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  1. M

    choosing an active probe for Rx NFC measurements

    I looked on a few sites and had the impression that there are two kinds of active probes: 1) those that are designed for lower voltages (say up to 20v or 50v) and cost around 1000USD upwards; 2) those - a bit like this one - that seemed to be designed with measuring higher voltages in mind -...
  2. M

    choosing an active probe for Rx NFC measurements

    Is it OK that this product seems to have two long and separate leads? I'm used to trying to minimise the area of the loop between ground and tip at the end of a conventional passive probe.
  3. M

    choosing an active probe for Rx NFC measurements

    Following NXP guidelines for selecting the right passive components between antenna and Rx pins of PN7462 NFC controller, they recommend using an Active probe with a low capacitance (<2-3pF) for taking voltage measurements at the pins during communication. The cheapest active probe on Digikey...
  4. M

    best practice for orientation of wired linear plugs (JST SH)?

    JST SH (1.0mm pitch) 5 pin plugs can be placed at either end of an array of wires in an UP or a DOWN orientation. (Borrowing from FFC terminology here.) For example, this vendor (see product photos) seems to propose what I'll call UP-UP products...
  5. M

    Chassis cooling of thermal pad on stepper driver ground plane

    Silicone thermal pad. Yes that's it! Thanks a lot, hadn't heard of those and was wondering what could be used. You're right, could find a way to include a bo such that there are screws on both sides of the driver chip. Until now hadn't wanted to lose any (radiating) copper pour to screw holes...
  6. M

    Chassis cooling of thermal pad on stepper driver ground plane

    A stepper driver (TMC5130) is mounted on a 4 layer PCB with thermal vias under the part. The bottom layer is a GND plane. The PCB is mounted on a machined aluminium block that carries various mechanical parts and effectively forms a part of the chassis. I'd like to machine the aluminium block...
  7. M

    Is an opamp better next to the current sense resistor or closer to a microcontroller?

    Re: opamp better next to current sense resistor or near to microcontroller? Noted. (On precision: ultimately the role of this measurement is to provide a programmable fuse, but first will it to monitor circuit performance in real time and learn how to get good performance out of the parts.)...
  8. M

    Is an opamp better next to the current sense resistor or closer to a microcontroller?

    Re: opamp better next to current sense resistor or near to microcontroller? ;) about 100mm but there are potential noise sources on the board - like a 24v boost convertor and a 12v battery charger. The precision doesn't have to be amazing in this application, but wanted to understand "best...
  9. M

    Is an opamp better next to the current sense resistor or closer to a microcontroller?

    opamp better next to current sense resistor or near to microcontroller? Am measuring currents in a 24v line using a CS30 highside opamp and a PIC18F microcontroller running at 5v...
  10. M

    2 * 24v outputs of 2A each: supply with one 12v 4A boost or two 12v 2A boosts?

    Gosh @Klaus, you are right and none of those fuses are suitable. This would be the appropriate range from the same constructor. https://www.littelfuse.com/~/media/electronics/datasheets/resettable_ptcs/littelfuse_ptc_lowrhosmd_datasheet.pdf.pdf Both of the 4A (Ihold) offerings have trip times...
  11. M

    2 * 24v outputs of 2A each: supply with one 12v 4A boost or two 12v 2A boosts?

    OK. Looking at a specific example, 4A trip is indeed necessary to get a sufficiently high Ihold to avoid tripping. https://www.littelfuse.com/~/media/electronics/datasheets/resettable_ptcs/littelfuse_ptc_1210l_datasheet.pdf.pdf The terrible thing is that the 4A with an 8A current would take 1...
  12. M

    2 * 24v outputs of 2A each: supply with one 12v 4A boost or two 12v 2A boosts?

    @Easy peasy a 4A on the 2A output is something I'd never have guessed. Just to try to understand, are any of the following pertinent to your application (or somethings entirely different)? - is it local heating that makes a 2A inappropriate? - are there transients in the load that surpass 2A...
  13. M

    2 * 24v outputs of 2A each: supply with one 12v 4A boost or two 12v 2A boosts?

    OK so in this context the choice of polyfuse is quite important. Presumably, given the temperature derating, it's a good idea to place it as far as possible from the switching area, quite possibly off board? How do we account for the "slowness" of the cutoff? By choosing a value a bit under...
  14. M

    2 * 24v outputs of 2A each: supply with one 12v 4A boost or two 12v 2A boosts?

    @asdf44, good point. The outputs each go to stepper drivers and it's true that when driven by switching supplies, these motors benefit from some apparent overcapacity. Putting them both on a single 4A would mean that one motor might benefit from a little extra torque for acceleration (if the...
  15. M

    2 * 24v outputs of 2A each: supply with one 12v 4A boost or two 12v 2A boosts?

    Supposing you make a box with 12v going in and 2 outputs each offering 2A at 24v. You could use a single 4A boost converter. Or you could use two 2A boost converters, one for each output. It seems that 2A boost converters are MUCH smaller, lighter and CHEAPER than 4A converters. The inductor...
  16. M

    appropriate approach for low voltage device with integrated UPS?

    Hi Klaus, 4A peak 0.5A standby 1-2A typical 30 mins runtime on battery Maximum charging current limited during periods of maximum operational current draw.
  17. M

    appropriate approach for low voltage device with integrated UPS?

    I’m building a device about the size of a piece of furniture that has a 24v line for stepper motors (it could be 20 or 30… but run much better than with 12v), then a number of cards running at 5v for NFC, wifi, TFT display and various sensors. The whole thing is supposed to be “low voltage”...

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