary winding of said isolation transformer, and having an output energy storage capacitance connected in a current loop comprising a secondary of said isolation transformer and an output switching means, and a load connected in parallel with said output energy storage capacitance, said output switching means functioning to close the loop of said output energy storage capacitance and said secondary winding while said input switching means is not connecting the junction between said input inductance and said input energy storage capacitance to said return current path of said source.

18. A dc-to-dc switching converter having a load in series with an output inductance, an output energy storage capacitance, a secondary winding of an isolation transformer, a return current path for said load, and means for inductively coupling said output inductance to said secondary windin of said isolation transformer, and having a source connected in a current loop comprising a primary winding of said isolation transformer and input switching means for periodically closing said loop, and output switching means for connecting a junction between said output energy storage capacitance and said output inductance to said return current path for said load while said input switching means is in a condition to open said source current loop.

19. A switching power amplifier stage for producing an output voltage to a load comprised of two dc-to-dc converters with outputs connected to opposite ends of said load for parallel operation in a true push-pull mode from a single DC power source, each converter comprising an input inductance, a first energy storage capacitance, the primary winding of an isolation transformer, a return current path for said load, and bidirectional current means for periodically connecting a junction between said input inductance and said first energy storage capacitance to said return current path for said load, an output inductance, a secondary winding of an isolation transformer and a return current for said load, and bidirectional current switching means for alternately connecting a junction between said input inductance and first storage capacitance to said return current path for said source and a junction between said second storage capacitance and said output inductance to said return current path of said load, said switching means of one converter being 180°

out of phase with said switching means of the other converter, and in each converter separately, means for inductively coupling said input inductance to the primary winding, and said output inductance to the secondary winding of said isolation transformer.

20. A switching power amplifier stage as defined in claim 19 wherein for each converter the coupling coefficeints and turn ratios of said input inductance and primary winding and of said output inductance and secondary winding are selected for a matching condition n_i =k_i, and n_i is equal to the square root of the ratio of self inductance L_a, of said primary winding in one case and self inductance L_b of said secondary winding in the other case to the inductance L_i, where i is 1 to indicate input inductance L₁ for the matching condition of zero ripple in the input current from said source in one case, and i is 2 to indicate output inductance L₂ for the matching condition of zero ripple in the output current to said load in the other case.