LOLbooster Update: Overcurrent Protection Issues Pt. 2
The problem with the over-current circuit misbehaving turned out to be three separate issues, all of which were easy to track down and fix. First, the RC network that permits bursts of, e.g., inrush current without tripping the overcurrent protection was wired up wrong. Second, I did in fact need a voltage buffer. Third, a bypass capacitor on the current sense line was causing no end of problems. Short-circuit protection now works precisely as I’d hoped: Total current draw is limited to approximately 3A, although very brief bursts of current are tolerated, up to about 10A. Nevertheless,...
read moreLOLbooster 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: Input and Fault Detetction Stages
Here’s the final major piece of LOLbooster: input handling, and the logic for detection of a DCC signal and of faults in the booster. This entry completes the first round of the booster’s design, and what remains is to test it (already begun!), and design a PCB for the first prototype. Here’s what I hope to achieve with the input and fault-detection stages. Compliance with NMRA RP-9.1.2 Over-temperature shutdown. Auto-resetting short-circuit detection. Shutdown on loss of DCC signal. Here is the schematic to reference as I discuss how I’ve attempted to meet the...
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