Page 31 - 39. MRH13-05-May2013
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Using Ohm's Law
Looking at what’s on that little board
A
fter my March 2013 Staying' Alive column
),
I got an e-mail from a fellow model railroader about
adding a battery to his camera car to keep the video from
dropping out with track power disruptions. He provided
me with a complicated circuit with two adjustable voltage
regulators and a bunch of capacitors and resistors.
I took on designing a simple module to charge the battery and
power the camera using DCC track power. The battery will take
over running the camera when track power is interrupted.
There are lots of needs in DCC model railroading for such
a circuit. They can provide power for coach lights or other
lighting details, on-board sound modules, etc. That’s why I
decided on making it a column.
Building such a device is a simple project, once you have a
design. So, I broke the circuit down into functional bocks
and designed each block, using Ohm's Law. A walk through
DCC Impulses column
by Bruce Petrarca
Let’s go from theory to circuit, step by step ...
DCC Impulses Column - 1
the design may help folks unravel some of the "mystery" of
electronics.
Functional blocks
There are three functions that this circuit needs to perform, as
shown in figure 1.
Power supply
Camera power
Battery charger
So, let's look at each function by itself and understand how to
select each component.
Power supply
This will turn the track DCC into a DC voltage. The DC voltage
will be slightly less than what the track DCC voltage is set to.
The schematic is shown in figure 2.
The heart of this function is the bridge rectifier – the four
diodes near the middle of figure 2. It stacks all of the posi-
tive DCC pulses on one side and all the negative ones on the
other side. It can come as a module with four terminals on it
1: Block diagram.
1
MRH-May 2013
