Jump to content
Electronics-Lab.com Community


  • Content Count

  • Joined

  • Last visited


Everything posted by flippityflop

  1. so it's Ve = Vc - Vbe? ok... i missed that from just reading from wikipedia... i read the voltage on the load is *mostly* is constant for most of the operating current range... then again the examples from wikipedia has the load on the collector side... collector side, then...
  2. well, emitter in saturations is still slightly bit higher... (Ie_sat = Ib_sat * (1 + hfe))
  3. answering my own question again: it just struck me, but maybe the capacitor was not charging not because of properties of currents in collector and emitter for any NPN, but because i've been thinking in terms of conventional current... Let: Q be a sub-circuit of an avalanching transistor and capacitor in parallel. in my case, the avalanching transistor is 2N2222; the "generic NPN" is not the 2N2222 mentioned. whenever Q was in the emitter side of the generic NPN, the negative terminal of the Q's capacitor is already in the highest negative charge. the momentary opening of the gener
  4. i'll solve the specific circuit problem on my own... although, i would like an answer on the first question... when switching, is it better to go with the emitter on NPNs and the collector on PNPs?? do their electrical characteristics differ more than slightly higher currents?
  5. i'm asking as i've been working on a design that to my understanding should've worked. i have a generic NPN restoring the supply voltage and feeding it's emitter output to a 2N2222 parallel to a charging capacitor for a delayed avalanche. somehow the avalanching only works when i swap the 2N2222 + charging capacitor sub-circuit to the collector side. it surprised me as when it was connected to emitter, it was also directly connected to ground. and when it was on the the collector side it was directly connected to the supply. so it was not isolated and would be biased to a common ground. altho
  6. alright, continuing the series... another question i would like to as is on NPN BJTs, would it be better to put the load on the collector side or the emitter side?? in schematics, i almost always see it on the collector side (Ic = hfe * Ib), but the emitter side also works and when doing plain switching (in saturation) the emitter side works at least as well (Ie = Ib * (1 + hfe))... so would there be any difference? the same with PNPs, when it comes to switching, would the collector side (Ic = Ib * (1 + hfe)) work better than the emitter?
  7. i need to know what is the lowest current that is reliable for cases such as: a.) charging a capacitor b.) when the current is being read by an instrument such as an ammeter c.) logic signals what i mean is that even outside normal conditions -- exposed to hot summers and cold winters, being touched by bare hands when testing, or when it's humid, etc -- what are the minimum low currents that will cover a, b, c above?
  8. are these NPN BJTs: http://pdf1.alldatasheet.com/datasheet-pdf/view/17918/PHILIPS/MMBT2222A.html the same as those 2N2222 that has been around for since forever? can i trust that the reverse active and avalanche breakdown profiles are the same??
  9. ok i actually just realized the flaw after i last posted. i thought of mentioning it, but i thought it will have you guys think that i am trolling. (i actually just checked again for additional posts from you guys) yes, hero999 there needs to be a common ground here for this to be a universally applicable (aside from the aforementioned caveat that you have to balance the R1 and R2). to see why, we need to visit what was posted in this thread (hence my fear of this being seen as trolling): http://www.electronics-lab.com/forum/index.php?topic=39704.0 basically, V1 and V2 are just voltage dro
  10. i was wondering why is it, for just half duplex systems, don't we have a dedicated transceiver and a dedicated transmitter antenna. ok, just hear me out... assuming we are using grounded monopoles, we can have a resonator connected to a diode whose anode is connected to the transmitting antenna, and have a receiving second antenna connected to the cathode of another diode then going to the resonator. the transmitting and receiving antennas would also be made of different materials that are nonreciprocal. ferrites that are biased to transmitting and receiving (higher gains). since they're h
  11. you know what i'm talkin' about... anyways, just in case somebody stumbles upon this simple thread in the future, i'll attach a more concise diagram:
  12. also, why i am convinced that sometimes it might be helpful to consider "pulls" is that i see a lot of voltage supplies apparently provides negative voltages.
