DC-to-DC switching converter

• US 4,184,197 A
• Filed: 09/28/1977
• Issued: 01/15/1980
• Est. Priority Date: 09/28/1977
• Status: Expired due to Term

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Middlebrook, Robert D., Cuk, Slobodan M.
• Primary Examiner(s): Shoop, William M.
• Application Number:
  US05/837,532
• Time in Patent Office: 839 Days
• Field of Search: 336/184, 363/15, 363/16, 363/20, 363/21, 363/40, 363/106, 363/110, 363/124, 363/131, 363/140
• 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

A dc-to-dc converter having nonpulsating input and output current uses two inductances, one in series with the input source, the other in series with the output load. An electrical energy transferring device with storage, namely storage capacitance, is used with suitable switching means between the inductances to DC level conversion. For isolation between the source and load, the capacitance may be divided into two capacitors coupled by a transformer, and for reducing ripple, the inductances may be coupled. With proper design of the coupling between the inductances, the current ripple can be reduced to zero at either the input or the output, or the reduction achievable in that way may be divided between the input and output.

Claims

1. A dc-to-dc converter having both input and output current nonpulsating for applying an input voltage from a source to a load, said converter being comprised of:

an input inductance,

storage capacitance,

an output inductance,

means connecting said input voltage source, said input inductance, said storage capacitance, said output inductance, and said load in series to form a series circuit, said series circuit having a junction between said input inductance and said storage capacitance, and a junction between said storage capacitance and said output inductance, and

switching means for alternately connecting the junction between said input inductance and said storage capacitance, and the junction between said storage capacitance and said output inductance, to return current paths for said source and load, whereby an improved dc-to-dc converter is provided which has optimum topolopy and superior performance properties.

2. A dc-to-dc converter as defined in claim 1 wherein said input inductance is a tapped inductor to form an autotransformer, and said switching means which previously connected the junction between said input inductance and said storage capacitance to the source return current path instead connects the inductor tap to the source return current path.

3. A dc-to-dc converter as defined in claim 1 wherein said output inductance is a tapped inductor to form an autotransformer, and said switching means which previously connected the junction between said output inductance and said storage capacitance to the load return current path instead connects the inductor tap to the load return current path.

4. A dc-to-dc converter as defined in claim 1 wherein said input and output inductances are respective first and second coupled inductors, whereby current ripples are reduced in at least one of two currents consisting of an input current through said first inductor and an output current through said second inductor.

5. A dc-to-dc converter as defined in claim 4 wherein said first and second inductors are coupled on a core to form a transformer designed for the condition n=k for zero output current ripple, where k is the coupling coefficient and n is equal to the square root of the ratio of the self inductances L₁₁ and L₂₂ of said first and second inductors, respectively.

6. A dc-to-dc converter as defined by claim 4 wherein said first and second inductors are coupled on a core to form a transformer designed for the condition n=1/k for zero input current ripple where k is the coupling coefficient and n is equal to the square root of the ratio of the self inductances L₁₁ and L₂₂ of said first and second inductors, respectively.

7. A dc-to-dc converter as defined in claim 4 wherein said first inductor is tapped to form an autotransformer, and said switching means which previously connected the junction between said first inductor and said storage capacitance to the source return current path instead connects the inductor tap to the source return current path.

8. A dc-to-dc converter as defined in claim 4 wherein said second inductor is tapped to form an autotransformer, and said switching means which previously connected the junction between said second inductor and said storage capacitance to the load return current path instead connects the inductor tap to the load return current path.

9. A dc-to-dc converter as defined in claim 1 wherein said switching means is comprised of a first semiconductor switch connecting the junction between said input inductance and said storage capacitance to said return current path for said source, and a second semiconductor switch connecting the junction between said output inductance and said storage capacitance to said return current path for said load, and means for alternately turning said switches on.

10. A dc-to-dc converter as defined in claim 9 wherein said first semiconductor switch is a bipolar power transistor and said second semiconductor switch is a diode.

11. A dc-to-dc converter as defined in claim 9, wherein said switches are VMOS power transistors in an arrangement in which complete symmetry and bidirectional energy flow are preserved.

