GB2122821A - High voltage circuit electrical apparatus - Google Patents

Abstract

A high speed chopping circuit 10 is operable to repeatedly discharge a capacitative element C4 in series with a primary coil of at least one step-up transformer T5. When the supply is A.C., a triac 10 activated by a diac 12 or a multi- vibrator is used as the chopping circuit. When the supply is D.C. thyristor/diode circuitry is used. The transformer is preferably of the sectionally-wound ferrite-cored type. <IMAGE>

Description

SPECIFICATION High voltage circuit The invention relates to electronic apparatus for the production of high voltages particularly though not exclusively suitable for research purposes in schools, laboratories and other institutions.

At the present time the most common way of achieving high voltages is usually by the use of an induction coil. Unfortunately present day induction coils make use of a mechanical make and break mechanism, are very noisy and often develop a shorted turn in the secondary coil thus rendering the apparatus useless.

There has long been a demand for apparatus capable of producing high voltages safely and with an earth-free output.

The invention provides electrical apparatus comprising a high speed chopping circuit operable to repeatedly discharge a capacitative element in series with a primary coil of at least one step-up transformer.

Preferably the high speed chopping circuit includes a TRIAC and preferably the TRIAC is activated by a DIAC which supplies a pulsed signal thereto. Alternatively the high speed chopping circuit may include a pair of thyristors in back-to-back arrangement, or if a D.C. supply is used a thyristor and or diode. The transformer is preferably of the sectionally-wound ferrite-cored type, this type having a high resistance secondary so producing a high voltage at low current.

Desirably the frequency of the signal supplied by the DIAC is adjustable by a resistive/capacitive time delay element.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a block diagram showing the various elements of apparatus according to the invention, and Figure 2 is a circuit diagram of the apparatus of Figure 1.

In the block diagram shown in Figure 1 the TRIAC 10 is activated by a DIAC 12 whose frequency is controlled by a time delay element 14. On activation of the TRIAC, an output therefrom discharged a discharge element 1 6 comprising a capacitor and a step-up transformer.

In the circuit shown in Figure 2 a TRIAC 10 provided with an electrical supply 5 of 240 volts RMS at 50 Hz is triggered by a DIAC 12. The DIAC being powered from the supplies, the time delay comprising a resistor R1,variable resistor RV1 and a capacitor C2. The output of the TRIAC is connected to a discharge capacitor C4 in series with primary coil of a step-up transformer TS of the sectionally wound ferrite cored type. The various elements of the circuit are supplied through a choke L1 and capacitor C1 which are present to minimise radio frequency interference during operation of the apparatus.

Operation of the circuit shown in Figure 2 is as follows. Repeated activation of the TRIAC by the DIAC causes the capacitor C4 to repeatedly discharge through the primary coil of the step-up transformer TS which produces a high voltage at output terminals XY of the secondary of the transformer TS. The frequency of the pulses emitted by the DIAC 12 can be adjusted by variable resistor RV1 and this in turn affects the discharge rate of the TRIAC 10.

It will be noted that the output from the step up transformer TS is earth-free and voltages in excess of 100,000 volts at very low current levels can be achieved making the apparatus safe for use in schools.

The capacitor C4 may be replaced by a series parallel arrangement of four similar capacitors to inhibit breaking down.

Various modifications may be made without departing from the scope of the invention For example another pulse producing element such as a multivibrator may be used in place of the DIAC.

The transformer need not be of the sectionally wound ferrite cored type although this is much to be preferred.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to whether or not particular emphasis has been placed thereon.

Claims (filed on 16/6/83) 1. Electrical apparatus comprising a high speed chopping circuit operable to repeatedly discharge a capacitative element in series with a primary coil of at least one step-up transformer.

2. Electrical apparatus as claimed in Claim 1, in which the high speed chopping circuit includes a Triac.

3. Electrical apparatus as claimed in Claim 2, in which the high speed chopping circuit includes a Diac, the Triac being activated by the Diac.

4. Electrical apparatus as claimed in Claim 1, in which the high speed chopping circuit includes a pair of thyristors in back-to-back arrangement.

5. Electrical apparatus as claimed in Claim 4, in which the thyristors are activated by a Diac.

6. Electrical apparatus as claimed in Claim 4, in which the thyristors are actuated by a neon discharge tube.

7. Electrical apparatus as claimed in Claim 1, in which the high speed chopping circuit is operable from a D.C. supply and which includes a thyristor.

8. Electrical apparatus as claimed in Ciaims 1, 4 and 5 in which the high speed chopping circuit is operable from a D.C. supply and includes a diode.

