GB2155716A

GB2155716A - A high voltage pulse generator

Info

Publication number: GB2155716A
Application number: GB08504390A
Authority: GB
Inventors: David Reynolds Gray; David William Govan
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-02-22
Filing date: 1985-02-20
Publication date: 1985-09-25
Also published as: IE55329B1; GB2155716B; GB8504390D0; IE840413L

Abstract

A high voltage pulse generator is provided for use with an electric fence, which overcomes the problem of generators known heretofore, whereby the energy which can be delivered onto an electric fence falls off as the resistance on the line increases. The generator comprises a transformer (2) having a secondary coil (3) and primary coil (4), the charge is delivered from the secondary coil (3). A pair of primary capacitors (10 and 11) are connected across the primary coil (4) and with the coil (4) form an oscillating circuit (12) which causes the capacitors (10 and 11) to continuously discharge and charge, thereby increasing the energy which may be delivered onto the fence line. The circuit (12) is opened and closed by a triac (14) which is controlled by timing circuits comprising a resistor (23) and a capacitor (24), and a resistor (28). An AC supply is delivered to the capacitors (10 and 11) through a rectifying circuit with diodes (18 and 19). <IMAGE>

Description

SPECIFICATION A high voltage pulse generator The present invention relates to a high voltage pulse generator, and in particular, to a high voltage pulse generator for use with an electric fence.

Such fences are generally used on farms, game reservations and the like, to confine animals to a particular area. A charge is delivered from the generator along the line of the fence, and an animal coming in contact with it receives a shock not sufficient to injure the animal, but nonetheless sufficient to cause discomfort, thus keeping the animal away from the fence. It is important that the energy transferred along the line from the generator is at all times sufficient to cause discomfort to the animal. Unfortunately, with known generators, this is not always possible.The main problem that arises with known generators is that the energy transferred onto the line is inversely proportional to the resistance on the line, and thus, where a high resistance is encountered, the energy delivered is relatively low, and in many cases not sufficient to cause discomfort to an animal, and the animal merely forces its way across the fence. There is therefore a need for a high voltage pulse generator which overcomes the problems of generators known heretofore.

The present invention is directed towards providing such a high voltage pulse generator.

According to the invention, there is provided a high voltage pulse generator comprising a transformer having a secondary winding across which the high voltage pulse is provided, and a primary winding, at least one primary capacitor connected across the primary winding of the transformer to store a charge for discharge through the primary winding, the primary capacitor and primary winding forming an oscillating circuit, and a switch means to close the circuit between the capacitor and the primary winding for discharging of the capacitor.

In one embodiment of the invention the primary capacitor is a non-polarised capacitor.

Preferably, a first timing circuit is provided to activate the switch means at predetermined intervals.

Advantageously, a second timing circuit is provided to hold the switch means closed for a predetermined period, to allow the primary capacitor to discharge through the primary winding.

In one embodiment of the invention, a pair of primary capacitors in series are provided across the primary winding of the transformer.

Preferably, the primary capacitors are connected to form part of a rectifying circuit to receive and sum the positive and negative components of an AC supply.

In another embodiment of the invention, the switch means is provided by a triac in the circuit of the primary capacitor and the primary coil of the transformer between the primary capacitor and the primary coil, and a diac to trigger the triac is provided.

In another embodiment of the invention, the first timing circuit is powered by the or each primary capacitor.

In another embodiment of the invention, the first timing circuit comprises a resistor and a timing capacitor in series connected across the or each primary capacitor.

In another embodiment of the invention, the second timing circuit comprises the timing capacitor of the first timing circuit, and a resistor between the timing capacitor and the triac.

The invention will be more clearly understood from the following description of some preferred embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which: Fig. lisa circuit diagram of a high voltage pulse generator according to the invention; Fig. 2 is a graph of the output from the high voltage pulse generator of Fig. 1; Fig. 3 is a circuit diagram of a high voltage pulse generator according to another embodiment of the invention; and Fig. 4 is a graph of the voltage across the primary capacitor of the generator of Fig. 3.

