LOLbooster Update: Overcurrent Protection Issues
Having abandoned the track-level voltage regulation, my recent testing has centered on the short-circuit and over-current protection. These tests are fun, as they involve loading down the booster as heavily as I can (a combination of 12V bulbs, LEDs, and non-DCC motor cars can get me to about 2A, according to my multimeter). I’ve found that the present configuration is not very tolerant of inrush currents, refusing to light more than about eight 50mA bulbs at once (since my multimeter is very slow, I can only guess that represents about 4A of inrush current); five if there are any...
read moreLOLbooster Update: Power Supply Design Issues Pt. 3
After struggling all weekend with the problem of regulating the track voltage, I’ve decided to simply remove this feature from LOLbooster. The fact that the LMD18200 shuts down when its voltage input drops below 10V presents a problem too difficult for me to surmount. Perhaps later, I will design a more advanced booster that uses discrete switching elements that will permit relatively easy track voltage regulation, but for the sake of my own sanity, and to keep the project manageable, such will have to wait. I’ve got nearly the rest of the booster breadboarded, with only the...
read moreLOLbooster Update: Power Supply Design Issues Pt. 2
A little fiddling on the breadboard revealed some interesting results. The LMD18200 shuts itself off when the input voltage falls below 10V, as a safety precaution perhaps. When this happens, if the LM338 voltage regulator is monitoring the LMD18200 outputs, and the LMD18200 is shut off (because, e.g. of a fault condition, or because I shut it off manually), the voltage on the outputs becomes 0V, and the LM338 output falls to about 3–4V. And stays there. No matter what. Re-enabling the LMD18200 does nothing, nor does twiddling the adjustment trimpot. The whole system has to be reset. The...
read moreLOLbooster: Output Stage (Part 2)
Having selected the LMD18200 as the h-bridge driver for the LOL booster, what remains in designing the output stage is to select a heatsink, and to draw up the auxiliary circuitry.
read moreLOLbooster: Output Stage (Part 1)
Learn more about the LOLbooster, and purchase PCBs and kits. The output stage of a DCC booster is basically a class-D amplifier output stage. It takes the processed DCC signal, a square-wave signal of approximately 15KHz, and pumps it to the specified output voltage (~12Vp for N scale, less for Z and more for HO) and current (as required by what’s on the track, up to the specified maximum). Unlike audio signals, however, DCC signals are differential-mode—whatever signal is put onto rail A is mirrored and inverted on rail B. So, a booster output stage uses two push-pull amplifiers in...
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