12. A dc-to-dc converter as defined in claim 1 wherein said storage capacitance is divided into two capacitances, and said means for connecting in series said input voltage source, said input inductance, said two capacitances, said output inductance, and said load is comprised of an isolation transformer having a primary winding connected between one capacitance and said return current path for said source and having a secondary winding connected between the other capacitance and said return current path for said load.

13. A dc-to-dc converter as defined in claim 12 wherein said input and output inductances are comprised of first and second inductors coupled to reduce ripple in at least one of said input and output currents.

14. A dc-to-dc converter as defined in claim 12, and including at least one additional load, said isolation transformer having an additional secondary winding for the additional load and a separate storage capacitance and inductance in series coupling the additional secondary winding of said transformer to the additional load, and said switching means includes means for alternately connecting the junction between said separate inductance and storage capacitance to a return current path for said additional load.

15. A dc-to-dc converter as defined in claim 12 wherein said input and output inductances are comprised of an input inductor and a plurality of output inductors for a plurality of loads, and said input inductor is coupled to said plurality of output inductors to reduce ripple in at least one of said input and output currents.

16. A dc-to-dc converter as defined in claim 15 wherein said input inductor is tapped to form an autotransformer, and said switching means which previously connected the junction between said input inductance and said storage capacitance to the source return current path instead connects the inductor tap to the source return current path.

17. A dc-to-dc converter as defined in claim 15 wherein one of said output inductors is tapped to form an autotransformer, and said switching means which previously connected the junction between said output indutance and said storage capacitance to the load return current path instead connects the inductor tap to the load return current path.

18. A dc-to-dc converter as defined in claim 1 wherein said storage capacitance is divided into two capacitances and including an autotransformer having a plurality of taps, one connected to one of said two capacitances, one connected to the other of said two capacitances, one connected to said return current path for said source, and one connected to said return current path from said load, the taps for said storage capacitances and said return current paths being distinct.

19. A dc-to-dc converter as defined in claim 18, and including at least one additional load, said autotransformer having an additional tap for connection to a return current path for said additional load and a separate storage capacitance and inductance in series coupling a tap of said autotransformer to said load, and said switching means includes means for alternately connecting the junction between said separate inductance and storage capacitance to a return current path for said additional load.

20. A high efficiency dc-to-dc converter between a source of dc voltage and a load, said converter using two inductances, one in series with said source, the other in series with said load, and to obtain a dc level conversion, an energy storage capacitance and switching means for alternately connecting said storage capacitance between the source inductance and source return current path while simultaneously connecting the load inductance to the load return current path, and connecting said storage capacitance between the load inductance and the load return current path while simultaneously connecting the source inductance to the source return current path, whereby nonpulsating input and output current is provided.

21. A high efficiency dc-to-dc converter between a source of dc voltage and a load, said converter using two inductances, one a tapped inductor in series with said source, the other an inductor in series with said load, and to obtain a dc level conversion, an energy storage capacitance and switching means for alternately connecting said storage capacitance between the one inductor and source return current path while simultaneously connecting the other inductor to the load return current path, and connecting said storage capacitance between the other inductor and the load return current path while simultaneously connecting the tap of said one inductor to the source return current path.

22. A high efficiency dc-to-dc converter as defined in claim 21 wherein said two inductances are comprised of first and second coupled inductors, whereby current ripples are reduced in at least one of said input and output currents.

23. A high efficiency dc-to-dc converter between a source of dc voltage and a load, said converter using two inductances, one an inductor in series with said source, the other a tapped inductor in series with said load, and to obtain a dc level conversion, an energy storage capacitance and switching means for alternately connecting said storage capacitance between the one inductor and source return current path while simultaneously connecting the tap of the other inductor to the load return current path, and connecting said capacitance between the other inductor and the load return current path while simultaneously connecting said one inductor to the source return current path.

24. A high efficiency dc-to-dc converter as defined in claim 23 wherein said two inductances are comprised of first and second coupled inductors, whereby current ripples are reduced in at least one of said input and output currents.

