> I am running lego brand trains (a 9v system) and feel like the power
> supply could be made much better.
> currently, it's a very simple LM317T circuit with 6 resistors.
> my problem is that at the low speed, under heavy load, the train has
> troubles moving at all.
> what solutions would be open to me ?

The normal "improvement" is a pulsed supply that provide full voltage for a
varying period - ie PWM. The theory is that high resistance contacs such as
tracks to wheel, engine brushes/comms (if still used) switch contacts etc
are broken down by the application of full voltage.

You could perhaps adapt a 317 based supply to this by simply applying PWM
via suitable resistors to the 317 control terminal. Supply goes from full to
low voltage each PWM cycle. A 317 based supply will not go to 0 volts unless
something is done about the smallest possible output voltage from the 317. A
few sries diodes is a crude but probably effective enough way to do this.

There are sure to be PWM based controller circuits on web. Ask Google.
There's one here http://www.simmstick.com/entries-.htm as part of the
simstick competition.



        RM

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