Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
1999-05-10
2001-06-05
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C361S256000, C431S258000
Reexamination Certificate
active
06242866
ABSTRACT:
The present invention relates to an electric gas-lighter, which may be applied, for example, to the cooking range of a gas cooker.
BACKGROUND OF THE INVENTION
Many known modern cooking ranges feature a built-in electric gas-lighter, which is operated manually
64
means of a pushbutton to produce a spark to light the flame.
The most commonly-used ranges with built-in electric gas-lighters are of the type indicated by
1
in
FIG. 1
, which comprises four gas burners
2
arranged in a square and each flanked by a respective ceramic-coated electrode
3
. Electrodes
3
define two pairs of output terminals of an electric gas-lighter
4
shown schematically and only as regards the output circuit. When operated, gas-lighter
4
generates a spark between each electrode
3
and the outer body (grounded together with the entire metal surface of the range) of the corresponding burner
2
; and the spark lights the flame of the burner/s 2 supplied with gas.
FIG. 2
shows a complete circuit diagram of a known type of gas-lighter
4
.
In addition to electrodes
3
, gas-lighter
4
comprises a first and a second input terminal
7
,
8
connected to a supply line (not shown); and a current-discharge generating circuit
5
interposed between input terminals
7
,
8
and electrodes
3
, and for producing the sparks on electrodes
3
.
Circuit
5
comprises an input resistor
9
connected to terminal
7
; and a rectifying diode
10
having the anode connected to resistor
9
, and the cathode connected to a first intermediate node
11
.
Circuit
5
also comprises a discharge capacitor
12
located between first intermediate node
11
and a second intermediate node
13
shortcircuited with second input terminal
8
; a known voltage discharger
15
(e.g. a Sidac high-energy, solid-state gas tube) parallel with the branch defined by capacitor
12
; and, in series with discharger
15
, the primary winding
16
of a transformer
17
. Transformer
17
also comprises two identical secondary windings
18
, each having far more turns than primary winding
16
, and the terminals of each of which have a pair of electrodes
3
of the type described above.
Gas-lighter
4
operates as follows.
When the gas-lighter
4
circuit is connected to the supply line, an initial transient state occurs in which capacitor
12
is charged to a threshold voltage value V
TH
equal to the ignition threshold value of discharger
15
, after which, a discharge current Isc of extremely high intensity (e.g. 150-280 A) flows along a discharge path extending through primary winding
16
of transformer
17
and terminating at capacitor
12
. At the terminals of primary winding
16
, a discharge voltage V1 (e.g. of 400 V) is generated during the discharge transient (lasting a few microseconds) and induces, at the terminals of secondary windings
18
, a discharge voltage V2 much higher than V1 (e.g. 28 kV); and, for each secondary winding
18
, voltage V2 is sufficient to produce a spark between each electrode
3
and the outer body of respective burner
2
, which is accompanied by instantaneous current flow between the two burners
2
of each pair of electrodes
3
, and through the metal surface of cooking range
1
.
Gas-lighters
4
of the above type have the drawback of generating, during the discharge transient producing the sparks, severe electromagnetic noise above the limits laid down by European standards (EN55014 and following).
FIG. 3
shows the result of an electromagnetic compatibility test to determine the voltage value between input terminals
7
and
8
during the discharge transient. The voltage values, expressed in dB&mgr;V, are measured in the 0.15 to 30 MHz frequency range; the regular, substantially horizontal line in the graph indicates the prescribed voltage limit, and the jagged line the measured voltage, which, as can be seen, exceeds the limit over the entire frequency range considered.
One proposed solution to the problem is to fit gas-lighter
4
with an electronic filter to reduce the electromagnetic noise during the discharge transient and so obtain a low-noise gas-lighter
4
a
as shown in FIG.
4
. Gas-lighter
4
a
comprises an electronic filter
20
interposed between terminals
7
,
8
and a circuit
5
a
equivalent to circuit
5
but having no resistor
9
. Filter
20
comprises two capacitors
21
a
and
21
b
located between a node
22
connected to the anode of diode
10
, and a node
23
shortcircuited with node
13
. More specifically, capacitors
21
a
and
21
b
are located between respective nodes
22
and
23
and a common node
24
which is the ground. Filter
20
also comprises a pair of decoupling resistors
25
towards the mains, a first of which is located between input terminal
7
and node
22
, and a second of which is located between input terminal
8
and node
23
. Filter
20
defines a preferential path by which to discharge the energy produced during the transient state. More specifically, said energy is conveyed by capacitors
21
a
and
21
b
directly towards ground to reduce the electromagnetic emissions emitted by the circuit.
Though filter
20
indeed provides for reducing the noise level generated during operation to well below the prescribed limit, gas-lighter
4
a
fitted with filter
20
is not without further drawbacks.
First, the ground connection of capacitors
21
a
and
21
b
may result in the entry into the gas-lighter
4
a
circuit of electromagnetic noise generated by other electric devices and traveling along the ground lines, or of the discharge energy at electrodes
3
. Second, though minimum for each gas-lighter
4
a
, the expense of providing a ground cable is far from negligible on a mass-production scale, as in the household appliance industry.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electric gas-lighter which is highly straightforward, and which provides for eliminating the drawbacks associated with gas-lighters of the type described above.
According to the present invention, an electric gas-lighter comprises a filter interposed between a pair of input terminals and a current discharge generating circuit for generating current discharges and cooperating with at least one input terminal to generate sparks as a consequence of the generation of the current discharges. The filter has no circuit elements connected to a reference potential, advantageously eliminating ground connections to simplify construction.
REFERENCES:
patent: 3824432 (1974-07-01), Gersing
patent: 4329628 (1982-05-01), Bohan, Jr.
patent: 4626196 (1986-12-01), Stohrer, Jr.
patent: 5267849 (1993-12-01), Paciorek
patent: 0 167 510 (1986-01-01), None
patent: 0 801 267 (1997-10-01), None
patent: 957315A2 (1999-11-01), None
patent: 1 551 728 (1979-08-01), None
patent: 1 175 160 (1987-07-01), None
Alemu Ephrem
Lowe Hauptman Gilman & Berner
Miller Europe S.p.A.
Wong Don
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