AU2003100627A4 - An Improved Electric Fence Energiser - Google Patents

Description

AUSTRALIA

Patents Act 1990 INNOVATION PATENT SPECIFICATION Name of Applicant: Address for Service: Invention Title: Pakton Developments Pty Ltd CULLEN CO Patent Trade Mark Attorneys, 239 George Street Brisbane QId 4000 Australia An Improved Electric Fence Energiser This invention is described in the following statement:

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Field of the Invention The present invention relates generally to electric fences and, in particular, to energisers for electric fences.

Although the invention will be described with particular reference to energisers that are used to energise electric fences in strip grazing or temporary fencing applications, it will be appreciated that the invention may be employed with energisers that are used to energise electric fences in other applications.

Brief Discussion of the Prior Art Electric fences are widely used to restrict the movement of both farm and feral animals. Such fences normally include a plurality of electrically insulated posts between which one or more uninsulated wire conductors are strung. The conductors are coupled to an energiser that periodically outputs a high voltage pulse to energise the conductors so that an animal will receive a small electric shock if it wanders too close to the fence and contacts the energised conductors.

The most popular energisers are small battery powered units that are often used to energise electric fences in strip grazing or temporary fencing applications. Most modern energisers of this type include a discharge capacitor, a capacitor charging circuit for charging the capacitor to a high potential several hundred volts), and a capacitor discharging circuit for discharging the capacitor to produce a very high potential output pulse (e.g.

several thousand volts) that is used to energise the fence conductors.

The capacitor charging circuit is typically a voltage converter circuit that converts the relatively low terminal voltage of the battery to the high voltage required to charge the capacitor. The voltage converter is usually an isolated flyback circuit that includes a step-up transformer that isolates the capacitor discharging circuit from the battery.

The capacitor discharging circuit typically includes a semiconductor switch and a step-up transformer that are both coupled to the capacitor such that the capacitor is able to be discharged through the transformer's primary winding by closing the switch to thereby produce a high voltage pulse across the transformer's secondary winding that can be used to energise the fence conductors.

A schematic circuit diagram of a typical electric fence energiser is illustrated in Fig. 1. The prior art energiser 10 includes a discharge capacitor C1, a capacitor charging circuit 11, and a capacitor discharging circuit 12.

The capacitor charging circuit 11 is an isolated flyback circuit that includes an input terminal 13, a step-up transformer T1, an NPN transistor Q1, an oscillator, and a diode D1. The input terminal 13 includes contacts 14 and 15 that are respectively connected to the positive and grounded negative terminals of a DC power source (not shown) such as a battery. The primary winding of transformer T1 is connected to contact 13 and to the collector of transistor Q1, while the emitter and base of transistor Q1 are respectively connected to ground and the output of the oscillator. The secondary winding of transformer T1 is connected to the anode of diode D1 and to ground. The cathode of diode D1 is connected to the anode of capacitor C1 whose cathode is connected to ground.

The oscillator modulates current that passes through the primary winding of transformer T1 by repeatedly switching the transistor Q1 on and off at a sufficiently high frequency so that an AC voltage appears across the secondary winding of transformer T1. The voltage that appears across the secondary winding has an amplitude that is much greater than the amplitude of the modulated input voltage across the primary winding owing to the stepup transformer action of the transformer TI. The voltage across the secondary winding of transformer T1 is half-wave rectified by the diode D1 and is used to charge the capacitor Cl.

The capacitor discharging circuit 12 includes a step-up transformer T2, a silicon-controlled rectifier (SCR) Q2, a timing/triggering circuit, and an output terminal 16. The primary winding of step-up transformer T2 is connected to the anode of capacitor Cl and to the anode of SCR Q2. The cathode and gate of the SCR Q2 are respectively connected to ground and the output of the timing circuit. The secondary winding of transformer T2 is connected to contacts 17 and 18 of the output terminal 16.

The capacitor discharging circuit 12 periodically discharges capacitor C1 through the primary winding of transformer T2 by periodically triggering SCR Q2. In particular, the timing circuit periodically outputs a voltage of short duration to the gate of SCR Q2 to switch the SCR Q2 on so that charge which has been accumulated by capacitor Cl is discharged through the primary winding of transformer T2 and through the SCR Q2. As capacitor C1 is discharged, a voltage pulse appears across the secondary winding of transformer T2 and between the contacts 17 and 18 of the output terminal 16. The amplitude of the voltage pulse is much greater than the voltage across the charged capacitor C1 owing to the step-up transformer action of transformer T2. Once the current flowing through the primary winding of transformer T2 decreases below the holding current of the SCR Q2, which is the minimum current required to maintain the SCR Q2 switched on, the SCR Q2 switches off with the result that the current path from capacitor Cl to ground through the primary winding of the transformer T2 is no longer available to discharge capacitor C1. After SCR Q2 switches off the charge/discharge cycle is repeated.

Although electric fence energisers of the type that employ an isolated flyback circuit to charge a discharge capacitor perform quite satisfactorily, the isolated flyback circuit adds significantly to both the complexity and cost of manufacture of these types of energisers.

