Electricity: power supply or regulation systems – Input level responsive – Phase controlled switching using electronic tube or a three...
Reexamination Certificate
2000-02-18
2001-02-13
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Input level responsive
Phase controlled switching using electronic tube or a three...
C323S320000, C315S194000
Reexamination Certificate
active
06188214
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to an AC phase control switches used in lamp dimmers, and fan controls, and the like, and more particularly to an RFI inductor which can perform RFI filtering in a small, low heat dissipating package.
BACKGROUND OF THE INVENTION
The need for RFI suppression in phase controlled switches is well known in the prior art of phase control. Phase control switches with good RFI filtering tend to have bulky inductors in order to reduce heat dissipation and maintain adequate inductance. Phase controllers produce RFI frequencies during the step rise in current when the phase control switch is first activated. Typically an inductor is placed in series with the switch and a first capacitor is placed across the series combination. When the phase switch conducts, the inductor and capacitor form a resonant tank filter which has a break frequency which suppresses the RFI frequencies below a level which can cause interference with the AM broadcast band. This is well known in the prior art. A problem arises with attaining the maximum power control in the smallest package. When the phase controller is conducting and the load active, heat is dissipated by a first order phase switch voltage drop, and by a second order RFI inductor voltage drop. The RFI inductor must have many turns for the required inductance, and be of a large wire diameter to limit I
2
R loss in the inductor.
SUMMARY OF THE INVENTION
This invention reduces the I
2
R loss of a first inductor by reducing the number of winding turns carrying load current, and compensating for the loss of inductance by adding a second winding of small diameter wire on the first inductor core which resonates with a second filter capacitor. The second winding resonant circuit is chosen to resonate at a frequency point below the AM band, which at switch conduction resonates and causes a Q rise in flux in the second winding and shared inductor core. This produces a larger effective inductance in the load carrying inductor, which acts to limit the rate of rise of step current and the RFI frequencies generated. The bandwidth of the second winding resonant circuit is selected to be wide enough to start the RFI rejection below the AM broadcast band and extend to the resonant break frequency formed by the first filter capacitor and the load carrying inductor. In this way the heat dissipated by the inductor is much less and therefor the inductor can be of a smaller physical size.
This invention demonstrates a method to reduce the size of the inductor without sacrificing RFI suppression, allowing a smaller overall size of phase controller than the prior art.
DETAILED DESCRIPTION OF THE PRIOR ART
RFI Inductors used in phase controllers are typically large and bulky in respect to the package size of a controller, such as a light dimmer, for adequate suppression of RFI frequencies in the AM band. Much of the bulk comes from the wire diameter size, and number of turns required to limit the I
2
R heating from the inductor during the conduction period of the load. It is desired to have the smallest overall device size for a phase controller such as a dimmer. Heat dissipated inside the device limits the overall smallest size. An inductor with few turns of wire is desirable for a smaller inductor size, and less I
2
R loss, allowing a smaller overall phase controller package. In a conventional RFI filter such as shown in
FIG. 1
, reducing the turns on a given core
4
reduces the inductance to a value which will not sufficiently act as an RFI suppressor.
FIG. 1
is a typical circuit with a choke or inductor
2
having a winding
6
on a core
4
. The inductor
2
is connected in series with a phase control switch, such as a triac
8
, with a first filter capacitor
12
connected across the series combination of inductor
2
and triac
8
. The junction of inductor
2
and capacitor
12
connects to the hot power line
16
. The junction of triac
8
and capacitor
12
is connected to the load
10
, and the triac gate
9
is connected to a phase trigger control circuit
7
.
FIG. 2
shows the time waveform
21
for the step in current to the load, while waveform
22
shows the frequency spectrum response for the step in load current. When the triac
8
switches into conduction, inductor
2
slows the steep rise in current shown at
20
in
FIG. 2
, suppressing the bandwidth of frequencies generated by the step in current. Further filtering occurs at the break frequency formed by capacitor
12
resonating with inductor
2
generally shown at point
24
on frequency response
22
. For comparison purposes, the inductor
2
, which together with capacitor
12
, determines the frequency response
22
, has few turns
6
of large diameter wire and is of a small physical size with reduced I
2
R loss. The break frequency formed by capacitor
12
resonating with inductor
2
, is shown generally at
24
. Note that the response
22
is not suppressed below the desired suppression level
28
in the lower AM broadcast band
26
, from 550 kHz to about 600 kHz. Normally a much larger inductor with many more heat dissipating turns would be used to lower the break frequency below the AM band to avoid AM interference.
This invention describes a method which allows reduction of winding turns on the inductor, while lowering I
2
R loss, without sacrificing RFI suppression.
REFERENCES:
patent: 3484623 (1969-12-01), Cain
patent: 3919656 (1975-11-01), Sokal et al.
patent: 4538092 (1985-08-01), Goralnik
patent: 4876498 (1989-10-01), Luchaco et al.
patent: 4914327 (1990-04-01), Dekker
patent: 4954768 (1990-09-01), Luchaco et al.
patent: 4965509 (1990-10-01), Oldham
patent: 5179324 (1993-01-01), Audbert
patent: 5319301 (1994-06-01), Callahan et al.
patent: 5550440 (1996-08-01), Allison et al.
patent: 5629607 (1997-05-01), Callahan et al.
Pass & Seymour, Inc.
Riley Shawn
Wall Marjama & Bilinski
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