  13. ok, i guess i lose here... in all cases "conventional current" and the idea of 0V grounding that comes with it abstracts all cases when it comes to passive components. in active components as long as it is only immediately in series with a passive component, then it *should be safe*. if 2 or more active components are in series, then i'd still raise questions if it could work. ok, look at the attached diagram and apply conventional current and see if we can make it all work. suppose the 2 identical avalanche diodes in series with a active component "Q". we also define an "ambient" voltage
  14. no, i was reffering to a "passive" comparator, sadly also being a very limited one. there's very little voltage drop and current used in your "active" comparator... it's something very discrete that can be added with very little effect to the rest of the original circuitry. mine is something that comes up not very often, but a cheap one if it ever does. you'd hardly come across R1 and R2 that are equal. maybe you can readjust the rest of the original circuits, so that they are, but there's no guarantee it will work out. probably where we can see this arise often is when we tap this onto vol
  15. uhhh... nobody's explaining this satisfactorily... c'mon... i need to know so i can ask further questions about semiconductors and VH electronics... EDIT: "VH speed electronics" forgot the "S"
  16. so, looking at the attached diagram, is there a "pull" on the cathode side of the capacitor or a push from the other side?? or both? if it's a little hard to explain, then tell me how it happens in actual physics, not in conventional currents... i need to know, because, in the future, i will be designing circuits that depend on there being a "pull". if there isn't for ground, then i guess i'll have to employ negative voltages...
  17. ok so i have questions with electronics that doesn't seem to be covered by tutorials that i've scanned throughout different websites, or i just don't want to read through a lot of material to find that small footnote that i needed to find. i'm basically going to be posting a series of threads named "the finer points of electronics" to have people explain things to me. this may sound like trolling (it's not), but consider this a way to get more activity in these forums. ok so question I: so the tutorials lead us to the idea that common ground is just the charge of the source equal to the
  18. ok this is my solution... though i'm not sure it'll work as i don't know if ground actually "pulls" into it, or is everything a result of positive voltage pushing everything in.... in terms of conventional current... "R_z" limits the current so the "Z" zener diode can produce a voltage reference. the reference is then picked up by the "C1" and "D_av" avalanche diode (whose breakdown is equal to Z) compares it with the actual voltage from source in C2. when the voltage goes below a certain limit, as referenced by "Z", the avalanche diode breaks down and switches the thyristor "Q", which then
  19. so i got this small circuit that plugs to the mains as power source. as for its DC converter, it's one of those transformer-less ones that drops the voltage with a resistors and filters before rectifying and smoothing it. the ones that can only deliver small currents. well, after that, it uses two IN4737 zeners in series to create a reference of 15V. i needed to find how much current is being drawn between the 1) DC converter (as described above) and 2) the zeners and the rest of the main larger circuit. so i disconnected the positive wire between these two and put in series an ammeter. the
  20. or do we have to have wheatstone bridge and more complex ones for the general cases??
  21. ok, i need a simple DC comparator. so would the attached pic do the job?? all resistors are equal EDIT from above ^: my mistake, R1 and R2 (not labelled below) are the only ones that have to be equal. R3 (not labelled below) ideally has high impedance.
  22. i thought i had a solution, but it wasn't doing the right voltage comparison... good thing there's a "remove post" option here in this forum.
  23. i need a component or circuit that cuts off current when voltage drops from a certain level... or basically an SCR (which are usually designed to have a low holding voltage) that instead has a high holding current/voltage (cuts off earlier).
  24. a simple question... so i have to create 8A DC for a very simple section of a circuit for 2-3 seconds. it draws it's power from the 120 VAC mains. i will rectify the AC and condition it witha capacitor, but i cannot use a voltage regulator and/or a transformer before or after the rectification (don't ask). so, i'll simply use a resistor to drop the voltage by 72V. the remaining, to the load, so the whole current is 8A. also, the load needs no regulation. the question is, can this resistor: (http://www.digikey.ca/product-detail/en/PF2472-8R2F1/PF2472-8R2F1-ND/2448327) handle nearly 600W, whe
  • Create New...