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• Danger here be rabbitholes...

  RW • 12/23/2020 at 04:59 • 0 comments

   The research has been getting a little off track, exploring the wonders of buck boost converters on RFID tags, there's a number of fascinating papers. I also went a little deep on transistor specs, trying to figure the whys of speccing certain transistors over others. I more or less concluded what I should have suspected, popular transistors are popular because they have middling specs in their range of competence, allowing a variety of applications for minimal number of separate SKUs in the parts box. i.e. boringly average parts that were "good enough", enough hFE, enough Veb enough Vce enough Ice and a Fmax way higher than you're screwing with. However, I'm wondering if I want to take that gamble on top of someone already taking that gamble, to whit, the possible blatant lies on a probably decade old at least RadioShack pack of assorted NPNs, which claims hFE 200 Vce 30V, Ice 800mA, dissipation 1.8W ! (Seriously has anyone seen anything in a dinky little T0-92 rated at more than fractional watts?) Playing part number bingo as I rattle them round in their little plastic bubble, I recognized a real 2N2222 and a BC546 but the others may have custom or more obscure numbers. Sure the 2N2222 in a T0-92 might handle 800mA and 30V but it's only supposed to dissipate half a watt, and has a rated min hFE of 100 which is a little short of 200. The BC546 we might hope is moving the right way with a bit more at 110, but then we're similarly disappointed with the 0.5W dissipation and YIKE, 100mA collector current. Though voltage is rated at 50, so is that 100 at 50, dissipation limited, and we get like 200 at 25 or 400 at 12.5?? Well it's still short of 800 at 30. Are we to believe these are "golden sample" hand picked dies that exceed spec? I doubt it. 

  But I wonder if I wander from the point, take the junky stuff, make it work. I do have a feeling I might be swapping transistors around on the breadboard though, "You don't need to handle 800 here, you're only seeing 150, you go over here, where this little guy is sweating his ass off trying to hold  350..." Gen-you-ine junk has turned up too, a microwave front panel board with 11 identical 2SC1815s on, at least I know what they are. I guess the generic "component tester" gizmo is going to see a lot of tryouts though. 

  I went nuts for an hour turning adafruit's site inside out trying to refind this article to illustrate the simple method of turning the RS-232 the right side up again with a transistor, but as you see, it's on sparkfun, derp, 

  https://www.sparkfun.com/news/2461 

  But after continued ponderation, and the discovery of two 4011s when I turned out my baggie of junky ICs looking for 555s, it seemed like it would be nicer/neater/more-parsimoniouslyistical (unlike that word) to use half a 4011, two nands as the oscillator for the buck boost, and wire the other two as inverters... This is provided one oscillator has enough oomph to drive two converters as we need negative volts as well... in which case either we use 2 oscillators and go back to a transistor logic inverter, or an additional drive transistor. 4011s are pretty common as a bit of glue logic on various computer boards, you even see them on HDDs up to about 2005ish. So I don't THINK I'm committing the magic chip sin here. However, tomato tomato, I'm trying to detail how this is a collection of blocks, swap in another block of the same function, oscillator, and you'll get the desired result. 555 or astable multivibrator, other logic oscillators, even 741s and other op amps can be made to squeal (If you poke them just right with a hot soldering iron! muhuhahahaaa) actually, audio engineers and RF bods are often trying to get rid of unwanted oscillation so if it intimidates you, just think of it as a fault you're causing to happen. I did in fact regard a nand oscillator as an anomaly until recently, like...

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