Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
9645~
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ELECTRONIC INSECT KILLER
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BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to devices for killing
insects by electrocution and, more particularly, to a device
of electronic character for killing insects by electrocution.
It has heretofcre been known to utilize AC voltage for
killing insects by applying the voltage across spaced
electrodes and with the insects being attracted toward the
electrodes by fluorescent lighting.
lS For this purpose, devices have been sold commercially
which employ simple step-up transformers for stepping up
conventional 60 Hertz AC line voltage to a level suitable
for electrocuting insects which come into contact or close
proximity to electrodes across wh$ch the 60 Hertz higher
voltage i9 present. To provide sufficient current for
this, the transformer is required to be large, bulky,
clumsy and expensive.
Moreover, in practice a very high failure rate has
occurred with such transformers. The failure mode resulting
in a failure rate is not well understood but is believed to
result in part from high temperature causing dielectric
breakdown and in part because of the transmigration of the
.
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winding elements (e.g., copper) to the opposite ends of the
tran~former core, possibly the result of corona which is
characteristic of such transformers. The transmigration
of elemental constituents eventually causes shorting of
the turns. But regardless of the reasons for such frequent
failure, it is undesirable and has caused conventional
insect electrocuters to be less commercially successful than
would otherwise be the case.
A further disadvantage of the use of such simple trans-
formers for stepping up the 60 Hertz AC line voltage isthat voltage regulating devices must be connected across
- the secondary winding to prevent extensive voltage variations
which could cause arcing between electrodes and which can
result from poor transformer voltage tolerances. Also, high
voltage variations could preclude obtaining safety certific-
ation of such devices by testing and certification agencies
such as Underwriters' Laboratories, Inc.
A related shortcoming of these prior art electrocuters
is that, due to size limitations and current output restrictions
2~0 at 60 ~ertz which are necessitated by such certification,
the electrocuter may be electrically overloaded or shorted
by insect carcasses clinging to the elctrodes since typically
electrocuters have lacked sufficient power to carbonize
the carcasses. Hence, these prior art devices sometimes
clog with dead insects. Short circuit protection is re-
quired in prior art devices to protect against damage to
the transformer from such shorting of the electrodes.
As noted, fluorescent lighting has been used in prior
art electrocuters to attract insects. The fluorescent lamps
have required the use of lamp ballasts which are known to be
space-consuming, heavy, and expensive. The ballasts also
generate heat which may contribute to the failure of other
components in the electrocuters, such as the above-mentioned
step-up transformers.
Such problems of the prior art have been long outstanding
and have remained unsolved.
649
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An object of the invention is the provision of a devi~e
for killing of insects by electrocution, which device is
electronic.
A further object of the invention is the provision of
such an electronic insect killer which utilizes a high
efficiency, compact, low cost, high power, reliable, and
lightweight solid state ciccuit.
Another object of the invention is the provision of
such an electronic insect killer which is not prone to
O electrical failure, clogging by insects or self-destruction
by short circuiting.
Yet another object of the invention is the provision
of such an electronic insect killer including such a solid
state circuit which not only develops high voltage for
insect electrocution but also produces lower voltage for
energizing fluorescent lamp means to attract insects toward
the electrodes.
Yet another object of the invention is the provision
of such an electronic insect killer including solid state
'O circuitry for energizing such fluorescent lamp means without
ballasting.
A still further object of the invention is the provision
of such an electronic insect killer which develops sufficient
electrical enerqy for carbonizing insects to avoid clogging,
overloading, short circuiting of electrodes, etc. by insect
carcasses.
A further object of the invention is the provision of
such an electronic insect killer which develops such high
electrical energy without compromising safety.
Yet another object of the invention is the provision
of such an electronic insect killer which is self-regulating
and is by design self-protected against short circuiting.
Still another object of the invention is the provision
of such an electronic insect killer which utilizes electrically
efficient components which develop relatively little heat.
49
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Among still other Qhjects of the inYentlon may he
noted the prov~si`on of such an electron~c i`nsect ki`ller
whi.ch.conduces to economical mas:s produc~ion, sim~l.e
ass:embly, facï:le repa~r, whi`ch.i`s si~ple and effectï.ve in
desi.gn, and whïch kïlls flies, mosqui.tos and myriad other
species of various flying insects.
