22 February 2012

App Note 95

Simple circuitry for cellular telephone/camera flash illumination: A practical guide for successfully implementing flashlamps. 12 pages.

This short little app note with a long title discusses the LT3468, which is a monolithic power-converter chip for driving camera flashtubes. As Figure 1 testifies, flashlamps are much brighter with better color temperature than LEDs, and so are the preferred illuminator for digital cameras. After a brief discussion of the physics, Jim discusses the support circuitry and construction requirements. "Capacitor, wiring and lamp impedances typically total a few ohms, resulting in transient current flow in the 100A range."

This app note contains a single application schematic, shown in Figure 6. Most of the text is dedicated to measurements of the circuit performance (Figures 7 to 10). Figures 9 and 10 are particularly interesting, with vertical scales of "relative light per division". Surprisingly, Jim does not reveal how he made the "relative light" measurements.

A carefully worded caution appears near the end of the text:
In cases where the lamp is triggered with a user-selected transformer and drive scheme, it is essential to obtain lamp vendor approval before going to production.
That quote sounds like the voice of unfortunate experience.

The app note ends with a cartoon. "Nice seeing you again. Yeah, nice seeing you again, too."

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