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  1. (*steve*)

    simple current limiting to 2A with TIP122

    http://jeelabs.org/2012/11/24/its-a-current-source/
  2. (*steve*)

    simple current limiting to 2A with TIP122

    You really can't explain what you're doing. You say you need a 2A current limit, yet all the explanation I've been able to get out of you suggests that 1/8th of that current is sufficient (which, by the way, goes a long way to explain why someone would attempt it without a heatsink). It seems...
  3. (*steve*)

    simple current limiting to 2A with TIP122

    I can't see where you get 2A from. 7 segments times 30mA is 210mA. A limit of 250mA would be fine. Or just use a 500mA fuse.
  4. (*steve*)

    how tolerant is USB?

    I did some tests today. I hooked up a device via USB and shouted insults about the USB standard to it. It proved to be very tolerant of that form of abuse.
  5. (*steve*)

    Ultra Bright LED Dimmer with a sliding potentiometer

    The resistance is too high to use directly. One option is to create a variable duty cycle 555 oscillator using the pot to control the duty cycle and drive the led his a resistor from the 555's output.
  6. (*steve*)

    Which chip used to optimize measuring many batteries.ject

    If you have ten 12V batteries in series you would need a 150V mux and you would require a common ground with the battery pack. But you'd have problems with that. You could use dc optoisolated mosfets (dc ssr) but you would also need a large number of these and they would need to be rated for...
  7. (*steve*)

    Heatsink for KA7805?

    If you can run it with a lower input voltage the regulator won't get as hot.
  8. (*steve*)

    Can someone explain me how a BJT works?

    There are several mathematical models of the BJT (for example). Each differs in the degree to which it models the transistor. Do you want to dive straight in to a stack of formulae which model stuff you don't know about yet or start with simpler approximations (which may be fine for many...
  9. (*steve*)

    simple current limiting to 2A with TIP122

    I don't understand. Are you driving 8 x 8 digit 7 segment displays? Is the TIP122 the driver for the segments or for the digits? Remember that in a multiplexed display only a single digit is on at any time. The digits are scanned through quickly to give the illusion that all are on.
  10. (*steve*)

    simple current limiting to 2A with TIP122

    What is the TIP122 doing? In a multiplexed display it will either be driving a max of 30mA or 240mA depending if it is a row or column driver. In either case it shouldn't be shorted out and if it is, you've done something badly wrong. Is it a LED display? If so, why the 24V supply?
  11. (*steve*)

    Multiple Sliding Doors - Hobby

    The now deleted suggestion to use a serial servo controller is not bad considering the challenges involved in driving multiple servos at once.
  12. (*steve*)

    Heatsink for KA7805?

    @Two Volt, your answer ignores the voltage differential. Try it with a 20V differential :-D
  13. (*steve*)

    simple current limiting to 2A with TIP122

    I can guarantee that is the number of watts if your TIP122 is driving 2A into a short from a supply at 24V. The heat sink will likely be about half the size of your fist. If this is really what you want, I can point you to a circuit (in fact, you may be able to find one similar in the LED...
  14. (*steve*)

    simple current limiting to 2A with TIP122

    @azadfalah, you really seem to be enjoying this thread :D
  15. (*steve*)

    Which chip used to optimize measuring many batteries.ject

    Or are the batteries even connected in any way? If they are, do they share a common -ve (for example) If the answer to all this is "it can vary" then you may have to use relays to switch birth dudes of the batteries and logic to ensure only a single relay is powered. Additionally you will need...
  16. (*steve*)

    Heatsink for KA7805?

    It all depends on the current and voltage differential. But practically speaking, if it doesn't get hot you're OK to go.
  17. (*steve*)

    simple current limiting to 2A with TIP122

    How large is the heat sink on your TIP122 considering it may dissipate 48W?
  18. (*steve*)

    voltage and current relationship for capacitor?

    The (capacitor) voltage will only change over time if the (power supply) voltage changes over time. With a capacitor across a voltage source the capacitor voltage and the power supply voltage are the same thing.
  19. (*steve*)

    Multiple Sliding Doors - Hobby

    Please only post a single thread. Posting multiple threads as you have done is very bad for your karma. I fear you don't understand servos. You don't need limit switches to tell you if they are open or closed. And you'll have to do some programming at the very least. Is this a school project?
  20. (*steve*)

    Can someone explain me how a BJT works?

    Generally speaking, the load is the thing you are controlling with the transistor. It may be a relay, a light bulb, a LED, a speaker, or a resistor or any of a plethora of different things. A transistor isn't perfect. If it is controlling a large current, especially if it's not just being...
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