Broadly, thos.e o~jects are attained hy the invention
which contemplates an electronic insect killer whi.ch comprises
a plurality of spaced electrodes adapted to be electrically
contacted by th.e bodies of insects, means for attracting
insects toward the.electrodes comprising at least one
fluorescent lamp, and solid state circuitry interconnected
with the electrodes and also with the lamp for providing
both a high voltage and a lower voltage at a high AC
frequency, with the high voltage ~eing supplied aaross the
electrodes and with the lower voltage ~eing supplied to
the lamp for ~allast-free energization of the lamp, and with
the high voltage being DC.
649
BRIEF DESCRIPTION OF THE DRAWINGS
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FIGURE 1 is a perspective view of an electronic insect
killer constructed in àccordance with and embodying the
present invention.
FIGURE 2 is a front vertical elevation of the electronic
insect killer of FIGURE 1 with a top of the device being
broken away in part to show electronic circuit components.
FIGURE 3 i5 a front vertical elevation with certain
grid-like cover and electrode elements removed.
FIGURE 4 iS a horizontal transverse cross-sectional
view taken generally along line 4--4 of FIGURE 2.
FIGURE 5 iS a schematic circuit diagram of electronic
circuitry of the new electronic insect killer.
FIGURE 6 iS a schematic circuit diagram of alternative
electronic circuitry of the new electronic insect killer.
FIGURE 7 is a schematic circuit diagram of electronic
circuitry which may be substituted for certain components
of the circuitry of FIGUR~ 6.
Corresponding reference characters indicate corresponding
parts throughout the several views of the drawings.
1. :ltj'3649
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DESCRIPTION OF T~E PREPERRED EMBODIMENTS
Referring now to FIGURES 1 - 4, a new insect killer
of the invention is designated genexally at 11. The new
device comprises a metal ba~e 13, e.g., of formed sheet
S metal~ Secured to and extending upwardly from base 13 is
an upstanding protective housing 15. Housing 15 is of
rectangular tubular configuration and constructed of
perforated sheet metal to provide grid-like front and rear
panels 17, 19 and side panels 21, 23. The perforations
may each typically be about one-half inch square.
Referring to FIGURE 2, extending across the top of
housing 15 is an inner cover 25 for closing the upper end
of housing 15 and which cover may simply be a single
rectangular piece of sheet metal having a downwardly turned
flange 27 extending around its periphexy.
Secured, as by sheet metal screws 29 threaded to flange
27, is an outer cover 31 of truncated pyramidic configuration
and also formed of sheet metal. A flat upper surface 33
of the cover is provided with a metal ring 35 for permitting
the new insect killer to be suspended, as in a stable or
commerical establishment, above ground level. Alternatively,
it may be supported by its base 1~ upon sny suitable surface.
Referring to FIGURES 3 and 4, there is contained within
cover closely spaced, concentric outer and inner grid-like
electrodes 37, 39, respectively, which may be referred as
grids. Each has me~h-like character and is of rectangular
form, with the mesh spacing being preferably about one-half
inch in both vertical and horizontal directions, the outer
and inner grids having also about one-half inch spacing
betwen them. Grids 37, 39 are supported top and bottom by
electrically insulating stand-offs or supports 41 in spaced
relation to base 13 and inner cover 25. Said grids 37, 39
are adapted to establish high-voltage electrical contact
with the bodies of insects for electrocution of such insects.
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It should be understood that the inqect~ may not actually
contact either of grids 37, 39 but instead may simply
induce an arc from one grid and through the insect body
toward the other grid.
Insects are attracted toward grids 37, 39 and fly
through the perforate openings of housing 15 in response
to W (ultraviolet) or so-called "black" light produced
by a pair 43, 45 of fluorescent lamps of tubular U-con-
figuration and l~cated centrally within inner grid 37.
Lamps 43, 45 are each of U-shaped configuration with each
having its ends terminating side-by-side, and plugged into
respective sockets 47, 49 on the under surface of the inner
cover 25. A metal support 51 extending downwardly from
cover 25 includes spring clips as shown at 53 which secure
the bend portions of each of lamps 43, 45.
Referring now to FIGURE 5, circuitry of the new
electronic insect killer is illustrated, being generally
designated 55. Said circuitry is mounted upon a circuit
board 57 (FIGURE 2) which is mounted upon inner cover 25
by standoffs 59.