It is an object of the present invention to provide an electric fence energiser that overcomes, or at least ameliorates, one or more of the deficiencies of the prior art electric fence energisers mentioned above, or that provides the consumer with a useful or commercial choice.

Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, various embodiments of the present invention are disclosed.

Summary of the Invention According to an aspect of the present invention there is provided an electric fence energiser for energising the conductors of an electric fence, the energiser including a discharge capacitor, a capacitor charging circuit for charging the capacitor, and a capacitor discharging circuit for discharging the capacitor to energise the fence conductors, the energiser being characterised in that the capacitor charging circuit is a non-isolated flyback circuit.

The use of a non-isolated flyback circuit to charge the capacitor allows the energiser according to the present invention to be substantially less complex and expensive compared to prior art energisers that use an isolated flyback circuit. One of the main reasons for this is that the non-isolated flyback circuit, unlike the isolated flyback circuit, does not require a large and expensive step-up transformer.

In a preferred form, the capacitor discharging circuit includes a silicon-controlled rectifier (SCR) that is coupled to the capacitor such that the capacitor is dischargeable by triggering the SCR. The capacitor charging circuit may be coupled to the capacitor by an impedance such that the impedance limits the current that passes through the SCR and that is drawn directly from the charging circuit to less than the holding current of the rectifier. Alternatively, the energiser may include a switch for preventing the capacitor charging circuit from charging the capacitor while the capacitor is being discharged. The inclusion of the impedance or the switch prevents the SCR from conducting after the capacitor has been discharged.

Brief Description of the Drawings In order that the invention may be more fully understood and put into practice, various preferred embodiments thereof will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic circuit diagram of a prior art electric fence energiser; Fig. 2 is a schematic circuit diagram of an electric fence energiser according to a first embodiment of the present invention; and Fig. 3 is a schematic circuit diagram of an electric fence energiser according to a second embodiment of the present invention.

Detailed Description of the Preferred Embodiments Referring to Fig. 2, an electric fence energiser 20 according to a first embodiment of the present invention includes a discharge capacitor Cl, a capacitor charging circuit 11, and a capacitor discharging circuit 12.

The capacitor charging circuit 11 is a non-isolated flyback circuit that includes an input terminal 13, an inductor L1, an NPN transistor Q1, an oscillator, and a diode D1. The input terminal includes contacts 14 and that are respectively coupled to the positive and grounded negative terminals of a DC power source (not shown) such as a battery. The inductor L1 couples contact 14 to the collector of transistor Q1, while the emitter and base of transistor Q1 are respectively connected to ground and the output of the oscillator. The collector of transistor Q1 is also connected to the anode of diode DI.

The capacitor charging circuit 11 is coupled to the capacitor Cl by an impedance 21. The impedance 21 includes a resistor R1 and a capacitor C2. The resistor R1 is connected to the cathode of diode D1 and to the anode of capacitor C1 whose cathode is connected to ground, while the capacitor C2 is connected to the cathode of diode D1 and to ground.

The oscillator modulates current that passes through the inductor L1 by repeatedly switching transistor Q1 on and off. When transistor 01 is switched on current flows through the transistor Q1 and the inductor L1 which stores energy in its magnetic field. When transistor Q1 is switched off the voltage across inductor L1 changes polarity and briefly spikes so that a current, called a flyback current, is forced through diode D1 and charges capacitors Cl, C2 so that the voltage that appears across the capacitors C1, C2 is significantly greater than the voltage of the power supply.

The capacitor discharging circuit 12 is identical to the previously described capacitor discharging circuit of the prior art energiser The presence of the impedance 21 ensures that any current that passes through the SCR 02 and that is drawn directly from the capacitor charging circuit 11 is limited to less than the holding current of the SCR Q2 so that the SCR Q2 does not remain switched on when the capacitor C1 has been discharged. The value of the resistor R1 is chosen to cause only minimal power losses at the low currents in the high voltage circuit.

Once the capacitor C1 has been discharged by the capacitor discharging circuit 12 the SCR Q2 switches off and the charge/discharge cycle is repeated.

Referring to Fig. 3, an electric fence energiser 30 according to a second embodiment of the present invention includes discharge capacitors C11, a capacitor charging circuit 11, and a capacitor discharging circuit 12.

The components of the energiser 30 that are identified in Fig. 3 with references that include the letter as a suffix are surface mount components that may be used instead of the components that are identified with references that are identical to those of the surface mount components except for the absence of the aforementioned suffix. For example, a diode that is identified in Fig. 3 with the reference DIA is a surface mount diode that may be used instead of a diode that is identified with the reference DI.

The capacitor charging circuit 11 is a non-isolated flyback circuit that includes an input terminal 13, diodes D1, 02, 08, D9 and D12, zener diodes Dl1 and 014, transistors Q1 and Q4, timer IC1, switch SWI, inductor L1, capacitors C1, C3, C8, C13, C15 and C17, and resistors R1, R3, R5, R7, R9, R13, R14, R15, R16, R17, R18, R19, R24 and R25 that are interconnected as shown in Fig. 3.

