These circuits can be used to supply low current DC accessory circuits by tapping into the DCC track supply Bus. This might be done if a regular DC supply was not available and the power required by the accessory was small.
The unregulated power supply circuit could be used to supply power to the Automatic Grade Crossing circuit on this site.
WARNING - Accessories supplied by these circuits must not share common electrical connections with circuits connected to other power supplies, either DCC or AC powered. Any inter-connections with other circuits should be through optoisolators or relays to prevent possible short-circuiting between the supplies.
The next diagram shows the effect of rectifying a DCC voltage with a full wave bridge. The voltage at the output of the bridge is equal to the input minus the drop across the diodes.
The small tick in the output of the bridge occurs when the polarity of the H-Bridge reverses. The size of the ticks is largely determined by the efficiencies of the H-Bridge and rectifier bridge and in most cases can be ignored. This is why filter capacitors are not needed for decoders.
Diodes used to rectify DCC should be Schottky or high speed silicon types. Diodes of the 1N4000 and 1N5400 series are not suitable for this application due to their slow turn-off times.
The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.
If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.
Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.