~C line voltage at typically 120 VRMS powers the new
circuitry, being provided by a plug PLl to a full wave
diode rectifier bridge comprising diodes Dl - D4. Pul-
sating DC output of the bridge is filtered by a capacitor
Cl. A further capacitor C4 filters high frequency com-
ponents from the power supply to prevent introducing noise
to the AC line. The lower side of capacitor Cl is connected
to the junction of commonly connected emitters of a pair
of NPN transistors Ql, Q2, each having its collector
connected to one end of a transformer primary winding section
PRl, PR2. The center tap between the latter is connected
to the upper side of capacitor Cl.
Said primary windings form part of a transformer Tl
having a toroidal core 61 of a ferrite material. Also
wound upon said core are further primary windings in the
form of two sections PR3, PR4 with a center tap between
them connected also to the commonly connected emitters of
transistors Ql, Q2. The ends of the upper sections are
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connected through respective resistors Rl, R2, each shunt~d
by respective capacitors C2, C3, to the bases of transistors
Ql, Q2. Connected between the base of these two transistors
is a small saturating inductor SRl having a toroidal core
63. A diode D5 between the commonly connected emitters of
the transistors and one side of primary winding center tap
is provided for circuit starting purposes. Also a thermistor
R3 is provided for providing a bias voltage to the bases of
the transistors to initiate conduction of either Ql or Q2.
Said thermistor is of the type having a positive temperature
coefficient of resistivity. Thus, bias current will fall
off rapidly upon heating. Diodes D6, D7 are connected
across the emitter-collector terminals of the transistors
to prevent excessive reverse bias voltages at the collectors
of the transistors.
Sections PRl, PR2 are adpated to be alternately
energized current developed from the DC voltage across
capacitor Cl in response to high frequencies alternate
conduction of transistors Ql, Q2, which are.seen to be
connected by push-pull, inverter configuration.
~rimary winding sections PR3, PR4 generate feedback
voltages, in response to the alternating field generated
by energization of winding sections PRl, PR2, which are
provided through resistors Rl, R2. The latter limit the
current which may flow in response to said feedback
voltages but provides sufficient current for base drive
for alternate conduction of transistors Ql, Q2. Capacitors
C2, C3 are preferably utilized for.providing more rapid
switching of the conductive state of the respective
transistors Ql, Q2.
Saturating inductor SRl is utilized to control the
base voltages for transiqtors Ql, Q2. More specifically,
transistor Ql is initially rendered conductive by a base
current Ib = (PR4) - Vbe, where (PR4) is the voltage
R2
developed across primary winding section PR4, transistor
Q2 being biased off by the reverse voltage developed
across winding PR3 applied to resistor Rl. Voltage across
649
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the saturating inductor SRl is initially of a value
Vab = (PR3) + Vbe, where (PR3) is the voltage dèveloped
across primary winding section PR3. As the saturable
reactor reaches core saturation, Vab collapses robbing
transistor Ql of its base drive. The field of trans-
fonner T1 thereafter collapses, reversing the voltage
across the feedback winds PR3, PR4 and driving transistor
Q2 into conduction as soon as saturable reactor SRl
comes out of saturation, such process repeating at a
frequency which preferably is at least 4kHz and more
preferably about 20 kHz.
A secondary winding Xl of transformer Tl, which may
be numerous turns of conductor, which is pyramid wound
and impregnated, is 3dapted to provide high voltage, e.g.,
about 5,000 VRMS at a current of 20 mA. This high AC
voltage is provided by leads 65, 65' to the respective
outer and inner grid-form electrodes37, 39, there being
no fusing, voltage regulating devices or the like
connected across ~uch lead~ 65, 65' as the same are not
nece~ary in the new circUit.
~ ransformer ~1 is also provided with a plurality of
high reactance, i.e., relatively loosely coupled,secondary
win~8, including a secondary winding having three sections
X2, X3, and X4, as well as a further winding X5, with the
latter two winding sections X2 and X5 each adapted to
develop about three and one-half VRMS at approximately
one-half ampere, and with section X4 developing about
twice the latter voltage. Winding section X3 preferably
provides a potential of about 200 VRMS at nearly one-half
ampere under load conditions for energization of
fluorescent lamps 43, 45 with approximately 100 VRMS
across each.
