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  1. BobK

    do i need resistor for 50-70 leds?

    That's a good thing,since you would have to change the battery approximately 168 times. In other words, it's going to last about an hour. Bob
  2. BobK

    Would Like A Recommendation

    LTSPICE is pretty good in my opionion and it is free. The only drawback is the lack of a large library, but you can any part you can find a spice model for. Bob
  3. BobK

    convert switching-mode PS to stabilized PS?

    The noise will be in millivolts. So the 15V might go from 14.095 to 15.005. This willl not switch the MOSFET on and off. It would have to swing from 15V down to mayby 3V or less. Bob
  4. BobK

    Hobby builder

    Before, you were using a MOSFET driver, now you want to build one out of discrete components. That sounds like a step backwards to me. Also, I seem to recall having calculated for you that 0.1A per gate would be fine. You only need really high current if you are switching at hundreds of...
  5. BobK

    Flashing 5watt led?

    I have an RGB 3-Watt LED on a star that has up to 2 colors at full brightness continuously on, (i.e. 2 Watts) and it gets hot to touch but not enough to burn you, with no heat sink. I am pretty certain you can get by with no heat sink at a duty cycle of even 50% and it will only be warm. Bob
  6. BobK

    help of a 23A battery to 12v Car battery project

    Nope, the capacitor should go across the + and - terminals at the devide side. Bob
  7. BobK

    PCB Induction Charger

    Okay, I did some calculating for you: It looks to me like your board is abouut 50cm square with the traces being about 1mm spaced about 1mm with 12 turns in the spiral. This caluclates out (thanks Harald) to a whopping 3.5uH. At 50Hz this has an impedance of 0.001 Ohms. At 200KHz (the...
  8. BobK

    PCB Induction Charger

    Well, if you put a 50Hz signal into the inductor you are talking about, it will pretty much look like a short circuit, so I'm not sure what the signal generator will do with that. You should use the highest frequency the generator can produce, then there is a chance it will develop some...
  9. BobK

    Time delay Circuit-How?

    Or you could always do it with a PIC and crystal, no seperate real-time clock needed, just some programming. Bob
  10. BobK

    Really dumb question

    If you give us a link to one of the LEDs you bought, we can tell you how to make it light up. Bob
  11. BobK

    my transistor gets hot, line follower/dark sensor

    And some specs on the motor would not hurt. Bob
  12. BobK

    convert switching-mode PS to stabilized PS?

    Yes, switching supplies might have high frequency noise. But I use them all the time. Are you experiencing a problem that you think is due to power supply noise? Bob
  13. BobK

    Switch on load only when alternator is running?

    Yep, as you can see there is actaully a comparator in the TL431 as well as the reference and a pulldown transistor, so basically it is used here as a comparator with a builtin reference. Bob
  14. BobK

    Switch on load only when alternator is running?

    And you still don't since there is no voltage comparator in the circuit. Kris is using a trick based on the fact that a shunt regulator will draw a current only when the voltage is above the set voltage. A comparator is a bit different and would require a separate reference, which is why this...
  15. BobK

    convert switching-mode PS to stabilized PS?

    What is a stablized power supply? Bob
  16. BobK

    I want to understand everything about transistor and capacitor

    You need to start with a basic electronics textbook and read and understand it. "The Art of Electronics" by Horowitz and Hill is a good one. Bob
  17. BobK

    the right tool

    geeky, So which of these do think Steve's suggestion would not cover?
  18. BobK

    Hobby builder

    AFAIK that driver chip is designed to connect directly to the gates, nothing else should be needed. Bob
  19. BobK

    The control circuit in the engine speed and reverse

    Nah, you just haven't developed my high level of cynicicism. Bob
  20. BobK

    Hobby builder

    You can calculate how long the MOSFET will be in the linear region by dividing the Qg (total gate charge) by the gate current. For your device Qg is 42nC. So at a gate current of 1A it will take 42nsec to charge the gate fully. This is an upper bound on how long the device will be in the...
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