Referring to the drawings, and initially to Fig. 1, there is provided a high voltage pulse generator indicated generally by the reference numeral 1. The generator comprises a transformer 2 having a secondary coil 3 and a primary coil 4 with 700 and 70 turns respectively. The high voltage pulses are delivered onto contacts 7 and 8 tapped off the secondary coil 3, and an earth contact 9 on the other end of the secondary coil 3, is provided. In use, the electric fence is connected to the contacts 7 of 8, depending on the voltage required. In this case, the contact 7 delivers 5,500 V and the contact 8 delivers 2,500 V.

A pair of primary capacitors 10 and 11 are connected in series with the primary coil 4 of the transformer 2, for building up and discharging a charge through the primary coil 4. In this particular case, the capacitors are non-polarised capacitors of 30 microfarads each and form with the primary coil 4 an oscillating circuit 12 thereby permitting the charge to oscillate in the circuit formed by the capacitors 10 and 11 and the primary coil 4. A switch means, in this case a triac 14, is provided in the oscillating circuit 12, to close the circuit. This will be described below.

An AC supply is delivered through connectors 5 and 6 onto the primary capacitors 10 and 11 at points 15,16 and 17, through a rectifying circuit which comprises a pair of diodes 18 and 19. Thus, the AC supply is rectified and the positive component is put onto one primary capacitor, while the negative component is put onto the second primary capacitor, and the two components are thus summed, thereby giving the maximum peak voltage across the pair of capacitors 10 and 11. Load resistors 20 and 21 are provided in the rectifying circuit. The resistors 20 and 21 are each of 1,000 ohms resistance. A thermistor 22 is provided in the AC supply circuit to protect the generator against internal shorts and overheating.

Dealing now with the triac 14, the triac 14 is triggered at intervals of approximately one second by a first timing circuit, and held closed for a period of 10 milliseconds, by a second timing circuit. The first timing circuit comprises a resistor 23 and a timing capacitor 24 connected in series across the primary capacitors 10 and 11. In this case, the resistor 23 is a 200 kilo ohm resistor, and the timing capacitor 24 is a 100 microfarad capacitor. This timing circuit triggers a diac 26 which in turn triggers the triac 14. A second timing circuit is formed by the timing capacitor 24, and a resistor 28, which is connected between the diac 26 and the triac 14. In this case the resistor 28 is a 100 ohm resistor.

A discharge resistor 29 of 10,000 ohms is connected across the triac. Because of the fact that the resistor 23 and the timing capacitor 24 are of 200 kilo ohms and 100 microfarads respectively, they trigger the diac 26 at intervals of approximately one second.

Needless to say, if it were desired to alter the triggering interval, this would merely require altering the values of the resistor and timing capacitor. Similarly, by virtue of the fact that the resistor 28 is sized as 100 ohms, this also ensures that the triac will be held closed for 10 milliseconds.

Again, if it were desired to alter this period, this could be done by altering the value of the resistor 28.

In use, the generator is connected to an AC source by the connectors 5 and 6. The electric fence is connected to either of the desired connectors 7 or 8.

The earth contact 9 is connected to an earth spike (not shown) driven approximately three feet into the ground. The primary capacitors 10 and 11 are charged by the AC mains, with the triac 14 open. The first timing circuit provided by the resistor 23 and timing capacitor 24 time one second intervals and after the first second the triac is triggered. The second timing circuit provided by the timing capacitor 24 and the resistor 28, holds in the triacfor the period of 10 milliseconds. During this period, the circuit formed by the primary capacitors 10 and 11, and the primary winding 4 of the transformer, acts as an oscillating circuit, thereby continuously discharging and charging the capacitors 10 and 11.

This operation continues, thus causing a high voltage charge to be delivered onto the secondary winding of the secondary winding 3 of the transformer 2, and in turn onto the electric fence for 10 milliseconds every second. Fig. 2 illustrates a graph showing the voltage wave form on the secondary coil.

