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  1. KrisBlueNZ

    Potential divider problem

    Sure. Pretend R2 (200) isn't there. R1 (100) and R3 (300) form a voltage divider that's connected between +10V (on the R1 side) and 0V (on the R3 side). From there, you can use the voltage divider formula, or you can just notice the ratio of the two resistances, which is 1:3. That means that 1/4...
  2. KrisBlueNZ

    Buck Converter Calculations - Halp!

    His schematic shows a switching converter and he hasn't mentioned a linear regulator. As you say, a linear regulator is always an option but it wastes power. He could use a switching pre-regulator and a linear regulator for the last few volts, but at 5A he would still be wasting and dissipating...
  3. KrisBlueNZ

    Potential divider problem

    Ah, so this method works where voltage sources are fully isolated from each other. That's an advantage over the Thevenin equivalent method, which assumes all voltage sources are galvanically connected. That's usually the case but not always. Yes I noticed that. It is similar to the Thevenin...
  4. KrisBlueNZ

    Buck Converter Calculations - Halp!

    Do you mean that the supply you're feeding into your charger circuit has a 5A current limit? If so, that's not a workable way to do things. If your circuit pulls too much current, the power supply will limit by dropping the output voltage, and your circuit will no longer work properly. You need...
  5. KrisBlueNZ

    Potential divider problem

    Thanks Steve. I think I understand. If I try to explain it the way I understand it, can you check that I've got it? You turn off all the external voltage sources by replacing them with shorts to 0V, then you turn one on at a time (separately, not cumulatively) and do a separate calculation for...
  6. KrisBlueNZ

    Potential divider problem

    I'd be interested to see that too, Steve.
  7. KrisBlueNZ

    Potential divider problem

    Yes, that's all correct. And the current through R2 is 45.5 mA. The current through R1 feeds INTO the summing node (assuming conventional current) and the R2 and R3 currents feed OUT. So the total current is: 59.1 - 45.5 - 13.6 = 0 mA as a final check. Good work, you understand this stuff well.
  8. KrisBlueNZ

    LED strobe circuit needs more current

    No, the 33 ohm resistor in the Q2 collector circuit. It's marked R3.
  9. KrisBlueNZ

    LED strobe circuit needs more current

    Well, I simulated that original circuit in LTSpice and it doesn't even oscillate! I shorted out the LED, to make it pretty close to a standard two-transistor relaxation oscillator, and now it oscillates. If you really want to stick with that circuit, you can add a buffer to drive the LED...
  10. KrisBlueNZ

    LED strobe circuit needs more current

    Sorry, you did. But I've never heard of a 5V battery. Can you be more specific? How big is it? How much current can it supply? The important factor is what you're intending to use eventually, not what you're testing with. I've made some suggestions on how to get acceptable, easily controllable...
  11. KrisBlueNZ

    LED strobe circuit needs more current

    Can you answer more of my questions? What's your power source?
  12. KrisBlueNZ

    Potential divider problem

    There are probably lots of ways to solve this problem. The way that appeals to me is to use Thevenin equivalents. I'll explain how to do it, without giving you the answer. (This looks like a classic homework problem; if so, you need to know HOW to solve it, not the solution.) Two resistors in...
  13. KrisBlueNZ

    LED strobe circuit needs more current

    Can I back up a bit. What are your design requirements? Your critical requirement is high LED current, right? What is your power source? Is it a power supply or a battery? What voltage, and what output current capability? What type of LED are you using? Do you have a part number for it? What...
  14. KrisBlueNZ

    Buck Converter Calculations - Halp!

    As BobK suggests, you should use a P-channel MOSFET, with drain and source reversed (source connected to the incoming supply positive rail). Alternatively you can use an N-channel MOSFET if you provide a suitable gate drive waveform. As it stands, using an N-channel MOSFET, the design won't...
  15. KrisBlueNZ

    Can opamp provide low voltage output?

    (re higher impedance after the diode) I think you're overestimating the problem. Unless you have a lot of capacitance in the feedback loop, you should be fine. This is why I asked you to post your proposed error amplifier circuit. I doubt there will be a problem.
  16. KrisBlueNZ

    Can opamp provide low voltage output?

    No, because the feedback is taken after the diode, so the voltage after the diode is what is being controlled by the op-amp. Yes, that specification seems pretty clear. It won't be THAT low! I think one diode is enough, but there's no problem using more than one, since the feedback is taken...
  17. KrisBlueNZ

    Who Is This?

    Well yeah... I don't wear a burqua nowadays :-) I'm not sure what you mean... Is it that I'm clean-shaven? Or because I cropped it inside my hair line? Yes, I've seen it before - on LinkedIn maybe, and had to smile. Miguel, perhaps you should ask your partner to take some photos of you, at the...
  18. KrisBlueNZ

    Can opamp provide low voltage output?

    I second CDRIVE's suggestion. If the op-amp's output won't go all the way down to 0V you can just connect a diode in series with it, with its anode to the output pin, and a resistor from its cathode to ground to ensure some current flows in it. In this case, the LD input of the HV9910B just...
  19. KrisBlueNZ

    Who Is This?

    Regarding "Corrector", I've never seen a more obvious case of trolling with a major attitude problem. I consider his posts likely to cause offence and waste our time, and well within the boundaries of unacceptable. If it was my decision, his account would be gone, and his posts would be moved...
  20. KrisBlueNZ

    +/-40V SMPS virtual ground

    The transformer should provide isolation between the primary-side circuitry and the secondary-side circuitry. So you can connect mains earth to the virtual ground rail if you want to. The latter description is right. The virtual ground generator operates from an 80V supply and generates an...
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