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  1. KrisBlueNZ

    Need an automatically cycling test current source

    Also, how accurate do the currents have to be, and how smooth do the changes need to be? In other words, would it be OK for the current to change in steps of, say, 0.1 mA, or does it have to move totally smoothly? And do you have experience with microcontrollers?
  2. KrisBlueNZ

    FET switch circuit - is it correct

    You're right! I went through all the calculations and came up with 60 µA base current, then I read shumifan's calculations and everything looked right, and I must have ignored the final result! I didn't use the Thevenin equivalent method. I calculated the resistor currents separately. The...
  3. KrisBlueNZ

    (90-660) volt into (0-277) volt power supply

  4. KrisBlueNZ

    FET switch circuit - is it correct

    Your calculations for the base current are exactly right. Assuming a current gain of 100, 120 µA base current will allow 12 mA collector current which is plenty. Assuming R6 is 3k3, R6+R7 = 36.3k and at maximum V=12.6V, I = 12.6 / 36300 = 0.35 mA. So Q3 will saturate easily. You could reduce R3...
  5. KrisBlueNZ

    Designing a Time Delayed Relay

    What type of relay are you planning to use there? All of the relay types I recommended on the schematic are laid out differently from that outline...
  6. KrisBlueNZ

    Designing a Time Delayed Relay

    Arcing won't happen because there's no significant voltage between those points. Lots of current will flow through the Allegro chip but the voltage across it will only be millivolts. The clue to this is the fact that pins 1,2 and pins 3,4 are connected together internally by a section of metal...
  7. KrisBlueNZ

    FET switch circuit - is it correct

    That looks pretty good. R3 should be 33k to avoid a lot of wasted current. The DMP2215L's maximum gate-source voltage rating is 12V. I would add a 10V 0.5W zener (1N5240B) with its anode to the gate and its cathode to the source to protect it. Also, R6 could be a lot higher - 3k3 for example...
  8. KrisBlueNZ

    Digital programmable CDI ignition for 2-stroke engines

    This sounds like a pretty advanced project for an electronics noob. Lots of things to get exactly right before the engine will run at all. Can you give us some more information about the project? What components do you have? Have you chosen your coils? What's the battery voltage? Can you give...
  9. KrisBlueNZ

    Help with replacement for a rotary switch

    Cool :-)
  10. KrisBlueNZ

    Circuit Help !!!

  11. KrisBlueNZ

    Replacement for a microcontroller

    If you're interested in building a circuit that generates a signal that can be received by a sound card, there are a number of VCOs available. Here's a link to the Digikey selection guide; many of these devices are probably suitable...
  12. KrisBlueNZ

    Circuit Help !!!

    That circuit is a boost converter. For a fixed load, the input power is roughly constant. This means that the amount of current it draws is inversely proportional to the voltage, because power = voltage * current; less voltage means more current. So when the power supply is initially connected...
  13. KrisBlueNZ

    Circuit Help !!!

    You haven't given enough information for us to even guess at the problem. If you have the schematic, upload it! Do you have a cellphone? Take some pictures. You have the power supplies in front of you, right? They have labels on them don't they? What do they say?
  14. KrisBlueNZ

    Circuit Help !!!

    Give us as much information and photographs as you can. Manufacturers, model numbers, labels, component markings, photos of everything.
  15. KrisBlueNZ

    Circuit Help !!!

    Double-check that you have the polarity right. What are the specifications of the two power supplies? More information and some photos might help.
  16. KrisBlueNZ

    Connectivity of plated through holes on double layer boards

    Plated-through holes are plated through, so you don't need the solder to wick through the hole. It will normally fill most of the hole but it may not come all the way through and coat any of the copper on the other side. For vias, i.e. through-plated holes that aren't intended to have a...
  17. KrisBlueNZ

    Hello all!

    Hi Brandon :-) Thanks for introducing yourself, and welcome to Electronics Point :-)
  18. KrisBlueNZ

    12v fans, simple question

    In the crude analogy I used in post #2, a fan is like a tension spring. When you hook it between two points that are 12V apart, it tries to pull them together. The power supply is regulated, so it keeps them 12V apart, and this creates tension (current flow) in the spring. If the spring is too...
  19. KrisBlueNZ

    Help with diagnosing problem with pcb from charge controller

    Sorry, you're right. There are only four. You've told us the markings on one of them. It's likely that they're all the same, but not certain. Can you check the others please. While you have the heatsinks removed, can you take a few photos of what's underneath them (i.e. between the heatsink(s)...
  20. KrisBlueNZ

    FET switch circuit - is it correct

    Those circuit references relate to the schematic in post #20. RDS(on) of 4~5 ohms should be fine for that circuit position. Total steady-state current should be less than 20 mA.
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