I (mistakenly) thought that all X2222 variants would behave the same, such as the BT2222A (an SMD package) that I was about to order. basically it avalanches and continues being on until current drops to zero, then resets itself undamaged. I know the other part of that is a pwm driver, of course - but I want to be certain I knew exactly how much current is being sent and spent.I've been experimenting with a 2N2222 transistor (in the TO-18 metal case) and using it as an avalanche transistor - by not connecting the base and having the emitter and collector connected in reverse (so maybe I'm actually using the reverse mode, I'm not really sure). I was also interested in knowing this to better my skills in building a circuit to drive high intensity LEDs, control the power to give the most light without sending too much energy. But I got the circuit to work, I am not sure I'm doing the right thing, but it's not smoking or getting hot so far. I got confused because I just wanted to send +5v on or off to the power line, and not power the hc-05, and toggle a ground wire by a transistor. I started off to control the power-on to the hc-05, so I could reset the board into command or spp mode. The reason I am trying to do this, is for many reasons, mainly education so I can design better circuits. I guess if that energy isn't consumed by a device or resistor it's probably turned into heat and poof - goes the circuit. And I must have hit some type of limit because the transistor burnt out. I was playing around with that until the pot started smoking (lol not me).īut it seemed like the sweet spot was above 100k started limiting to the range I needed, but I had to keep giving it more 100k resistors for every 10 more ma of current to limit. Like it didn't seem to start limiting current until I put 100k ohm resistor in.
I think I noticed a sweet-spot in the circuit. And in fact, most real-world circuits (not just op-amp circuits) rely on the same principals so in production you don't have to tweak pots or select resistors. They have very-very high gain and with negative feedback the gain can be controlled with the resistors, and you don't have to worry about the exact open-loop gain of the "raw" op-amp. But, since there is so much tolerance in the transistor's gain, that's just a starting point. So, if the transistor has a gain of 100, we need 0.45mA through the resistor (and base) so that's about 11K. But, since the transistor's gain has such a wide range we don't need to be that exact and we can just assume 5V across the resistor. The base-emitter junction acts like a diode, so I'll estimate a voltage drop of 0.6V and that means with 5V applied you've got 4.4V across the base resistor. That's a wide range (typical for a transistor) so you either need a pot, or you can experiment and select a resistor, or design a more advanced circuit that depends on resistor values rather than the transistor itself.* According to the datasheet the PN2222 has a current gain (h fe) of between 50 and 375 depending on the conditions and the particular part.
0 kommentar(er)
