MODEL_RAILROAD_LIGHTHOUSE_LAMP_SIMULATOR

Published:2009/7/17 3:39:00 Author:Jessie | From:SeekIC

The lamp turns on and off gradually, controlled by the charging and discharging of the capacitor. Here is a circuit that will do the job. It uses a TIP120 power transistor as a voltage-regulating element. The voltage across the lamp is always 1.2V lower than the voltage across the capacitor. Closing the switch charges the capacitor gradually over a period of a few seconds, causing the voltage to go up. When the switch opens, the capacitor slowly discharges and the voltage goes down again. You might have to experiment with component values to get the effect you want. The capacitor controls both the rise time and the fall time; the resistor controls the rise time only. In both cases, larger values make the action go more slowly. Be sure to mount the TIP120 transistor on a heatsink, and remember that its mounting hole is connected to the collector (and thus to +12 V in the circuit).



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