High Voltage, Low Current Supply
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 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. The details of the transformer windings are given in the Table.
In 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 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
Title: High Voltage, Low Current Supply
electronic circuit
Source: www.electronic-circuits-diagrams.com
Published on: 2005-02-01
Reads: 979
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