By virtue of the fact that the capacitors 10 and 11 are non-polarised capacitors, they form with the primary coil 4 an oscillating circuit which therefore enables the discharge from the generator to last considerably longer than in high voltage pulse generators known heretofore, and because the charge oscillates around the circuit, the energy delivered onto the fence is much less dependent on the line load on the fence than generators known heretofore. Needless to say, if the triac were held in for a longer period, a further charge would be delivered by the secondary coil 3.

Referring now to Fig. 3, there is illustrated a circuit diagram of a high voltage pulse generator 40, according to another embodiment of the invention.

In this case, the generator is suitable for powering by a battery 41 instead of AC mains. In this case, the circuit comprises a transformer 42 having a secondary coil 43, and a primary coil 46. The secondary coil is connected to an electric fence and to earth in similar fashion as the transformer of the generator of Fig. 1. A primary capacitor 44 is connected across the primary coil 46 of the transformer 42, and the primary capacitor 44 is fed through a voltage converter 45 from the battery 41.

A switch means provided by an AC switch 47 is connected between the primary capacitor 44 and the primary coil 46 to close the circuit formed by the primary capacitor 44 and the primary coil 46, the AC switch 47 also comprises timing means to close the switch at intervals of approximately one senond, and to hold the circuit closed for periods of 10 milliseconds. The switch 47 is a triac substantially similar to the triac used in the generator of Fig. 1.

The timing means are provided by a pair of timing circuits, also similar to those of the generator of Fig.

1. Although, not illustrated, a voltage sensor is provided on the voltage converter to control the voltage and to avoid unnecessary draw off of energy from the battery.

The operation of th is generator 40 is substantially similar to that described, and will be readily apparent to those skilled in the art.

It is envisaged that in certain cases the triac and timing circuit may be arranged to open the oscillating circuit after one full cycle. This has the considerable advantage of reducing the energy drawn off from the battery. After a one cycle discharge, the primary capacitor only has to be restored to its original charge. Thus, if the load impedence across the secondary coil is iow, the primary capacitor will only have to be topped up by a small amount. This leads, needless to say, to considerable saving on the battery. Fig. 4 illustrates a graph of the voltage across the primary capacitor after a one cycle discharge. In this case, the secondary load is greater than 7,000 ohms, and as can be seen, the voltage restoration is only 200 volts, in other words, from 400 volts to 600 volts.In the case of a conventional pulse generator, after discharge the capacitor would have to be charged up from 0 to 600 volts.

It is envisaged that any suitable timing and switch means could be used to achieve a one cycle discharge, for example, it is envisaged that the timing circuit could be replaced by an astable multivibration switch.

It is envisaged that while in the case of both generators, specific types of switch means have been described, any other suitable switch means could be used, for example, in certain cases, a transistor, or indeed any other suitable switch means could be used. Furthermore, it will be appreciated that other timing means could be used besides the two RC circuits. In fact, any other suitable AC switching or triggering means, or any other suitable means could be used. Additionally, it will be appreciated that in the generator of Fig. 1, it is not necessary to provide two primary capacitors, all that is needed is one primary capacitor.

Although, needless to say, by providing two capacitors and summing the two components of the AC voltage the combined voltage across the capacitors is effectively doubled, thereby enabling the primary coil of the transformer to have half the number of turns. This, it will be appreciated, leads to considerable saving, in that the transformer forms a substantial part of any such high voltage pulse generator, and any reduction in the number of turns of the primary secondary coil, leads to substantial savings in the cost of the transformer.

It will also be appreciated that while a thermistor for protection has been described, that a thermistor could, if desired, be dispensed with and/or other suitable protection means if desired could be provided.

It will also be appreciated that while the various capacitors and resistors have been described as being of particular values, it will be appreciated that any other suitable values may be chosen.

Additionally, numbers of turns in the primary and secondary coils of the transformer could also be varied as desired.

Claims

1. A high voltage pulse generator comprising a transformer having a secondary winding across which the high voltage pulse is provided, and a primary winding, at least one primary capacitor connected across the primary winding of the transformer to store a charge for discharge through the primary winding, the primary capacitor and primary winding forming an oscillating circuit, and a switch means to close the circuit between the capacitor and the primary winding for discharging of the capacitor.