9. Electrical apparatus as claimed in any preceding Claim, in which the transformer is of the sectionally-wound ferrite-cored type having a high resistance secondary to produce a high voltage at low current.

10. Electrical apparatus as claimed in Claim 3,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION High voltage circuit The invention relates to electronic apparatus for the production of high voltages particularly though not exclusively suitable for research purposes in schools, laboratories and other institutions. At the present time the most common way of achieving high voltages is usually by the use of an induction coil. Unfortunately present day induction coils make use of a mechanical make and break mechanism, are very noisy and often develop a shorted turn in the secondary coil thus rendering the apparatus useless. There has long been a demand for apparatus capable of producing high voltages safely and with an earth-free output. The invention provides electrical apparatus comprising a high speed chopping circuit operable to repeatedly discharge a capacitative element in series with a primary coil of at least one step-up transformer. Preferably the high speed chopping circuit includes a TRIAC and preferably the TRIAC is activated by a DIAC which supplies a pulsed signal thereto. Alternatively the high speed chopping circuit may include a pair of thyristors in back-to-back arrangement, or if a D.C. supply is used a thyristor and or diode. The transformer is preferably of the sectionally-wound ferrite-cored type, this type having a high resistance secondary so producing a high voltage at low current. Desirably the frequency of the signal supplied by the DIAC is adjustable by a resistive/capacitive time delay element. An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a block diagram showing the various elements of apparatus according to the invention, and Figure 2 is a circuit diagram of the apparatus of Figure 1. In the block diagram shown in Figure 1 the TRIAC 10 is activated by a DIAC 12 whose frequency is controlled by a time delay element 14. On activation of the TRIAC, an output therefrom discharged a discharge element 1 6 comprising a capacitor and a step-up transformer. In the circuit shown in Figure 2 a TRIAC 10 provided with an electrical supply 5 of 240 volts RMS at 50 Hz is triggered by a DIAC 12. The DIAC being powered from the supplies, the time delay comprising a resistor R1,variable resistor RV1 and a capacitor C2. The output of the TRIAC is connected to a discharge capacitor C4 in series with primary coil of a step-up transformer TS of the sectionally wound ferrite cored type. The various elements of the circuit are supplied through a choke L1 and capacitor C1 which are present to minimise radio frequency interference during operation of the apparatus. Operation of the circuit shown in Figure 2 is as follows. Repeated activation of the TRIAC by the DIAC causes the capacitor C4 to repeatedly discharge through the primary coil of the step-up transformer TS which produces a high voltage at output terminals XY of the secondary of the transformer TS. The frequency of the pulses emitted by the DIAC 12 can be adjusted by variable resistor RV1 and this in turn affects the discharge rate of the TRIAC 10. It will be noted that the output from the step up transformer TS is earth-free and voltages in excess of 100,000 volts at very low current levels can be achieved making the apparatus safe for use in schools. The capacitor C4 may be replaced by a series parallel arrangement of four similar capacitors to inhibit breaking down. Various modifications may be made without departing from the scope of the invention For example another pulse producing element such as a multivibrator may be used in place of the DIAC. The transformer need not be of the sectionally wound ferrite cored type although this is much to be preferred. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to whether or not particular emphasis has been placed thereon. Claims (filed on 16/6/83)

1. Electrical apparatus comprising a high speed chopping circuit operable to repeatedly discharge a capacitative element in series with a primary coil of at least one step-up transformer.

2. Electrical apparatus as claimed in Claim 1, in which the high speed chopping circuit includes a Triac.

3. Electrical apparatus as claimed in Claim 2, in which the high speed chopping circuit includes a Diac, the Triac being activated by the Diac.

4. Electrical apparatus as claimed in Claim 1, in which the high speed chopping circuit includes a pair of thyristors in back-to-back arrangement.

5. Electrical apparatus as claimed in Claim 4, in which the thyristors are activated by a Diac.

6. Electrical apparatus as claimed in Claim 4, in which the thyristors are actuated by a neon discharge tube.

7. Electrical apparatus as claimed in Claim 1, in which the high speed chopping circuit is operable from a D.C. supply and which includes a thyristor.

8. Electrical apparatus as claimed in Ciaims 1, 4 and 5 in which the high speed chopping circuit is operable from a D.C. supply and includes a diode.

9. Electrical apparatus as claimed in any preceding Claim, in which the transformer is of the sectionally-wound ferrite-cored type having a high resistance secondary to produce a high voltage at low current.

10. Electrical apparatus as claimed in Claim 3, in which there is provided a resistive/capacitive time delay element to adjust the frequency of the signal supplied by the Diac.

11. Electrical apparatus substantially as hereinbefore described with reference to the accompanying drawings.