Electricity: electrical systems and devices – Safety and protection of systems and devices
Patent
1987-05-18
1990-01-30
Jennings, Derek S.
Electricity: electrical systems and devices
Safety and protection of systems and devices
307108, 307641, 307639, 328 67, H02H 300
Patent
active
048977535
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to an electric circuit which provides protection to a power source supplying power to a load through a resonant circuit. In such ciruits a cyclical operation takes place in which a direct current power supply charges a capacitor and the power stored in the capacitor is then discharged through the load. The discharge supplies operating power to the load and the present invention applies in particular to a load which needs repetitive discharges over an extended period or for continuous operation.
In such circuits the discharge of the capacitor through the load can be initiated by a switch device which connects the fully-charged capacitor across the load. At the appropriate time it is necessary for the switch device to become open circuit so that the capacitor can recharge and the regular operation of the circuit requires that this should occur.
If the switch device fails to become open circuit it effectively presents a short circuit to the power supply and unless the switch becomes open circuit within a predetermined time, the protective circuits of the power supply will cause the power supply to switch off to prevent it being damaged. The present invention provides a protective circuit to prevent just such an occurrence.
SUMMARY OF THE INVENTION
According to the invention there is provided an electrical circuit comprising first capacitive means arranged to be charged from a power supply, switch means arranged to close for discharging said first capacitive means through a load and then to open to enable said first capacitive means to re-charge, characterised in that second capacitive means are connected across said switch means and current limiting means are arranged in the circuit between the power supply and said second capacitive means, whereby upon continued closure of said switch means said second capacitive means first discharges through said switch means and then applies a reverse voltage to said switch means causing opening of said switch means.
Preferably, said power supply is prevented from charging said second capacitive means in the event of continued closure of said switch means by said current limiting means.
Preferably also, means are provided for discharge of the energy in said current limiting means.
Preferably also, a detector is arranged to indicate if operation of said circuit occurs in excess of a predetermined rate.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:-
FIG. 1 is a circuit diagram for a laser discharge resonant circuit constructed in accordance with the invention, and
FIGS. 2 to 4 are voltage and current wave form diagrams.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring first to the circuit outside (to the left and right of) the two broken lines of FIG. 1, there is shown a capacitor C1 arranged to be charged from a direct current voltage supply V0. When voltage V0 is applied current flows through inductor L1 and diode D1 to charge capacitor C1. The voltage V1 (FIG. 2) across capacitor C1 rises towards V0, the current I1 (FIG. 3) reaches a maximum and starts to decay. Inductor L1, which initially resists the current I1 flowing when voltage V0 is first applied, now resists decay of this current with the result that the voltage across capacitor C1 continues to rise and eventually reaches twice V0.
At time t1 thyratron T closes and connects capacitor C1 directly across the load. The load in this case is a pulsed metal vapour lase using a material such as copper as the vapour lasing medium. The charge which has been developed across capacitor C1 causes a discharge to travel down the discharge tube of the laser initiating lasing. Normally thyratron T then becomes open circuit after a short period and capacitor C1 is then recharged from the d.c. power supply. This mode of operation continues at a pulsed repetition rate of about 20 KHz.
Capacitor C2 is connected across the power supply for smoothing purpose
REFERENCES:
patent: 3881120 (1975-04-01), Osterwalder
patent: 4684820 (1987-08-01), Valencia
"A High-Power Current Pulse Generator", Instruments and Experimental Techniques, vol. 25 (1982), Jul.-Aug. No. 4, Part 1, pp. 884-886.
"A Pulse Circuit for Excitation of a Partical Accelerator Electromagnet", Instruments and Experimental Techniques, vol. 17, No. 6, Part I, Nov./Dec. 1974, pp. 1563-1564.
"Simple Capacitor Charging Power Supply for a 100-pps Laser Pulser", Review of Scientific Instruments 56 (1985), Mar., No. 3, pp. 382-384.
Kearsley Andrew J.
Naylor Graham A.
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