AU592155B2 - Electric fence energiser - Google Patents

Description

j L "tL P/00/01 I Form PATENTS ACT 1952 COMPLETE SPECIFICATION (OR IG INAL) FOR OFFICE USE Short Titk*i: mnt. CI: Application Number: Lodged: Complete Specification-Lodged, Accepted: Lapsed: Published: Rel~ated Art: t i9 //8 IThis document contains tI.

amendme~ats made un) >i1 Section 49 and is correct £ca Iprintius, Name of Applicant; TO BE COMPLETED BY APPLICANT GALLAGHER ELECT'RONICS LITED Address of Applicant: Actual Inventor, Kahikatea Drive, Hamilton, New Zealand Jeremy John McKis sack Address for Service: BARKER, BLENKINSRTP ASSOCIATES. P.O. Box 34, Chatswood, 2067 Complete Specification for the invention entitled:' ELEM, OgtC FENCE ENERGISER The following statement Is a full description of this invention, including the best method of performing R~ known to me:-* Note., the description Is to be typed In dloubli spacing, pica type face, In an area not exceeding 250 mm In depth and 160 mm In width, on tough white paper of good qua i~y and It Is to be Inseiled Inside this form.

14599/78-L 1 459/78- ~Printed by C. LTtoMPSoN,. Commonwealth Governnment Prinler, Canberra This invention relates to electric fence energisers.

By the very nature of their operation, energisers are responsible for radio interference and in countries which rely particularly upon radio communication, a reduction in this source of interference would be welcomed. The interference is caused by sharp changes in voltage across the output terminals of the energiser.

This invention provides an electric fence energiser comprising an energy storage capacitor chargeable from a power source, switching means, the action of said switching means being able to cause the discharge of said energy storage capacitor, a transformer having an output being connected to an electric fence to which transformer the discharge from the energy storage capacitor is conducted, the transformer having a resonant circuit associated with the primary or secondary windings thereof, said resonant circuit including a inductor, the inductance of which is sufficient to slow down the rate of discharge of the energy storage capacitor thus reducing radio frequency interference.

According to a further aspect of the present invention there is provided an electric fence energiser as claimed in claim 1 wherein the resonant circuitry consists of an output transformer, the primary windings of which are in parallel with the energy storage capac'or o. and an inductor plus a switching capacitor respectively in series from one terminal of the transformer's primary windings forming a closed loop with the other transformer's primary Swindings.

4 9 Aspects of the present invention will now be described by way of example only with reference SgO to the accompanying drawings in which: Figure 1: is a block diagram of an electric fence energiser according to the present invention, and Figure 2: is a circuit diagram showing in more detail components of the electric fence energiser of Figure 1, and igure 3: is a circuit diagram of a resonant output transformer circuit according to one alternative construction of the present invention, and I t 2 A, Cf Figure 4: is a circuit diagram of a resonant output transformer circuit according to a further alternative construction of the pr'esent invention.

With respect to Figure 1 of the drawings an electric fence energiser according to the present invention comprises a DC-DC converter 1 connected between a DC power source 2 and an energy storage capacitor 3, a discharge path for said capacitor 3 via a resonant output transformer circuit 4 adapted for connection to a fence system and a controllable switch 6 controlled by an independent pulse trigger 7 to provide discharge of said energy storage capacitor approximately once per second, the voltage across said energy storage capacitor 3 having been broelht to a substantially constant peak value immediately prior to discharge by the application of feedback control to said DC-DC converter 1 and the said resonant output transformer circuit 4 providing commutation feedback to said controllable switch 6 such that said energy storage capacitor 3 is discharged to a value dependent upon load conditions of said output circuit and consequently the input energy requirements of said DC-DC converter 1 is also dependent on output circuit load conditions.

The DC power source 2, the DC-DC converter 1 and a feedback circuit 8 and the energy storage capacitor 3 are connected such that the voltage across the capacitor 3 reaches a predetermined value, immediately prior to discharge.

0 Referring now to Figure 2 of the drawings the DC-DC converter 1 operates such that of the S* moment voltage is supplied by battery B 1, a small current flows through resistor R4 into the 0 o% base of the transistor Q3, This causes a larger current to flow in the primary windings of a* the converter transformer Tl. Regenerative action is produced by current flowing in the tickler S- windings through the base of transistor Q3, diode Dl and resistor R5. Diode D2 ensures that transistor Q3 is not damaged by the unwanted negative voltages that are produced by the inverter action by providing an alternative current path. Resistor R5 controls the regenerative action by limiting the current flowing in the base of transistor Q3, The current in the primary windings increases until the transformer Q2 saturates, and at this point the collector current stops increasing thus causing regenerative action to stop. The energy stored in the converter transformer as a magnetic field is then transferred via the secondary windings (a,b) and diode D3 to the energy storage capacitor C4.

Peak voltage across the energy storage capacitor is maintained at a predetermined value by the feedback circuit 8 as zener diode D4 is connected so that negligible current flows through it until the voltage across the energy storage capacitor C4 exceeds the zener voltage. The zener voltage is a property of the zener diode type, the type used being selected for the zener voltage and thus the peak voltage across the capacitor C4 required.

