In low light conditions, high-end equipment for film or digital photography requires a xenon flash tube for shooting. The Xenon flash tube provides an instant high-intensity light source, which is the most basic requirement when shooting objects that are far away, moving at high speeds or in low light conditions. This spectrum produced by the xenon discharge tube is very close to the spectrum of the sun, providing very accurate color reproduction.
Once the trigger signal is applied, the xenon flash requires a high voltage on its electrodes (typically, the voltage is approximately 300V) to flash. All the energy needed for flash is stored in a large capacitor called a "flash capacitor." Once the flash is triggered, all of the energy stored in the flash capacitor is released through the flash tube to produce the source. These energy stored in the flash capacitor are provided by a dedicated boost converter that charges the flash capacitor from a very low battery input voltage up to 300V. In the past, such converters were made up of large discrete components that were difficult to integrate into small devices such as cameras.
TI's TPS65552A greatly simplifies design and reduces the size of the camera flash charger circuit. Figure 1 shows a flash capacitor charger based on this device. The TPS65552A provides all the necessary charge control, output feedback, charge completion status, insulated gate bipolar transistor (IGBT) drivers, and some circuit protection necessary to implement a small, efficient flash charger.
Figure 1 TPS65552A Camera Flash Capacitor Charger
The TPS65552A is based on a reverse topology. It can sense the output voltage during the internal switch disconnection. During this time, the output voltage is reflected back to the input through the transformer. This eliminates the need for a large volume, high voltage feedback network at the output and also provides electrical isolation from the input to the output. Once this output voltage reaches its target value, the TPS65552A automatically stops charging while the open collector output is degraded, giving a “flash ready†status signal. This output can drive an indicator status LED, or the I_PEAK pin of the TPS65552A controls the peak current flowing through the primary winding of the reverse transformer T1 during all switching cycles. To adjust the capacitor charging time, the main current can be dynamically adjusted from 0.9A to 1.8A by changing the voltage applied to the I_PEAK pin. This feature allows the microcontroller to dynamically control the charger's current flow for power management. For example, in a digital camera, the microcontroller can reduce the charger current while the high current zoom motor is operating, so that the zoom motor and charger can function simultaneously without exceeding the maximum current capability of the camera battery (see Figure 2). ). This feature can also be used to extend battery life. Reducing the peak current during charging also reduces the average current consumption, allowing the low-capacity battery to charge the flash capacitor.
Figure 2 Complete camera flash module with power management and flash management
In the past, the flash was triggered by a push button switch or a silicon controlled rectifier (SCR). However, the updated flash mode (for example: red-eye reduction mode) uses multiple xenon lights to expose. The flash is triggered for a short flash that does not completely discharge the camera flash capacitor. Thus, after a short delay, the flash is re-triggered for the main flash. The button and SCR cannot reliably start and stop the flash intermediate flash. The IGBT is capable of handling currents typically 150A during flash. However, like MOSFETs, the IGBT gate requires a large current pulse to turn on quickly; therefore, a high current driver is required.
The TPS65552A has an integrated high current buffer to drive the IGBT gate used in the trigger circuit. During flashing, the IGBT gate can be driven on and off to support flash modes such as red-eye reduction or to evaluate the IGBT gate through a lens (E-TTL).
Table 1 List of typical parts of the circuit in Figure 2
Nomex Self Closing Sleeve,Nomex Split Braided Sleeve ,Nomex Self Closing Wrap,Nomex Cable Protection Sleeve,Nomex Split Cable Sleeve
Dongguan Liansi Electronics Co.,Ltd , https://www.liansisleeve.com