Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2001-10-16
2004-01-06
Riley, Shawn (Department: 2838)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C336S155000
Reexamination Certificate
active
06674320
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a variable inductor. More particularly, the present invention relates to an apparatus and method for orthogonal inductance variation.
BACKGROUND OF THE INVENTION
Inductors possess the ability to store energy in their electromagnetic fields. This property has made inductors an important component in several categories of electrical circuits. As an example, inductors are important components in power conversion equipment, oscillators, and filters. In power conversion equipment, inductors are used in circuits which provide voltage rectification. Also, inductors are used in a variety of electrical devices such as voltage controlled oscillators, amplifiers, modulators, tuning circuits, and filters. In these and other embodiments, the natural resonant frequency of an oscillator or the cut-off frequency of a filter is determined, in part, by the combination of capacitors and inductors used in those circuits. In some instances, inductor inductance can be intentionally varied such as by mechanically changing the physical size of the core air gap. However, these mechanical methods have drawbacks such as the need for additional parts, complexity and bulk.
The inductors in these tunable devices have long been considered static inductance inductors, and this mindset has stifled growth and improvement in many electronics devices. This is particularly true of low voltage and high current power conversion devices. In one particular example, the demand for higher performance, microcontroller-based products for use in communication and processing applications continues to increase rapidly. As a result, microcontroller-based product manufacturers are requiring the components and devices within these products to be continually improved to meet the design requirements of a myriad of emerging audio, video and imaging applications. Microcontroller's are being designed with increasingly higher load demands and with lower voltage requirements. For example, many microprocessors are now designed to operate with a 3V power supply, and others are designed to work with less than a 1V power supply. This trend towards designing integrated circuits to operate at lower voltage levels is likely to continue. However, efficient power converters are increasingly difficult to design at these lower voltage levels.
Generally, AC power is converted to a steady DC power supply for microcontroller use. Furthermore, DC power is transformed from one voltage level to another through power converters. High efficiency power conversion is increasingly difficult to achieve as power converter output voltage requirements decrease and load current demands increase. This difficulty is largely due to the dominant conductive and switching losses of the output rectifiers. In prior efforts to improve the efficiency of the power conversion, standard rectifier diodes were replaced with synchronous field effect transistor (“FET”) rectifiers. These FET based systems, also known as synchronous forward converter's (“SFC”), are inefficient at low voltages with high current, and when output voltages on the order of 1 Volt or less are desired, a better rectification method is needed.
An exemplary integrated circuit device using a non-variable inductor may, for example, include a synchronous FET rectifier. Synchronous FET rectifiers are used, for example, in a synchronous forward converter system
100
, as shown in FIG.
1
. SFC system
100
has a power source
102
and a load
116
. SFC system
100
also has a transformer
104
with a secondary winding
122
, a reset winding
123
and a transformer reset diode
106
. SFC system
100
also includes a primary switch
108
, an output rectifier switch
110
, a freewheeling rectifier switch
111
, an output inductor
112
, output capacitance
114
, and a feedback control circuit
118
. In typical operation, source
102
is a DC power source providing DC source voltage to the transformer
104
. Alternating ON and OFF states provided by controller
118
and primary switch
108
result in the generation of AC voltage. FET switches
108
,
110
, and
111
are synchronized by controller
118
.
During an “ON” state, primary switch
108
and output rectifier switch
110
are both configured to be on while the freewheeling switch
111
is configured to be off. During the ON state, voltage on secondary winding
122
of transformer
104
produces a positive voltage proportional to the primary side voltage. This voltage is a function of the turns ratio of transformer
104
. During the ON state the secondary winding
122
voltage minus the steady state load
116
voltage is applied across the inductor
112
. This results in a linear increase of current in inductor
112
.
During an “OFF” state, primary switch
108
and output rectifier switch
110
are configured to be off while the freewheeling switch
111
is configured to be on. Under this condition, magnetic forces within transformer
104
force the voltages on all windings to reverse polarity. These magnetic forces in conjunction with reset diode
106
facilitate reset of the transformer core to prevent saturation of the core material and subsequent loss of efficient transformer action. Because rectifier switch
110
is in the OFF state, the secondary winding
122
voltage is allowed to produce a negative potential in order to facilitate transformer
104
reset, without impacting power delivery to the load. Because freewheeling switch
111
is in the ON state, node
120
is coupled to the ground potential. This results in maintenance of current flow direction in output inductor
112
. During the OFF state the equivalent voltage across the inductor
112
is 0 minus the load
116
voltage resulting in a linear decrease of current in output inductor
112
.
The voltage and current ripple produced by the linear ramping of current in output inductor
112
is filtered by output capacitor
114
to produce DC current to load
116
. In this manner, output rectifier switches
110
and
111
are synchronized with the operation of primary switch
108
; however, this synchronization is a significantly complicated task. Accordingly, a need exists for a less complex method of operating a forward converter.
The average voltage value supplied to the load may also be regulated by SFC system
100
by varying the duty cycle with feedback control device
118
. For example, device
118
can vary the percentage of time that the positive voltage is provided to the input node
120
of output inductor
112
, in other words, changing the amount of time the power to the load is “off”. Reducing the duty cycle, reduces the DC voltage at the load and thus regulates the output voltage. The steady state transfer relationship for the forward topology is:
V
o
u
t
=
V
i
n
D
N
s
N
p
(
1
)
Where:
Np=Transformer Primary # of Turns
Ns=Transformer Secondary # of Turns
SFC system
100
is inefficient at low voltages with high current. Furthermore, increasing the number of rectifiers to parallel the equivalent resistance results in diminishing returns due to
1
2
CV
2
and gate drive current losses. These energy losses are expensive, give rise to increased heat generation/removal issues, and impact the reliability of the device due to increased possibility of burn out of the rectifier. When SFC system
100
is operated at low voltage and high current, the bulk of the loss is concentrated in conducted and switching loss within the output rectifiers
110
and
111
. Due to the placement of output rectifiers
110
and
111
, current flows through one of the two devices at all times, and all current that reaches load
116
flows through these devices. The losses can be significant, and a need exists for an efficient rectifier which can regulate output voltage and can do so without the high power losses of the prior art.
Demand also exists for efficient and/or smaller power
Duffy Thomas P.
Trivedi Malay
Zhang Yi
Primarion, Inc.
Riley Shawn
Snell & Wilmer L.L.P.
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