The capacitor charging circuit 11 is coupled to the discharge capacitors C10 and C11 by an impedance 21. The impedance 21 includes a resistor R2 and a capacitor C9.

The capacitor discharging circuit 12 includes an output terminal 16, diodes 08 and D9, light emitting diode 015, transistor Q5, timer IC2, SCR 03, step-up transformer Txl, capacitors C2, C4, C5, C6 and C14, and resistors R4, R6, R8, R10, R11, R12, R20, R21, R22, R23 and R26 that are interconnected as shown in Fig. 3.

Timers IC and IC2 are both LMC555 timers that are manufactured by National Semiconductor Corporation. A detailed description of the LMC555 timer can be found in the manufacturers datasheets for the device. Both IC1 and IC2 are configured as free running oscillators.

Timer IC1 functions as the oscillator for the capacitor charging circuit 11 and outputs a square wave having a duty cycle of roughly 50% on pin 3. The frequency of the square wave is 10kHz and is set by resistor R3 and capacitor C13. Pin 3 of timer IC1 is coupled to the base of transistor Q1 so that transistor Q1 is switched on when the output on pin 3 is high and is switched off when the output on pin 3 is low. When transistor Q1 is switched on current from the power supply flows through transistor Q1 and inductor L1 which stores energy in its magnetic field. When transistor Q1 is switched off the voltage across the inductor L1 changes polarity and briefly spikes so that a flyback current is forced through diode D2 and charges capacitors C10 and C11 to approximately 300V. Once the capacitors C10 and C11 have been charged to this voltage the zener diode D14 starts to conduct which switches on transistor Q4 so that timer ICI is shutdown to save power. The presence of resistor R19 which is connected to pins 3 and 4 of timer IC1 provides some hysteresis to the reset action of timer IC1 so that the timer switches off cleanly when the capacitors C10 and C11 have been charged.

Timer IC2 functions as the timing circuit for the capacitor discharging circuit 12 and outputs a square wave on pin 3. The square wave has a frequency of approximately 0.7Hz which is the frequency at which the SCR Q3 is triggered. The off time of the square wave is a function of the values of resistor R20 and capacitor C14, while the on time is a function of the values of resistor R11 and capacitor C14. Pin 3 of timer IC2 is coupled to light emitting diode D15 and the base of transistors Q4 and Q5 so that when the output on pin 3 is high diode D15 emits light and transistor Q4 is held on ensuring that timer IC1 is shutdown. Also, transistor Q5 is turned on briefly while capacitor C5 charges which in turn causes SCR Q3 to switch on. When SCR Q3 switches on capacitors C10 and C11 are discharged through the primary winding of transformer Txl so that a high voltage pulse appears across the secondary winding of transformer Txl which has a turns ratio of 1:18. SCR Q3 switches off once the current passing therethrough falls below the holding current of the SCR. After the SCR Q3 switches off the charge/discharge cycle is repeated.

The impedance 21 limits the current that passes through the SCR Q3 which is drawn directly from the capacitor charging circuit 11 to less than the holding current of the SCR so that the SCR Q3 does not remain switched on after the capacitors C10 and C11 have been discharged.

Diodes D1 and D12 offer reverse voltage protection and prevent a 12V battery power supply from charging an internal 6V battery.

Resistor R1 acts as a fuse to prevent a current surge from damaging the energiser Zener diode DlI1 prevents overvoltage from occurring which would damage the timers IC1 and IC2.

Capacitor C8 smooths the power supply voltage, while capacitors Cl and C4 decouple the timers IC1 and 1C2 from the power supply.

Switch SW1 is used to switch the energiser 30 on and off.

The foregoing describes only two embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. For example, instead of including an impedance to limit the current that passes through the SCR, the energiser may include a switch for preventing the capacitor charging circuit from charging the discharge capacitor while the capacitor is being discharged.

Claims (4)

1. An electric fence energiser for energising the conductors of an electric fence, the energiser including a discharge capacitor, a capacitor charging circuit for charging the capacitor, and a capacitor discharging circuit for discharging the capacitor to energise the fence conductors, the energiser being characterised in that the capacitor charging circuit is a non-isolated flyback circuit.

2. The energiser of claim 1, wherein the capacitor discharging circuit includes a silicon-controlled rectifier that is coupled to the capacitor such that the capacitor is dischargeable by triggering the rectifier.

3. The energiser of claim 2, wherein the energiser also includes an impedance that couples the capacitor charging circuit to the capacitor such that the impedance limits the current that passes through the rectifier and that is drawn directly from the charging circuit to less than the holding current of the rectifier.

4. The energiser of claim 2, wherein the energiser also includes a switch for preventing the capacitor charging circuit from charging the capacitor while the capacitor is being discharged. An electric fence energiser substantially as herein described with reference to Fig. 2 or Fig. 3 of the drawings. DATED this 1 st day of August 2003 Pakton Developments Pty Ltd By their Patent Attorneys CULLEN CO.