Ignition monitor strobe

Figure A shows the circuit of a direct-trigger timing light. The trigger voltage is -taken from the car's ignition circuit by a direct connection to a spark plug. A circuit using an inductive pickup is shown in Fig. B. A trigger transformer is used to develop the high-voltage pulse for triggering. The triggering circuit consists of Tl, CI, SCR1, inductive pickup coil T2, and the waveshaping components in the SCR's gate circuit.
Ignition monitor strobe - schematic

When the spark plug fires, it induces a pulse in pickup coil T2 that triggers the SCR gate. The SCR fires and discharges C2 through the primary of Tl. The secondary of Tl feeds a high-voltage pulse to the trigger electrode of the flash tube. That pulse causes the gas—usually neon or xenon—to ionize. The ionized gas provides a low-resistance path for CI to discharge, thereby creating a brilliant flash of light. Resistor Rl limits current from the supply as the tube fires. When CI is fully discharged the strobe tube cuts off and returns to its ' 'high-resistance'' state. The current through R2 is not enough to sustain conduction through SCR1, so it cuts off and remains off until it is re-triggered by a gate pulse.

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