Power supply for scale model
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Project aim
An experimental power supply for scale model (train for instance).
This switching regulator improves low speed motion.
Tests with HO train scale models have been quite positive comparing with a standard supply using a linear regulator.
Schematic
Three main blocks :
- A curent source for a perfectly linear command,
- A RS flip-flop using the outputs of a comparator so that the voltage of the 10 nF capacitor is comprise between 10 and 90% of the power supply (5V).
- A darlington to have the required power.
Soldering
The circuit uses a 4 * 2 inches breadboard (see electronic blocks) quite close from a definite single side PCB.
I have used a double potentiometer because it was the only one in stock. A single one is sufficient.
The protection resistor (5,6 Ohm more than 10W) was as close as possible from the supplied circuit.
Trimming and measurements
The 20 kOhm potentiometer allows to trim the switching frequency between 0.7 à 14 kHz with a 10 nF capacitor. With a 1 nF one, oyou can trim between 7 and 140 kHz.
On the scope :
- Bottom trace, the (quite linear) signal on the 10 nF capacitor (2V/div),
- Top trace, the output signal with fast edges (5V/div).