US 4,994,952 A · Low-noise switching power supply having variable reluctance transformer

Abstract

There is provided a low-noise switching power supply for producing a regulated output voltage from an unregulated supply. The power supply includes a main transformer having first, second and third legs. A primary winding associated with a first leg produces an alternating magnetic flux in the core. A load winding associated with a second leg produces the output voltage from the power supply. A control winding is associated with the third leg. The regulated output voltage is compared to a reference voltage and used to operate a control circuit which alternately short circuits the control winding so as to vary the reluctance pass in the transformer and maintain the output voltage at a substantially constant predetermined value. A feedback circuit including a coupling transformer connects the primary coil to the switching circuit to improve regulation and provide a "soft start" capability. A second embodiment of the present invention utilizes a constant frequency source to drive the main switching transistors of the unregulated power supply instead of the self oscillating scheme.

Claims11

Dependent claims

A low noise switching power supply for producing a regulated output voltage from an unregulated supply to a load, comprising:

(a) a transformer including:
i. a transformer core including first, second and third core legs;
ii. a set of transformer windings associated with said transformer including:
a. a control winding associated with said first core leg;
b. a primary winding associated with said second core leg;
and
c. a load winding associated with said third core leg for producing said output voltage;
and
(b) control means for controlling said output voltage comprising:
i. switching means responsive to said unregulated supply for providing an oscillating voltage of substantially constant frequency to said primary winding;
ii. means for comparing the actual output voltage produced at said load winding with a reference representative of the desired output voltage value to produce an error signal representative of the difference between said actual output voltage and said reference;
and
iii. means responsive to said error signal for short circuiting said control winding as required to maintain said output voltage at said desired value.

10 more elements

A constant frequency switching power supply for producing a regulated output voltage from an unregulated supply to a load, comprising:

(a) a transformer including:
i. a transformer core including first, second and third core legs;
and
ii. a set of transformer windings associated with said transformer including:
a. a control winding associated with said first core leg;
b. a primary winding associated with said second core leg;
and
c. a load winding associated with said third core leg;
and
(b) control means for controlling said output voltage comprising:
i. a constant frequency source applied to a pair of switching transistors in said unregulated supply for providing an oscillating voltage of substantially constant frequency to said primary winding independent of the load winding;
ii. means for comparing the actual output voltage produced at said load winding with a reference representative of the desired output voltage value to produce an error signal representative of the difference between said actual output voltage and said reference;
and
iii. means responsive to said error signal for short circuiting said control winding as required to maintain said output voltage at said desired value.

11 more elements

Dependencies are inferred from the claim text.

Low-noise switching power supply having variable reluctance transformer

Life of this patent

Low-noise switching power supply having variable reluctance transformer

Life of this patent

Abstract

Claims11