Lamp 43 i~ seen to have a filament 67 at one end
which is connected across winding section X2. A filament
69 is connected at the other end in series with a filament
71 of the other lamp 45 across a winding section X4. Lamp
45 has a filament 73 at the other end which is connected
across winding section X5. A capacitor C4 is connected
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between the upper sides of winding section X4 and the
upper end of winding section X3, being provided for
causing lamp 45 to ionize before lamp 43. In operation,
it will be seen that the new circuitry 55 provides not
S only high voltage across electrodes 37, 39 at high
frequency, but also provides high frequency AC energization
at lower voltage for energization of lamps 43, 45, again
at the high operating frequency of the circuit.
Such high frequency energization of the grids 37,
39 and lamps 43, 45 provides numerous advantages in the
new electronic insect killer.
Typically, as noted, insect electrocution devices
utilizing high voltage must have the high voltage supply
limited to a relatively low maximum current, such as 10
mA, for safety purposes and specifically to ensure against
electrocution of persons or animals. It will be understood,
for example, that the human body represents a discrete
resistance (which may be assumed to be 1.5 kilo-ohm),
shunted by an extrinsic capacitance which may be assumed
to be 0.15 microfarad. Therefore, the effective impedance
of the human body is complex, being frequency dependent.
But because of the capacitive effect of the human
body, thorasic current distribution at high frequencies is
far more favorable. Accordingly, a much higher current
may be utilized at the high frequency typically of the new
circuit 55, in contrast with the usual line voltage
frequency of 60 Bertz upon which certification standards
have been based. As a consequence, the new circuit allows
a load current of 20 mA to flow from the high voltage
winding Xl without compromising human safety. Accordingly,
the new circuit makes available much more electrical power
for carbonizing insects, thereby avoiding clogging, over-
loading, etc., than prior art electrocution devices.
649
Further, the intrinsic efficiency of the new circuitry
may approach about 90 percent under full load conditions,
in contrast with prior art electruction device~ which may
be able to obtain efficiencies of only about 60 - 70
percent.
It is also manifest that no ballast transformers or
other ballasting devices are needed for fluorescent lamps
43, 45, the high reactance secondary winds interconnected
with such lamps obviating such ballasting. Additionally,
fluorescent lamps of the present character, each of which
may have a 40 watt rating, operate much more efficiently
at higher frequencies, being typically 20 - 30 percent
more efficient at operating frequencies of 4 kHz and
decidedly more efficient at the nominal preferred operating
frequency of the new circuit, namely 20 kHz.
Further advantages of the circuit result from the
self-regulating character of the new inverter circuit
wherein feedback voltages are developed by primary winding
sections PR3, PR4 for driving tran~lstors Ql, Q2 alter-
nately into conduction, as well as resulting from the
intrinsic precision of voltages developed across the secondary
winding. Therefore, high voltage regulating devices, such
as expensive varistors typically used in prior art devices,
are dispensed with.
Moreover, the new circuit is inherently self-
protected against the possibility of a short circuit. For
example, if a conductive object should bridge electrodes
37, 39, the same will merely cause the magnetic field in
core 61 of transformer Tl to collapse, preventing base
drive from being developed by the feedback windings PR3,
PR4. Therefore, both of the transistors Ql, Q2 cease
alternate conduction upon any short circuitint of the
secondary winding.
Referring to FIGURE 6, there is illustrated alter-
native circuitry of the invention which operates to preferably
provide high DC voltage for electrodes 3?, 39, although
it may instead be utilized to provide high AC voltage.
~ lLt;9649
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The circuitry of FIGURE 6 i9 adapted to operate at some-
what higher frequencies than the circuitry of FIGURE 5.
AC voltage i8 applied, typically at 120 VRMS, by a
plug PL2 to a line filter LFl and through a fuse Fl to a
full-wave rectifier including diodes D10 - D13 for pro-
viding two DC voltages. Diodes D10 - D13 and filter
capacitor C6 provide a DC voltage used in conjunction
with a field effect transistor (FET) Q3 for providing a
high frequency alternating voltage to the primary winding
PRl of a transformer T2. A second DC voltage i8 developed
by capacitors C7 and C8, as well as a diode D14 and
zener diode ~15. This voltage is preferably 12 volts
for being supplied to an 06cillator circuit Zl. The
latter is a commercially available integrated circuit
timing device, such as type 555. Such low voltage also
provides drive for switching element Q3. Control voltage
for overload circuitry is also driven from this low
voltage ~ource.
