What is a flash?:
Photographs are images obtained by projecting objects onto light-sensitive films. In photography, it’s essential to have an adequate light source to effectively capture the object’s image on photosensitive material. In this context, the artificial light sources utilized during photography sessions are commonly referred to as “flashes.”
These flashes employ dual electrode lamps enclosed within a glass body filled with inert gases. The lamps operate at voltages ranging from approximately 300 to 400 volts. Additionally, a third electrode, known as the auxiliary electrode, is positioned within the lamp to initiate the emission of light.
This auxiliary electrode extends through the tube and terminates near the edges of the primary electrodes. When voltage is applied to the lamp, the discharge process commences, resulting in the emission of intense light due to electron movement between the electrodes.
High-intensity flashes, used for photography, typically have exposure times ranging from 1/500 to 1/5 of a second. To provide the high DC voltage necessary for flash operation, circuits resembling converters are employed. This voltage is stored in capacitors, and when the camera’s shutter button is pressed, the load from the capacitor is discharged onto the electrodes of the flash lamp.
In the provided circuit, a DC voltage is applied to the input, where a simple oscillator circuit featuring a transistor converts it into high-frequency AC. This high-frequency AC is then directed to the primary windings of the transformer (TR1). Variable currents coursing through the primary windings of TR1 produce a substantial AC output in the secondary winding. High-voltage diodes are employed to extract high voltage from the secondary winding, providing the requisite high DC power for flash operation. A clear indication that the flash is primed for operation is when the neon lamp emits light.
Upon depressing the shutter button, the primary current within the TR3 transformer rapidly diminishes to near zero. This swift decrease generates a high voltage in the secondary winding of TR3. This voltage affects the central electrode, often referred to as the auxiliary electrode, within the flash lamp, leading to ionization. The ionization of the gas within the tube initiates the flow of current between the two ends at the edges of the lamp, culminating in the emission of intense light.