The LT3420/LT3420-1 are high voltage photoflash capacitor chargers with automatic refresh. They are designed for use in both digital and film cameras and use a flyback topology to achieve efficiencies up to four times better than competing flash modules. A unique adaptive off-time control algorithm maintains current-limited continuous mode transformer operation throughout the entire charge cycle, eliminating the high inrush current often found in modules. The LT3420/LT3420-1 output voltage sensing scheme indirectly regulates the output voltage by monitoring the flyback voltage, eliminating the need for an output resistor divider or discrete zener diode. This feature allows the capacitor to be quickly charged to 320V from a 5V input voltage, making it suitable for any size photoflash capacitor.