LED Constant voltage Passenger car lighting using 7805 regulator circuit
Joined: Sep 25, 2010
Topics: 32 Replies: 39
Please read the first post for construction methods. For us conventional operators some of us do not like the intensity changes of lighting during operation. To get constant voltage lighting here we are going to use a voltage regulating circuit. The 7805 regulator chip when circuited will put out a consistent 5 volts DC whenever 6-24 volts is applied to it. Compared to circuit 1 this will use more wattage dissipated as heat generated by the regulator resisting current flow. The regulator acts as a variable resistor only allowing 5 volts to the lights. If light bulbs were used it would use a lot of wattage and be impractical. However with LEDs the circuit is practical and still uses considerably less than bulbs. A well lighted passenger car would use maybe 3 -4 watts at maximum voltage (18) and less and lower voltage typically 14 used on conventional layout speeds. Light bulbs can pull 8 watts per car or more and are not constant voltage. Normally the regulator will handle this without a heat sink.
This circuit can be mounted on fish paper,the regulator mounted to the bridge leads. Pin 2 is broken off and the regulator back,common with pin 2 is used as a connection point.
This circuit will also work in command mode,the only downside is the increased power usage. The circuit can be dimmed with a pot on the regulated side. DCS users would have to ad a choke (22uh). Note each LED needs a resistor as a current limiter. For dimmer lighting a larger value resistor can be used.
When mounting to metal roofed cars insulate the back with an additional strip of fish paper. For plastic roofed cars first glue some tin foil to the roof. This will dissipate the heat given of by the regulator and keep the roof from melting. The regulator back is what gives off heat.. Mount the regulator so it fits down into the bathroom or some other discreet place. Permatex high temp form a gasket sold in Walmart automotive works well.
here are photos of a car lighted with LEDs