A flash cycle in the context of electronic circuits typically refers to a rapid and repetitive sequence of events, often involving the flashing or blinking of an LED (Light Emitting Diode). Flash cycles are commonly used in applications like warning lights, indicators, and decorative lighting. The circuit that controls this flashing sequence is called a flasher circuit.
- +Vcc: Positive supply voltage.
- R1: Base resistor for the transistor (controls the base current).
- C1: Capacitor (stores and releases charge to control the flashing rate).
- LED: Light Emitting Diode (flashes on and off).
- B|>: Symbol for the Base-Emitter junction of an NPN transistor.
- R2: Current-limiting resistor for the LED.
- GND: Ground connection.
How it Works:
- Charging Phase: When power is applied, C1 begins to charge through R1 and the base-emitter junction of the transistor. The transistor is initially off, so the LED is off.
- Discharging Phase: As C1 charges, the voltage across it increases. When the voltage reaches a certain threshold, the transistor switches on, allowing current to flow through the LED, causing it to light up.
- Capacitor Discharge: As C1 discharges through the LED and R2, the voltage across it decreases. When the voltage drops below a certain level, the transistor switches off, and the LED turns off.
- Cycle Repeats: The cycle then repeats, causing the LED to flash on and off periodically.
Photographs are images obtained by optically transferring object images onto light-sensitive films. Adequate light is crucial to clearly capture the object’s image on the photosensitive material. Artificial light sources used in photography are known as flashes.
Flashes utilize two-electrode lamps placed within a glass body filled with inert gases and displaced by air. These lamps operate at voltages ranging from 300-400 V. A third electrode, called the auxiliary electrode, is positioned in the body to initiate light emission. When voltage is applied, electron movement between the electrodes produces intense light.
During photography, these flashes emit high-intensity light for a duration of 1/500 to 1/5 seconds. Flash operation relies on high DC voltage generated by converter-like circuits, stored in capacitors. When the camera’s shutter button is pressed, the capacitor’s charge energizes the flash lamp’s electrodes.
The input DC voltage is converted into high-frequency AC using a simple transistor oscillator circuit and applied to the primary coil of a transformer. Variable currents in the primary coil generate high-value AC in the secondary winding. Diodes are used to transform this AC into the necessary high DC voltage for flash operation. The flash is ready when the neon lamp lights up.
Upon pressing the shutter button, rapid reduction of primary current in another transformer generates a high-voltage pulse in its secondary winding. This pulse ionizes the gas in the flash lamp, initiating current flow through the electrodes and producing intense light.