555 photographic exposure timer circuit

Published:2011/5/23 5:30:00 Author:TaoXi | Keyword: photographic, exposure, timer circuit | From:SeekIC

As the figure 17-8 shows, the timer uses the 555 as the core. If you press switch AN, the timing begins. You need to press AN to set the 555's trigger port,pin-3 has the high electrical level, the normally closed contact point of the relay will turn on the expose lamp. Then the C is charged through VT1 and RP. In order to make the charging voltage to keep the linear growth, we use the MOSFET 3DJ8 for the cross-flow charging. When C's charging voltage is higher than pin-6's threshold level 2/3VDD, 555 resets, pin-3 has the low electrical level.



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