Ahigh voltage power supply is a very useful source which can be effectively used in many applications like biasing of gas-discharge tubes and radiation detectors etc. Such a power supply could also be used for protection of property by electric charging of fences. Here the current requirement is of dc power supply the order of a few microamps. In such an application, high voltage would essentially exist between a �live� wire and ground. When this �live� wire is touched, the discharge occurs via body resistance and it gives a non-lethal but deterrent shock to an intruder. The circuit is built around a single transistorised blocking oscillator. An important element in this circuit is the transformer. It can be fabricated on easily available ferrite cores. Two �E� sections of the core are joined face-to-face after the enamelled copper wire wound on former is placed in it.

PIn this configuration, the primary winding and the feedback winding are arranged such that a sustaining oscillation is ensured once the supply is switched on. The waveform�s duty cycle is asymmetrical, but it is not very important in this application. Please note that if the oscillations do not occur at the �switch-on� time, the transformer winding terminals of the feedback or the primary winding (but not both) should be reversed. The primary oscillation amplitude is about 24V(p-p). This gets amplified with the large step-up ratio of the transformer and we get about 800V(p-p) across the secondary. A simple series voltage multiplier (known as Cockroft-Walton dc power supply circuit) is used to boost up this voltage in steps to give a final DC of about 2 kV. The output voltage, however, is not very well regulated. But if there is a constant load, the final voltage can be adjusted by varying the supply voltage.

The present configuration gives 2 kV for an input DC voltage of 15 V. Though higher voltages could be achieved by increasing input supply, one word of caution is necessary: that the component ratings have to be kept in mind. If the ratings are exceeded then there will be electrical discharges and breakdowns, which will damage the device