Forward converter switching at zero current

• US 4,415,959 A
• Filed: 03/20/1981
• Issued: 11/15/1983
• Est. Priority Date: 03/20/1981
• Status: Expired due to Term

• Current Assignee: VLT Corporation One Riverwalk Place
• Original Assignee: Vicor Corporation
• Inventors: Vinciarelli, Patrizio
• Primary Examiner(s): BEHA JR, WILLIAM
• Application Number:
  US06/246,120
• Time in Patent Office: 970 Days
• Field of Search: 363/20, 363/25, 363/27, 363/28, 363/47, 363/48, 363/62, 363/131, 363/124, 323/282, 323/289, 323/351
• US Class Current: 363/21.04
• CPC Class Codes: H02M 3/33538 of the forward type H02M3/3353, H02M3/33569 take precedence
• 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

A DC-to-DC converter processes power by a sequence of energy transfer cycles in each of which a quantum of energy is taken from a voltage source towards a current sink via a magnetic energy storage device (specifically a transformer having a small effective leakage inductance) and a capacitor. This (effective) LC circuit defines a characteristic time scale for the rise and fall of the current drawn from the voltage source so that a switching device connected in series with the source can be switched on and off at essentially zero current. Following each cycle the energy stored in the capacitor is released by the current sink. After the capacitor is discharged, the sink current is carried by a rectifier diode connected in parallel with the capacitor. This prevents the LC circuit from becoming a resonant circuit and leads to a unidirectional flow of energy from source to load which optimizes the efficiency and power density of the conversion process.

Claims

1. A single-ended, zero current switching forward converter circuit comprising:

a voltage source;

a power transformer including a primary winding and a secondary winding, said power transformer being constructed to have an effective secondary leakage inductance L_2e ;

a switching device to selectively couple said voltage source across the primary winding of said power transformer;

a first unidirectional conducting device connected in series with said secondary winding and oriented to conduct during conduction by said switching device;

a capacitor of capacitance C connected in series with said secondary winding and said unidirectional conducting device;

control means for selectively closing and opening said switching device to transfer energy from said voltage source via the effective leakage inductance of said transformer to charge said capacitance during an energy transfer cycle having a characteristic time scale of π

√

L_2e C.

2. The converter circuit of claim 1 wherein said control means is further adapted for opening said switching device in response to cessation of conduction by said fist unidirectional conducting device.

3. The converter circuit of claim 1 wherein the primary and secondary windings of said transformer are wound on a common magnetic core, the secondary winding being separated from the primary winding by a dielectric spacer whose thickness is set to yield a desired value for the effective secondary leakage inductance L_2e of said transformer.

4. The converter circuit of claim 1 further adapted to accept a load and further comprising an inductor connected in series between said capacitance and the load to deliver current to the load.

5. The converter circuit of claim 4 further comprising a second unidirectional conducting device connected in parallel with said capacitance and oriented to avoid voltage reversal across said capacitance, to periodically deliver current to the load after said capacitance is discharged.

6. The converter of claim 5 wherein said control means includes sensory means for sensing the voltage across the load, wherein said control means operating in response to said sensing means maintains a substantially constant voltage across the load by varying the time during which current delivered to the load is conducted by said second unidirectional conducting device.

7. The converter circuit of claim 6 wherein said control means initiates conduction by said switching device periodically at times separated by a continuously variable time interval dependent upon the load.

8. The converter circuit of claim 6 wherein said control means initiates conduction by said switching device at times separated by a variable integer multiple of a fixed time interval in response to the load.

9. The converter circuit of claim 7 wherein said control means terminates conduction by said switching device in response to cessation of conduction by said first unidirectional conducting device.

10. The converter circuit of claim 9 wherein the primary and secondary windings of said transformer are wound on a common magnetic core, the primary winding being separated from the secondary winding by a dielectric spacer whose thickness is set to yield a desired value for the effective secondary leakage inductance L_2e of said transformer.

11. The converter circuit of claim 9 wherein said power transformer, incorporates an auxiliary discrete inductor to yield a desired value for the effective secondary leakage inductance L_2e of said transformer.

12. The converter circuit of claim 11 wherein said auxiliary inductor is connected in series with the primary winding of said transformer.

13. The converter circuit of claim 11 wherein said auxiliary inductor is connected in series with the secondary winding of said transformer.