Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Transformer in the supply circuit
Reexamination Certificate
2000-03-14
2001-05-29
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Transformer in the supply circuit
C315S282000, C315S2090SC, C315S224000, C336S180000, C336S225000
Reexamination Certificate
active
06239557
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of transformers, and in particular to transformers used to provide high voltage for lamps.
2. Description of Related Art
FIG. 1
illustrates an example circuit diagram for an electronic ballast
100
, as might be used to provide a high-voltage, high-frequency signal for a cold cathode fluorescent lamp
110
from a relatively low-voltage DC supply signal Vin
120
. The controller
130
and switching devices
131
,
132
control the current flow through the transformers
140
,
150
, so as to provide the required current to the lamp
110
during the different stages (ignition, steady state, etc.) of the lamp's illumination.
The high-voltage transformation is provided by the step-up transformer
150
, which typically has a high turns ratio, such as 300:1, between the secondary
150
s
and primary
150
p
coils. The required high-frequency signal is provided by an LC resonant tank, wherein the transformer
140
form the resonant inductor, and the resonant capacitance is formed by shielding parasitic capacitances and the interwinding capacitance of transformer
150
. U.S. Pat. No. 5,495,405, “Inverter Circuit for Use with Discharge Tube”, issued Feb. 27, 1996 for Fujimura et al, teaches the use of the parasitic capacitance produced in the secondary side of the step up transformer as a component of the resonant circuit, and is incorporated by reference herein.
FIG. 2
illustrates an example embodiment of the step-up transformer
150
, as typically employed in a prior art electronic ballast
100
. Each of the coils
150
s
,
150
p
, and
150
a
are wound by rotating a hollow core bobbin
250
in a direction
210
, while a wire is wound around the bobbin
250
and laid upon sections of the bobbin
250
in the illustrated winding direction
220
. The wires may be wrapped around a common segmented bobbin, or wrapped around individual bobbin segments that are subsequently bonded together to form the segmented bobbin. After the appropriate number of turns of wire are laid upon the bobbin
250
, the wire ends of each coil
150
s
,
150
p
, and
150
a
are made available for connection to the other components of the electronic ballast
100
of FIG.
1
. In order to maintain the appropriate coil phases indicated by the “dot” phase convention of each coil
150
s
,
150
p
,
150
a
of
FIG. 1
, the ends of each coil are arranged as discussed below and as indicated by the two alternative node assignments of FIG.
2
. If the starting (right) end of the secondary coil
150
s
is assigned to node
2
(and therefore the terminating (left) end of the secondary coil
150
s
is assigned to node
4
), then node
1
must be assigned to the starting (right) end of the primary coil
150
p
and node
3
to the terminating (left) end, in order for the primary
150
p
and secondary
150
s
coils to have the dot-phase relationship indicated in FIG.
1
. In like manner, based on the choice of node
2
as the starting end of the secondary coil
150
s
, node
6
must be assigned to the start (right) end of the auxiliary coil
150
a
, and node
8
to the terminating (left) end, in order to maintain the proper phase relationship between the auxiliary coil
150
a
and the secondary coil
150
s
. Alternatively, as indicated by the parenthesized node assignments, if node
4
is assigned to the start (right) end of the secondary coil
150
s
, then node
3
must be assigned to the start (right) end of the primary coil
150
p
, and node
8
must be assigned to the start (right) end of the auxiliary coil
150
a
. As would be evident to one of ordinary skill in the art, the bobbin rotation direction
210
may be reversed, and the winding direction
220
may be reversed.
Coils
150
a
,
150
p
, and
150
s
are inductively coupled by their proximity and relationship to each other. The inductive coupling may be increased by providing a ferrite core within the center of the bobbin
250
that traverses the length of the transformer
150
. Unfortunately, the proximity and relationship of coils
150
p
and
150
s
also introduces a capacitive coupling between these coils
150
p
and
150
s
. This capacitive coupling adversely affects the circuit operation of the electronic ballast
100
, and severely limits the voltage gain of the step-up transformer
150
.
BRIEF SUMMARY OF THE INVENTION
It is an object of this invention to provide a ballast having a high efficiency. It is a further object of this invention to provide a high efficiency high-gain transformer suitable for use in an electronic ballast. It is a further object of this invention to provide a method of winding a transformer that increases the transformer's efficiency.
These objects and others are achieved by providing a method of winding a step-up transformer that substantially minimizes the parasitic capacitance effects between the primary coil of the transformer and the secondary coil of the transformer. The primary coil is wound around a sectional bobbin and laid upon the bobbin in a winding direction that is opposite to the winding direction of the secondary coil. The opposite winding directions allow the high-voltage terminal ends of the primary and secondary coils to be maximally separated. The maximal separation of high-voltage signals within each coil reduces the effects of the capacitive coupling between the coils, and also maximizes the breakdown voltage between the coils. In a preferred embodiment, the auxiliary coil of the step-up transformer is also configured to minimize the effects of capacitive coupling and to maximize the breakdown voltage among the coils.
REFERENCES:
patent: 4274136 (1981-06-01), Onodera et al.
patent: 4449111 (1984-05-01), Nakajima
patent: 4514712 (1985-04-01), Mc Dougal
patent: 5418513 (1995-05-01), Fujisawa et al.
patent: 5495405 (1996-02-01), Fujimura et al.
patent: 5615091 (1997-03-01), Palatnik
patent: 5959412 (1999-09-01), Ushijima
Chang Chin
Himman Roderick T.
Philips Electronics North America Corporation
Philogene Haissa
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