International Business Machines Corporation

James H Spreen

John B Gillett

Kevin Robert Covi

William J Petrowsky

Walter S Duspiva

A method and apparatus for suppressing capacitive current in transformers is described. The winding of a transformer is constructed or modified into two substantially identical winding halves wired in a series aiding configuration. Two leads emanate from the center point of the winding, where the two halves are connected in series. This center point is at a constant potential throughout the switching cycle of the transformer. Suppression of the capacitive current in the input/output leads of the transformer is achieved by introducing common mode impedance into each lead and a corresponding center tap lead. The common mode impedance can be introduced in a variety of ways such as: running the pair of leads through a toroid, bead or sleeve of magnetic material; winding the leads on a magnetic toroid or rod; or using the magnetic core structure to introduce the impedance. Placement of any of these magnetic materials in substantial proximity to the lead pairs as arranged will suppress the capacitive current due to the coupling of the leads and the magnetic material.

Suppression of transformer capacitive current

The magnetic core of the transformer is an E--E shaped core. The primary winding of the transformer is divided into three substantially identical planar coils, each coil being wound on one of the three separate core posts. The coils are wired in series such that a current in the primary winding will induce substantially identical magnetic fluxes in the two outer core posts, and an opposite flux in the center post. The secondary of the transformer is formed by a contact plate and a conductor frame which provide conducting paths through the window regions of the E--E core. The bottom of the core is mounted in a recess in the conductor frame. Positioned within in the conductor frame are four rectifiers which make electrical connections to the secondary contact plate. When the transformer delivers power, the voltage on the primary winding will be divided 1/4 on each of the outer coils and 1/2 on the center coil post. During this time only two of the rectifiers will be conducting current. During freewheel times, with no primary voltage, the load current will divide evenly among the four rectifiers. During commutate intervals, between freewheel and on times, the voltage on the primary winding will divide evenly among the three coils. This novel transformer permits a switch mode power supply to supply more power while providing more even cooling.

Three coil bridge transformer

A transformer with a secondary structure formed in a figure 8 pattern. The secondary structure defines two conducting paths which each incorporate a rectifier and each encircle part of the core only once. The conducting paths overlap and cross only in the window region of the core. The design of the secondary structure allows for the mechanical connections to the transformer to be physically separated on opposite ends of the transformer assembly. This structure allows for alleviation of the connector congestion and provides better cooling and also permits shorter connections to the rectifiers.

Transformer/rectifier assembly with a figure eight secondary structure

The novel magnetic core structure of this invention provides a combination of large differential type inductance and some common mode type inductance while accommodating common mode dc current in two parallel planar conductors such as bus bars or printed circuit lands. This combination of desirable functions is accomplished by incorporating both gapped and ungapped magnetic flux paths into a single core structure. The core structure is composed of two outer posts, two inner posts, and four link segments. The two inner posts of the present core are located in the position of the center leg of a tradiational E--E core structure. Unlike a conventional E--E core, the structural arrangement of the two inner posts provides both a gapped and an ungapped magnetic flux path. The ungapped magnetic flux path travels in a figure eight pattern, encircling each of the windows of the E--E core in one of the loops of the figure eight. The gapped flux path is created by positioning the two inner posts so that is a gap between the two inner posts themselves, and gap between each of the inner posts and one of the adjacent link segments. The gapped flux path is a closed path which passes through the outer posts and directly between the link segments passing across the air gaps in the center legs. This gapped path does not pass through the inner core posts at all.

Gapped/ungapped magnetic core

A dual mold choke is provided to reduce both differential and common mode electromagnetic interference. Ferrite cores are placed around DC power bus bars providing an inductor limiting differential mode noise and creating a choke reducing common mode noise. The use of E-cores provides a simplified mechanical assembly while providing high levels of noise reduction. An air gap between the center legs of the cores prevents saturation of the choke.

Combined differential and common mode choke for a power supply

A transformer has a multi-turn magnetic core about a loop of conductor. A bridge transformer has one turn of the core about one half of the conductor loop and a second turn of the core about the other half of the conductor loop, and an electrical center tap connection to the loop between the two halves thereof. Embedded diodes connect the ends of the loop to an external circuit.

Transformer having plural-turn core

A regulated voltage electrical power system has a driving section and a driven section. The driving section includes a power transformer primary structure and a ripple current carrying, driving winding of a filter system for the smoothed outputs circuits of the power system, each of which includes a single turn, driven filter winding magnetically coupled to the driving winding by a multi-path core structure. Each driven filter winding links that part of the multi-path structure which corresponds in cross-sectional area to the relative ripple voltage imposed by the power transformer on it. The power transformer secondaries for the outputs of the power system are also of a single turn each, differing output voltages being achieved by provision of differing number of primary winding turns associated with the various outputs. Planar diodes and core gap-filling ferrite inserts are provided in the secondary winding structures.

Pluggable power system having magnetic flux coupled power transformer

A transformer structure includes two planar primary windings in a single plane with one primary winding on each leg of a core. The primary windings are connected in series or in parallel. The secondary structure includes a planar conductor structure about the core. A conductor passes through the core and makes electrical connection to the planar conductor through diode rectifiers. An anti-phase embodiment has dual primary circuits and dual cores with a combined secondary structure. Both plate-form and circuit card form embodiments are disclosed.

Plank and frame transformer

A d.c. to d.c. converter system converts a d.c. signal into a pulsating a.c. signal, which is applied to the primary of a power transformer. A transformer in which the primary and secondary windings are planar is employed to generate the output pulse signal. The planar transformer design provides the inductance required to filter the output signal and reduce the ripple therein, while simultaneously providing tight coupling between the primary and secondary windings. A single turn secondary winding is provided to reduce the number of turns in the transformer and thereby reduce the associated power loss.

D. C. to D. C. converter

A power supply circuit for producing at least one output which is essentially free from current ripple is disclosed. A chopped DC voltage source is applied to a transformer having a primary coil and at least two secondary coils. The secondary coils provide input voltages to output stages which each include a rectifier diode, a freewheeling diode and an LC filter. The inductors in the LC filter of adjacent output stages are magnetically coupled together. The characteristics of these inductors are selected such that the current ripple through the inductors in all the output stages, other than the first output stage, is essentially zero. Multiple inductors can also be employed in the first output stage with each one being magnetically coupled to the inductor in a different succeeding output stage. These multiple inductors in the first output stage can be combined in series or in parallel. A chained approach to coupling inductors as well as the use of an add-on ripple transformer can also be employed to product at least one essentially ripple-free output.

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Stone Ridge, NY, United States of America

James H Spreen