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  1. (*steve*)

    One of my colleagues...

    The "Low power load box". This is fairly typical of the construction and documentation style. Ross built a number of battery chargers and dischargers; I assume this came in handy while building these. The base this is built on is steel. It gives it a bit of heft so it sits where you...
  2. (*steve*)

    One of my colleagues...

    You may have noted I have occasionally referred to "one of my colleagues" in some of my posts. Unfortunately the person I most often referred to was suffering from some fairly nasty medical conditions which finally resulted in his death. I was charged by him (and later his family) to ensure...
  3. (*steve*)

    Question on reversing polarity for DC Motors

    OK, here is a simple limit switch circuit: The diodes are arranged so they permit the motor to operate in the OPPOSITE direction once the limit switch opens the connection to the motor. They must be able to withstand the stall current of the motor (at least briefly) as the motor starts...
  4. (*steve*)

    Create controlled 50v pulse

    N channel mosfet. And that driver is inverting, so without an input the mosfet will be ON. What mosfet are you using, and are you testing in reality or using simulation software? And are your grounds (-ve's) common (for 5, 12, and 50V power supply)?
  5. (*steve*)

    Piezo speaker amplifier?

    No, you would have to know the specifications of the original. And those would be difficult to even guess.
  6. (*steve*)

    Datasheets moving about... Grrrr

    I was just looking for the old National Semiconductor AN-140. This was once found all over the place -- so much so that I had neglected to download and save a copy. Over time it had moved to the Fairchild site, and although that was subsumed into OnSemi the old links worked. No Longer... And...
  7. (*steve*)

    Create controlled 50v pulse

    Neither. Turn the PWM on and off from the microcontroller. Have a quick look at the resource on driving LEDs. LEDs should not be driven from voltage sources. Since you're driving it from a power supply, I recommend you set your current limit to a safe value for the LED. Note that if your...
  8. (*steve*)

    Create controlled 50v pulse

    Not for a gate driver (it probably only needs to be powered from 12V). But, in any case, the 2N3904 can't switch anything like the current you need. If you place a diode from base to collector (preferably a schottky diode) you'll see a marked increase in speed. The mosfet will switch much...
  9. (*steve*)

    Create controlled 50v pulse

    If you check the datasheet you'll notice an internal resistor to speed up the switching off of the device. (That's a good thing)
  10. (*steve*)

    Is MW LRS 100-24 a good power supply? + possible leakage solution question

    Ok, after the briefest research... I see a long discussion on eevblog and what appears to be the answer. Earth the power supply Earth the iron Apparently many cheap switchmode power supplies aren't earthed. Correctly earthing them reduces the voltage a lot, and then earthing the tip itself...
  11. (*steve*)

    Is MW LRS 100-24 a good power supply? + possible leakage solution question

    Yeah, that seems reasonable. Let's go back to what you said earlier... Grounding the tip is fine, but it doesn't actually need to be grounded. It just has to be at the same potential as what you're working on. You could use one rail of your low voltage power supply, as long as your work...
  12. (*steve*)

    Create controlled 50v pulse

    A simple Darlington transistor can be slow to turn off. It may be better to use a pair of transistors with the second one having a resistor from base to emitter to turn it off faster. You may find that the voltage drop across the transistor is higher than for a mosfet too. In your case it...
  13. (*steve*)

    cap tester repair

    Oh, I didn't expect that. Did you find a solution for it?
  14. (*steve*)

    Create controlled 50v pulse

    In that post I recommend 2N3904, but almost any other NPN transistor could be used. If you have 2N2222's, or BC548, etc... This circuit will probably deliver a couple of hundred mA to the gate of the mosfet, and that's plenty for most uses.
  15. (*steve*)

    Create controlled 50v pulse

    There are a few things to note about that mosfet. Firstly, it has a gate capacitance of several nF for a certain set of conditions, that may be less onerous than the ones you'll face. Secondly, it is a logic level device which means that it may be slower to turn off if the gate is just pulled...
  16. (*steve*)

    Is MW LRS 100-24 a good power supply? + possible leakage solution question

    But what happened to the voltage at the negative rail? And what do you get when you read the output voltage of the power supply on an AC range? Some cheaper meters (and some not so cheap meters) don't ignore the DC component of a measured voltage on the AC ranges.
  17. (*steve*)

    Is MW LRS 100-24 a good power supply? + possible leakage solution question

    Yeah, give the 200k a go.
  18. (*steve*)

    Create controlled 50v pulse

    If you're using an n channel mosfet as a low side switch them the gate probably only needs to be switched to +10V. Depending on the mosfet, the gate may be destroyed if it's pulled higher than 20V with respect to the source. The circuit I linked to above should be powered by maybe 10V to 15V...
  19. (*steve*)

    Create controlled 50v pulse

    I believe there is a simple gate driver circuit in the resources section. Give me a moment to find it... Hmmmm.... Not in the resources (I should fix that). Look here.
  20. (*steve*)

    Is MW LRS 100-24 a good power supply? + possible leakage solution question

    I think you'll find that very little current can follow via this path. Connect a 10k resistor between the negative output and ground, then measure the voltage across it. I wasn't aware that these soldering iron had an Earth connection. Is there too electrically connected to the negative...
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