25. A high efficiency dc-to-dc converter as defined in claim 24 wherein said two inductors are coupled to form a transformer designed for the condition n=k for zero output current ripple, where k is the coupling coefficient and n is equal to the square root of the ratio of the self inductances L₁₁ and L₂₂ of said first and second inductors, respectively.

26. A high efficiency dc-to-dc converter as defined in claim 24 wherein said two inductances are coupled to form a transformer designed for the condition n=1/k for zero input current ripple where k is the coupling coefficient and n is equal to the square root of the ratio of the self inductances L₁₁ and L₂₂ of said first and second inductors, respectively.

27. A high efficiency dc-to-dc converter coupling a source of DC voltage to a load, said converter being comprised of an isolation transformer having a primary winding, one end of which primary winding is connected in series sequence with a first storage capacitance and a first inductance to said source, and the other end of which primary winding is connected to the source return current path to form a primary series circuit, said primary series circuit having a junction between said first storage capacitance and said first inductance, and a secondary winding, one end of which secondary winding is connected in series sequence with a second storage capacitance and a second inductance to said load and the other end of which secondary winding is connected to the load return current path to form a secondary series circuit, said secondary series circuit having a junction between said second storage capacitance and said second inductance, and switching means for alternately connecting the junction between said first storage capacitance and said first inductance to said source return current path and connecting the junction between said second storage capacitance and said second inductance to said load return current path.

28. A high efficiency dc-to-dc converter as defined in claim 27 wherein said first inductance and said second inductance are inductively coupled, whereby current ripples are reduced in at least one of two currents consisting of input current through said first inductance and an output current through said second inductance.

29. A high efficiency dc-to-dc converter as defined in claim 27 including a plurality of loads and a plurality of secondary series circuits, wherein said second storage capacitance for each secondary series circuit is comprised of a separate storage capacitance and a separate load inductance, and including only one primary series circuit comprised of a capacitor common to all loads, said common capacitor being connected in series with one source inductance connected in series with said source, the separate storage capacitance for each load being connected in series with the separate load inductance for each load, and said transformer having a plurality of secondary windings, one secondary winding for each of said plurality of secondary series circuits.

30. A high efficiency dc-to-dc converter as defined in claim 28 wherein said first inductance connected in series with said source is a tapped inductor, and said switching means which previously connected the junction between said first inductance and said storage capacitance to the source return current path instead connects the inductor tap to the source return current path.

31. A high efficiency dc-to-dc converter as defined in claim 28 wherein said second inductance connected in series with said load is a tapped inductor, and said switching means which previously connected the junction between said second inductance and said storage capacitance to the load return current path instead connects the inductor tap to the load return current path.

32. A high efficiency dc-to-dc converter coupling a source of DC voltage to a plurality of loads, said converter being comprised of an autotransformer having a plurality of taps, two of which taps are selected for a primary winding, and pairs of which taps are selected for a plurality of secondary windings, one end of said primary winding being connected in series sequence with a first storage capacitance and a first inductance to said source and the other end of said primary winding being connected to the source return current path, said series circuit of the primary winding having a junction between said first storage capacitance and said first inductance, and one end of each secondary winding is connected in series sequence with a different storage capacitance and a different inductance to a different one of said loads and the other end of each secondary winding is connected to its load return current path, said series circuits of the secondary windings having junctions between said different storage capacitances and said different inductances, and switching means for alternately connecting the junction between said first storage capacitance and said first inductance to said source return current path and connecting the junctions between said different storage capacitances and said different inductances in unison to their load return current paths.

33. In a converter, a transformer of appropriate design having a first winding and second winding, each winding being excited by a separate and proportional pulsating voltage waveform, thereby to reduce ripple in the current into said first winding to zero, or to reduce ripple in the current into said second winding to zero, depending upon the matching conditions in the design of the transformer, said matching conditions being n=ak for zero ripple in said second winding and n=a/k for zero ripple in said first winding, where n is equal to positive √

L₁₁ /L₂₂, and L₁₁ and L₂₂ are self-inductances of the respective first and second windings, k is the coefficient of coupling between said first winding and said second winding, and a is a positive constant of proportionality greater than, less than or equal to unity.