2. A high voltage pulse generator as claimed in claim 1, in which the primary capacitor is a non polarised capacitor.

3. A high voltage pulse generator as claimed in claim 1 or 2, in which a first timing circuit is provided to close the switch means at predetermined intervals.

4. A high voltage pulse generator as claimed in any of claims 1 to 3, in which a second timing circuit is provided to hold the switch means closed for a predetermined period, to allow the primary capacitor to discharge through the primary winding.

5. A high voltage pulse generator as claimed in any preceding claim, in which a pair of primary capacitors in series are provided across the primary winding of the transformer.

6. A high voltage pulse generator as claimed in claim 5, in which the primary capacitors are connected to form part of a rectifying circuit to receive and sum the positive and negative components of an AC supply.

7. A high voltage pulse generator as claimed in any preceding claim, in which the switch means is provided by a triac in the circuit of the primary capacitor and the primary coil of the transformer between the primary capacitor and the primary coil.

8. A high voltage pulse generator as claimed in claim 7, in which a diac is provided to trigger the triac.

9. A high voltage pulse generator as claimed in any of claims 3 to 8, in which the first timing circuit is powered by the or each primary capacitor.

10. A high voltage pulse generator as claimed in claim 9, in which the first timing circuit comprises a resistor and a timing capacitor in series connected across the or each primary capacitor.

11. A high voltage pulse generator as claimed in claim 10, in which the triac is connected to the timing circuit between the resistor and the timing capacitor through the diac.

12. A high voltage pulse generator as claimed in claim 10 or 11, in which the resistor and the timing capacitor are sized so that the timing circuit triggers the diac once per second.

13. A high voltage pulse generator as claimed in any of claims 10 to 12, in which the resistor is in the range 50 kilo ohms to 900 kilo ohms and the timing capacitor is in the range 20 microfarads to 200 microfarads.

14. A high voltage pulse generator as claimed in claim 13, in which the resistor is 200 kilo ohms and the timing capacitor is 100 microfarads.

15. A high voltage pulse generator as claimed in any of claims 4to 14, in which the second timing circuit comprises the timing capacitor of the first timing circuit, and a resistor between the timing capacitor and the triac.

16. A high voltage pulse generator as claimed in claim 15, in which the resistor is connected between the diac and the triac.

17. A high voltage pulse generator as claimed in claim 15 or 16, in which the resistor is in the range 50 ohms to 500 ohms.

18. A high voltage pulse generator as claimed in claim 17, in which the resistor is 100 ohms.

19. A high voltage pulse generator as claimed in any of claims 15 to 18, in which a second resistor is provided across the triac to discharge the second timing circuit.

20. A high voltage pulse generator as claimed in claim 19, in which the second resistor is in the range 1,000 ohms to 50,000 ohms.

21. A high voltage pulse generator as claimed in claim 20, in which the second resistor is 10,000 ohms.

22. A high voltage pulse generator as claimed in any preceding claim, in which the or each primary capacitor is in the range of 5 microfarads to 100 microfarads.

23. A high voltage pulse generator as claimed in claim 22, in which the or each primary capacitor is 30 microfarads.

24. A high voltage pulse generator as claimed in claim 6, in which the or each primary capacitor is connected through a mains resistor and diode.

25. A high voltage pulse generator as claimed in claim 24, in which the mains resistor is in the range 500 ohms to 5,000 ohms.

26. A high voltage pulse generator as claimed in claim 25, in which the mains resistor is 1,000 ohms.

27. A high voltage pulse generator as claimed in any preceding claim, in which a thermistor is provided on the mains inlet to protect the generator against interval shorts and/or overheating.

28. A high voltage pulse generator as claimed in any preceding claim for use with an electric fence.

29. A high voltage pulse generator substantially as described herein, with reference to and as illustrated in the accompanying drawing.

30. An electric fence incorporating the high voltage pulse generator of any of the preceding claims.