Line filter LFl i8 preferred for preventing AC
noise from being coupled into the circuitry as well as
for preventing high freguency noise generated by the
circuitry from being tran~ormed onto the AC power line
to which plug PL2 i8 connected, thereby preventing the
circuitry from causing excessive EMI. Of course, different
input voltages can be utilized, such as 208 VRMS, 240
VRMS, or DC voltages may be provided directly to the
circuitry, such as at 12, 24, and 48 volts, in which
case the power supply components are omitted.
The integrated circuit timer Zl provides a high fre-
quency pulse train to control the gate terminal of FET
Q3, which is of the N-channel type. Circuit timer Zl
may provide a pulse repetition rate of from about 2 to 100
kHz, it being preferred to utilize relatively high fre-
quency such as 20 - 40 kHz or more.
.
-13-
Interconnected with timer circuit Zl are resistors
RS, R6, diodes D17, D18 and capacitor C10 which determine
the circuit's output frequency or pulse repetition rate,
and duty cycle. Capacitor Cll provides a bypass filtering
S functi~n to prevent noise on the 12 VDC supply potential
from causing erratic operation of circuit Zl.
Overload protection for the circuitry is provided
by a NPN transistor Q4, resistors R8, R9 and R10, and
a capacitor C13. As current flows through R10, a voltage
is developed, which is selectively applied through a
variable resistance or potentiometer Rll for setting a
threshold voltage for conduction of transistor Q4.
Capacitor C13 provides a low pass filter function for
operation of Q4. If the predetermined threshold voltage
thus established for the base of ~4 is exceeded, Q4
becomes conductive for clamping pin 4 of timer circuit Zl
to ground, thus providing a reset condition for the circuit
to prevent oscillation. The output of the timer circuit,
is, accordingly, held at ground potential until the reset
voltage returns to ~ 12 VDC a~ permitted when transistor
Q4 once more becomes non-conductive. In order to protect
FET Q3 from excessive drain-to-source current and voltage
stresses, load line shaping is provided by diode Dl9,
resistor R12, and capacitor C14. Hence, safe operating
limits for FET Q3 are realized. This technique is also
applied to the circuitry of FIGURE 7.
In view of the foregoing, it will be apparent that
timer circuit Zl drives the gate of FET Q3 at the pre-
determined pulse repetition rate to apply DC pulses across
primary winding PRl. A secondary winding Xl, being fabricated
with a universal winding technique, thus developes high
voltage for being supplied across electrocution grid
electrodes 37, 39. In order to prevent excessive AC current
due to the low impedance of electrocution grids 37, 39 as a
result of the high operating frequency, diode D20 and
filtering capacitor C15 provide instead a high DC voltage
across electrocution grids 37, 39. This voltage may be
from typically 4500 VDC to 15,000 VDC and is determined by
the free air break-over voltage intrinsically characteristic
of the physical spacing and configuration of electrodes 37, 39.
4~
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. As will be apparent, secondary windings X2, X3,
X4, and X5 of transformer T2 are interconnected with
fluorescent lamps 43, 45 precisely as in FIGURE 5.
Additionally, a capacitor C16 is connected across
S lamp 43, for starting. Capacitor C4 provides, as in
FIGURE 5, reactance for the AC voltage applied across
the lamps. But, such voltage is, of course, small compared
with that applied across grid electrodes 37, 39.
In lieu of FET Q3, the circuitry of ~IGURE 7 may
be utilized. It is connected, as indicated at A, B,
C, and D in the circuitry of FIGURE 6 and constitutes
a bipolar replacement for the FET. Referring to FIGURE
7, such circuitry includes a pair of NPN transistors
Q5, Q6, resistors R14 - R17, and diodes D21 - D24.
Accordingly, it will be seen that several objects
of the invention are attained and various other advantages
also result.
Although the foregoing includes a description of the
best mode contemplated for carrying out the invention,
various modifications are contemplated.
As various mod~f~cations could be made in the
constructions herein described and illustrated without
departing from the scope of the invention, it i9 intended
that all matter contained in the foregoing description or
shown in the accompanying drawings shall be interpreted as
illustrative rather than limiting.
