Electricity: electrical systems and devices – Control circuits for electromagnetic devices
Reexamination Certificate
1997-04-23
2001-06-19
Fleming, Fritz (Department: 2836)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
C361S143000, C327S181000, C043S124000
Reexamination Certificate
active
06249417
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to rodent repelling devices and, more particularly, to an improved circuit for generating a substantially constant electromagnetic field for repelling rodents.
Various electrical devices have been proposed to repel rodents such as rats and mice from buildings and other structures. One such device is disclosed in U.S. Pat. No. 4,414,653 in which sound waves are generated at a frequency which is irritating to rats and mice. Another form of such device is shown in U.S. Pat. No. 4,802,057 in which a magnetic field is generated with a pulse frequency of approximately 60 cycles per minute, which frequency is known to repel rodents such as rats and mice. The apparatus illustrated in the '057 patent is relatively complicated and requires a rectifier and voltage regulator for producing low voltage DC electrical power from AC electrical power connected to the device. A low voltage circuit generates a pulsed frequency gating signal which gating signal is then applied to an amplifier and from the amplifier to an optical isolator circuit which separates the low voltage circuit from the high voltage control circuit. The high voltage control circuit includes a switch connected in series between a magnetic coil and the AC power source. The switch is controlled by the gating signal passing through the optical isolator. However, the switch also requires more power than is available from the optical isolator and in that regard AC power is coupled through a current limiting resistor to a gate input of the switch. The gating signal from the optical isolator, is summed with AC power and utilized as a gating signal to the switch. During the time that the pulsed gating signal from the optical isolator is coupled to the switch, the AC power is used to gate the switch into and out of conduction. One of the detriments with this system is that the switch is operated at the AC power frequency, i.e., 60 cycles per second (60 Hz), even though the magnetic field is desirably operated at 60 cycles per minute or at a frequency of 1 Hz. Furthermore, due to the phase shift between the voltage and current caused by the inductance of the coil, the circuit produces a reduced power output since the AC gating signals are applied in synchronism with the applied AC voltage across the coil and such voltage is phase shifted from the actual current through the coil. It is believed that the gating of the switch using the 60 Hz AC power signal out of phase with the current through the coil is the cause of a power variation in the electromagnetic field generated by the device illustrated in the '057 patent.
SUMMARY OF THE INVENTION
The present invention is directed to an electrical circuit for energizing a coil for producing a substantially constant pulsed magnetic field. In an illustrative embodiment, the circuit includes an electromagnetic coil for generating a magnetic field in response to AC power applied to terminals of the coil. A gated triac is connected in series electrical circuit with the coil with the series circuit being connectable to a source of AC electric power. A gating signal is applied to a gate terminal of the triac to gate the triac into continuous conduction for a time duration such that a plurality of cycles of the applied AC power is applied across the coil. Preferably, the gating signals are generated at a frequency of 0.5 Hz with a 50% duty cycle so that gating pulses are applied to the gated triac at a rate of 30 pulses per minute with each pulse having a time duration of one second.
The gating pulses are generated by an integrated clock circuit. The clock circuit is timed by the 60 Hz AC power and produces output pulses at a 0.5 Hz rate that are on for three minutes and then off for three minutes. The power to the clock circuit is supplied through a series resistor and capacitor which act as a constant current source from the AC power. A zener diode regulates the positive half-cycle of the AC power to approximately 5.1 volts while shunting the negative half-cycle to ground. The pulsing DC level at the zener diode produces a conditioned 60 Hz clock signal which is applied to the integrated clock circuit for timing. This clock signal is also directed through a diode to a filter capacitor which establishes a unregulated low voltage DC level with AC ripple for powering the clock circuit. The output pulses from the clock circuit are applied as DC logic control signals to the gated triac. The triac controls the current through the coil and when gated into conduction allows the AC power to be applied across the coil for the full extent of the time duration of the gate pulse. A transient snubber circuit is connected across the triac. Since the coil is energized by both the positive and negative going AC power signals during the time duration of the clock pulse, the magnetic field generated by the coil remains substantially constant.
REFERENCES:
patent: 4097838 (1978-06-01), Fiala
patent: 4163966 (1979-08-01), Mounce
patent: 4178578 (1979-12-01), Hall
patent: 4219884 (1980-08-01), DeSantis
patent: 4802057 (1989-01-01), Patterson et al.
patent: 4870779 (1989-10-01), Johnson et al.
patent: 5208787 (1993-05-01), Shirley
patent: 5473836 (1995-12-01), Liu
Beusse, Esq. James H.
Fleming Fritz
Hodgskin Donald
Holland & Knight LLP
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