Power Supply Hardware Description

Refer to the Power Supply Schematic

The D&B model railroad control electronics requires 5 volt and 12 volt power. Initially, an old computer power supply was used. But the need for an adjustable 12 volt supply, low 5 volt current requirements and the desire for silent power supply operation (no fans) prompted its replacement by this power supply design.

The 5 volt power is used by the Basic Stamp modules and their associated logic circuits. The 12 volt power is used for the twin coil switch machines and is adjustable from about 10 to 14 volts. The voltage adjustment provides for the balancing the voltage for reliable turnout positioning and the minimizing of switch machine noise.

Both power supplies utilize AC/DC adaptor modules for conversion from AC line voltage to DC. The adaptors were obtained from Newark Electronics. The 9 volt adaptor that is used for the 5 volt power supply is WDU9-1200 (Newark p/n 97F7921). The 15 volt adaptor that is used for the 12 volt power supply is WDU15-1000 (Newark p/n 97F7927).

The DC voltages are further conditioned using LM350 variable voltage regulators. The 120/430 ohm resistors set the 5 volt regulator output voltage. The 120/820/1000 ohm resistors set the 12 volt regulator output voltage.

The LM350 regulators must be heat sync'd. This can be easily accomplished by enclosing the regulators and their associated components in a metal project box. Attach the regulators to the box using appropriate insulators and thermal compound. The resulting power supply system is very compact.

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Copyright © 2006 Don Buczynski
San Diego, California