High Voltage Generation For Xenon Tube Applications

Introduction The ignition Timing lights in common use range from simple neon to complex units. Neon Timing lights have a drawback that due to their low light output, the user is forced to operate them in subdued lighting. This becomes a safety hazard as one tends to hold the unit close to the Timing mark and to the “invisible” (or apparently stationary) fan blades. The ignition lights which use Xenon filled stroboscopic tubes are much better, since their light output is of much higher intensity. The circuit described in this note incorporates such a tube, which has an anode voltage rating of 500 volts maximum and requires a trigger voltage between 2-6kV. The circuit was designed for a four stroke engine. It will be seen later that the unit CAN be converted for use as a low power stroboscope with some slight modifications. The required high voltage for the tube was achieved by using an inverter. The inverter must drive a capacitive load and also withstand the secondary being shorted. Operating the inverter in the flyback mode seemed the best choice, since the energy transfer only takes place when the switching Transistor is off, thus effectively isolating it from the load. Circuit Action In the circuit diagram shown in Figure 1, the Transistor Tr7 is the switching device. The transformer T1, converts the voltages and also transfers the energy. The capacitors C10 and C11 are used as energy storage elements. When the tube is triggered, this stored energy is discharged into the tube - which produces a bright Flash of light. The brightness of the Flash depends on the size of the storage capacitors and the voltage to which they are charged. The switching of Tr7 is controlled by the Schmitt Trigger formed by Tr3 and Tr4, which senses the ’current’ through the primary and secondary. On Switch on, the Transistor Tr3 will be off and Tr4 will be on. Thus, turning on Transistor Tr5 pulls the Gate of the MOSFET Transistor up to approximately the supply voltage. Whilst the MOSFET is on, the energy is stored in the primary inductance of the transformer. The current in the primary increases as a linear ramp whose slope is inversely proportional to the primary inductance. The resistor R11 senses this
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High Voltage Generation For Xenon Tube Applications application circuits
High Voltage Generation For Xenon Tube
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