Safety flare

Posted on Apr 7, 2012

When SI is on, power is applied to an oscillator composed of Ql, Rl, Cl, LI, and L2. Coil Ll is the primary winding of Tl, and L2 is the feedback winding. When Ql turns on, its collector current saturates Tl's ferrite core. That, in turn, removes the base drive to Ql through L2. Transistor Ql then turns off. As the field around Ll and L2 decays, Ql will eventually turn on again, and the cycle repeats over, and over. Transformer Tl is a step-up, ferrite-core, potted-type unit whose secondary-winding (L3) output is rectified by D2 and filtered by C2, That capacitor charges up to around 250 to 300 volts, which is applied to the resistor divider composed of R3 and R4, along with the flash tube FX1.

Safety flare
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Capacitors C3 and C4 will charge up to around 200 and 100 volts, through R3 and R4, respectively. Flash rate is adjustable via R4. When the charge on C4 gets to around 100 volts, neon lamp NE1 fires discharging C4 into the gate circuit of silicon control rectifier SCR1. The SCR1 turns on discharging C3 into the primary winding of trigger-pulse transformer T2. Transformer T2 is another step-up, pulse-type unit providing an output of around 4 kW across transformer T2's secondary winding. The xenon gas inside FX1 is ionized and a bright flash is emitted. Finally, C3 quickly discharges through L4, and the cycle repeats over, and over.

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