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Miniature Strobe
Light |
| Strobe lights are widely used by disco lovers to
create wonderful visual effects in disco halls and
auditoria. The circuit of a battery operated portable
miniature strobe light, which can be constructed using
readily available inexpensive components, is described
here. For convenience and simplicity, an ordinary neon
lamp is used here in place of the conventional Xenon
tube. The whole gadget can thus be easily accommodated
in a small cabinet, such as a mains adaptor cover, with
a suitable reflector for neon lamp to give a proper
look. Since current requirement of this circuit is very
small, it may be powered by two medium-size dry cells
(3V) or Ni-Cd cells (2.4V). Transistors T1 and T2 in the
circuit form a complimentary-pair amplifier. When switch
S1 is momentarily depressed, the circuit oscillates
because of the positive feedback provided via resistor
R2 and capacitor C1 to the base of transistor T1. The
sharp pulses in the secondary winding induce a high
voltage in primary winding of transformer X1, which in
fact is a line driver transformer (used in reverse)
which is generally used in 36cm TV sets. High voltage
pulses induced in primary side are rectified by diode D1
and rapidly charge reservoir capacitor C2 to nearly 300V
DC. When switch S1 is released, capacitor C2 holds the
voltage level for a finite period while capacitor C3
charges slowly through resistor R3. When voltage across
capacitor C3 becomes high enough, neon strikes and the
capacitor rapidly discharges through the lamp. When
voltage across capacitor C3 falls below the
extinguishing potential of neon lamp, it goes off and
capacitor C3 starts charging again. This cycle keeps on
repeating for a short time, based on the reservoir
capacitor C2’s value. Precautions. The neon lamp flasher
section of this circuit carries dangerously high
voltages. All precautions should therefore be taken for
protection. Before any repair work, discharge capacitor
C2 using a short length of wire with a 100k resistor
connected in series.
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