Current flowing through the zener diode flows through resistor R6 and into the base of transistor Q2, causing the transformer to conduct, and thus shunt cuicrent away from the base of the transistor Q3 which then inhibits the regenerative action of the DC-DC converter, which as a result stops further energy transfer to the capacitor C4. This then limits the peak voltage across capacitor C4 to a level predetermined to the zener voltage of zener diode D4.

Capacitor C4 is discharged into the resonant outpnt transformer circuit 4, via controllable switch 6. This switch is controlled by a trigger circuit 7, which is in the form of a typical unijunction transistor relaxation oscillator, having a period fixed by resistor R1 and capacitor C2, of approximately 1 second. The output pulse from this trigger circuit has a pulse width that is less than the commutated turn-off time of the controllable switch 6.

When there is a light load on the output circuit, the discharge of the energy storage capacitor into the resonant output transformer circuit consisting of the output transformer T2, capacitor and inductor L results in a damped sinusoidal voltage to be produced across the primary of transformer T2. As the sinusoidal voltage falls through zero the controllable switch turns a° off, the discharge current from the energy storage capacitor falls to zero, and further discharge is inhibited until the time of the next trigger pulse from the trigger circuit 7. At the moment the discharge of the capacitor C4 is inhibited the voltage across this capacitor will be at some value S° below the predetermined peak value but substantially greater than zero. The DC-DC converter then works to increase the voltage on capacitor C4 back to the predetermined peak value as So described herein.

When there is a heavy load on the output circuit the resonant output circuit 4 is over damped so that the sinusoidal voltage across the controlled switch never reaches a value that will 4 commutate the switch off. As a result the capacitor C4 discharges until the voltage across it is approximately zero. The DC-DC converter then works to charge capacitor C4 until the voltage across the capacitor is increased from approximately zero volts to the predetermined peak voltage. It can be seen from the above that the amount of charge that is removed from the energy storage capacitor, and thus ultimately the amount of energy this charged is dependent upon the load on the output circuit of the electric fence energiser.

9o *l Further, the resonant output transformer has the effect of slowing down the rate of discharge of the energy storage capacitor, a result of which is that the radio interference caused by the voltage produced across the output circuit, is reduced.

Figure 3 of the drawings illustrates a resonant output transformer circuit according to the example described in relation to Figure 2. Figure 4 of the drawings illustrates ao alternative to the Figure 3 circuit where a capacitor C6 is fixed across the output connectin--r of the transformer 2.

The relationship between the current drawing from the DC power source and the loading of the I output circuit can be described as follows: Vd voltage across C4 at the instant that the controllable switch turns off.

Vc peak voltage across energy storage capacitor C4.

VS voltage supplied by battery B 1.

t time between trigger pulses, and thus time between impulses.

C capacitance value of energy storj, e capacitor C4.

Is current drain from battery B 1.

E efficiency of DC-DC converter, a factor less Chan 1.

am 0 From conservation of energy we have: Vsxlsxt 0 .5xCx(Vc-Yd) 2 E Equation (1) (energy input (energy stored) x (energy wastage factor).

Rearranging Equation gives the battery current drain.

004Is .5xCxCVc-Vd) 2 /E (Vsxt) Equation (2) 6 $A For a given circuit most of the above variables are in fact essentially constant. These can then U be lumped together so that Equation. can be rewritten: Is Kx(Vc-Vd) 2 Equation (3) 7 It It is clearly seen from Equation that the battery current is dependent upon Vd. In the case of a heavily loaded output circuit Vd is zero so that (Vc-Vd) and therefor Is, is maximised.

For a lightly loaded output circuit Vd is almost equal to Vc so that (Vc-Vd) and therefor Is is minimised.

Although in the embodiment described herein by way of example, the electric fence energiser is shown to include a DC-DC converter it is to be appreciated that this is not essential to the primary function of the present invention.

a C C0 CCCCC8 s8c cC C C9

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Claims (2)

1. 3. An electric fence energiser as claimed in either claim 1 or 2 wherein the resonant circuit comprises a capacitor in parallel with the transformer primary connections and an inductance forming a series circuit S- 4 43 ,5i fl -8- between one transformer primary connection and said switching means.
2. 4. An electric fence energiser as claimed in either claim 1 or claim 2 wherein the resonant circuit includes a capacitor in parallel with the secondary connections of the transformer. An electric fence energiser as claimed in any one of claims 1 to 4 wherein the power source includes a convertor and the transformer is electrically connected to 10 the convertor via a feed back control circuit, said control circuit controlling input from the power source to o" be dependant upon the load the fence imposes. 'it 6. An electric fence energiser as claimed in claim 5 hereof pIi# wherein the feedback control circuit comptries a Zener diode controlling a transistor, the arrangement being such that the regenerative action of the convertor is inhibited *0 by the feedback control circuit to livmit voltage output from the energy storage capacitor to a level determined by the diode. 4 II I I DATED this 17th day of October 1989 l GALLAGHER ELECTRONICS LIMITED