Integrated transformer and inductor

• US 4,613,841 A
• Filed: 04/15/1985
• Issued: 09/23/1986
• Est. Priority Date: 11/30/1983
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Roberts, Victor D.
• Primary Examiner(s): Kozma, Thomas J.
• Application Number:
  US06/723,020
• Time in Patent Office: 526 Days
• Field of Search: 336/83, 336/84 R, 336/84 M, 336/65, 336/160, 336/165, 336/212, 336/178, 315/57, 315/62, 315/276, 315/282
• US Class Current: 336/83
• CPC Class Codes: H01F 17/043 with two, usually identical or nearly identical parts enclosing completely the coil (pot cores)
• CPC Class Codes: H01F 27/38 Auxiliary core members; Auxiliary coils or windings
• CPC Class Codes: H01F 38/08 High-leakage transformers or inductances
• CPC Class Codes: H01F 38/10 Ballasts, e.g. for discharge lamps
• CPC Class Codes: H05B 41/2822 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations

Abstract

An electrical transformer comprises a hollow form exhibiting high magnetic permeability and interior projections extending between separable halves of the form to provide a low magnetic leakage transformer core. Primary and secondary windings are disposed around the central projections. Furthermore, there is included means internal to the form for providing a lower permeability magnetic circuit shunt path. The internal shunt path means is typically either a cylinder or disc structure. A reduction in stray magnetic flux is desirable since it means that smaller, less expensive transformers may be constructed. The transformer of the present invention is particularly useful in electronic ballast circuits for gas discharge lamps because the magnetic shunt path acts as a current-limiting inductor. Moreover, since the transformers of the present invention do not generate external magnetic fields, flux shields are not required to maintain high efficiency.

Claims

1. An electrical transformer comprising:

a substantially closed hollow and substantially cylindrical form comprising high permeability magnetic material, said form being divided in the axial direction into two cup-shaped pieces having a flat bottom portion and rounded sides;

high permeability opposing projections extending inward from each of the flat portions of said forms, said projections abutting to form a closed magnetic circuit;

a primary electrical winding disposed about at least one of said projections;

a secondary electrical winding disposed about at least one of said projections; and

magnetic shunt means internal to said cylindrical form and disposed between said primary electrical winding and said secondary electrical winding for providing a lower permeability magnetic circuit shunt path, said magnetic shunt means comprising an internal cylindrical shell disposed about said projections and extending between said flat form portion.

2. The transformer of claim 1 in which said shell comprises material having lower magnetic permeability than said form.

3. The transformer of claim 1 in which said shell extends between said flat portions so as to provide at least one gap between said shell and at least one of said forms.

4. The transformer of claim 1 in which said secondary winding is disposed about said shell.

5. The transformer of claim 1 further including apertures in said form for external connection of said primary and secondary electrical windings.

6. An electrical ballast capable of performing as a transformer with a series inductor, for use with a gas discharge lamp to provide impedance matching and control of current supplied to said gas discharge lamp, said ballast comprising:

a substantially closed hollow form, comprising high magnetic permeability material, said form being divided into two pieces so as to define an interior region;

high permeability projections extending inward from each of said form pieces, said projections abutting to form a high permeability magnetic circuit;

a primary electrical winding disposed about at least one of said projections;

a secondary electrical winding disposed about at least one of said projections; and

magnetic shunt means internal to said form and disposed between said primary electrical winding and said secondary electrical winding for providing a lower permeability magnetic circuit shunt path than is provided by said form, said magnetic shunt means comprising an internal cylindrical shell disposed about said projections and extending between said form pieces, said magnetic shunt means helping to control current supplied to said gas discharge lamp.