LOLbooster 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 Update: Power Supply Design Issues
I got my bigger breadboards, and I began prototyping the bit of the design of which I am least confident: The voltage supply to the track. Recall that the design was meant to monitor the track voltage, and adjust the supply voltage to keep the track voltage steady, to compensate for voltage drops due to large loads on the tracks. The design I created reflected a fundamental misunderstanding of how adjustable voltage regulators work, and so failed. Unsurprising, really. But, what’s more, at some point I had two pins on the LM338 swapped, and, although it is hard to be sure, I may have...
read moreLOLbooster: Power Supply
Next up: The power supply. LOLbooster includes one 6V regulator for the various logic chips, but where most DIY designs defer track-level voltage regulation to the wall-wart, I’ve opted to include it on the board. Why? Because wall-wart regulators are very good at keeping a steady voltage—at the power jack. But we, finicky modelers that we are, want to keep a steady voltage not at the power jack, but at the rails. Which is an entirely different bucket of colored horses: It means we need regulation on the booster itself. Read on. 1 Nov 2010: Turns out the load regulation circuit below...
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