pulse dc voltage

Discussion in 'The Projects Forum' started by pafrazier, May 14, 2012.

  1. pafrazier

    Thread Starter Active Member

    Jun 4, 2011
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    0
    Hi,

    What would be the best way to pulse dc voltage on and off from a battery across wound copper coil? Would that resonate the coil at it's resonate frequency?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    No one can answer without a lot more information, such as the inductance, impedance and resistance of your coil, and any other circuit components. A pure inductor doesn't have a resonant frequency. Of course real devices have capacitance.
     
  3. pafrazier

    Thread Starter Active Member

    Jun 4, 2011
    57
    0
    Hi,

    The inductance is 207.306 uh

    self capacitance is 5.901 pf

    resistance is .197 ohms

    dia 4.5 inches

    16 gauge mag wire.

    impedance .2 ohms, Not sure if this is correct. I used online calculator.

    The circuit is basically this coil hooked up to a battery. Adjusting the current with a resistor. Battery is 1.2 volts.

    Is it possible to pulse dc voltage across this coil?

    Thanks
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Yes, you just need to compute the frequency and current, and then choose an oscillator design and parts that can meet those specs. Do you care about the waveform (eg. sine vs square)?

    You should elaborate on what you you're hoping to do. Radio? Inductive heating? Experts here can and will help a lot more if they know what the goal is.
     
  5. pafrazier

    Thread Starter Active Member

    Jun 4, 2011
    57
    0
    Hi,

    I am experimenting with resonant circuits. I am not sure yet on frequency or current. Can you expand more on the oscillating design. Do you have any examples of what those circuits look like? Any websites?

    Thanks
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
  7. wayneh

    Expert

    Sep 9, 2010
    12,123
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    For frequencies below about 1MHz, many an experimenter would use the 555 timer IC. You can find lots of information on it on this website. Crystal oscillators are also handy because they are so simple; power in, accurate clock out. Done. And you can get much higher frequencies than a 555 or an op-amp. But both the 555 and a clock will generate square waves.
     
  8. pafrazier

    Thread Starter Active Member

    Jun 4, 2011
    57
    0
    Thanks for the link.
     
  9. pafrazier

    Thread Starter Active Member

    Jun 4, 2011
    57
    0
    Hi,

    Do you have a simple circuit diagram using a crystal oscillator?

    1.5 mhz frequency pulse, square wave

    1.2 volt battery

    .012 amps

    Thanks
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    I don't know if there are oscillators available that will work at that low a voltage. They're used to generate logic clock signals, and those are usually higher output. The other specs should be no problem - just go shopping.

    You might enjoy this project, wherein I used a 1 MHz crystal oscillator as a radio transmitter.
     
  11. pafrazier

    Thread Starter Active Member

    Jun 4, 2011
    57
    0
    thanks for the link
     
  12. pafrazier

    Thread Starter Active Member

    Jun 4, 2011
    57
    0
    Hi,

    Please see attached circuit. I would like the switch to turn on and off @ 20 khz or faster. What would the switch look like?

    Thanks
     
  13. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Is that 1.2v battery your only power source? If you can use a higher voltage to control it, a MOSFET would make a fine switch. The higher voltage wouldn't have to run anything except the MOSFET, and the 555 timer to set the frequency.
     
  14. pafrazier

    Thread Starter Active Member

    Jun 4, 2011
    57
    0
    Hi,

    I can use the minimum voltage to run the components. What would I need fo supply? What wouild the circuit look like?

    Thanks
     
  15. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Drawing something isn't handy right now, but look up 555 timer circuits, in particular a square-wave generator such as described here. (You can use an op-amp or a comparator IC for the same purpose.) That will give you a way to make a variable (potentiometer-controlled) frequency clock.

    The output can then be applied to the gate of an n-channel, logic level MOSFET which will act as a switch; conducting when "on" and not conducting when "off". Logic level because you want low voltage; a "normal" MOSFET needs 10V to switch on. It would be best if you can put your MOSFET switch between the battery "-" pole and the inductor, instead of between the inductor and resistor, with its "source" pin connected to ground and the inductor connected to the "drain" pin.

    On a positive clock pulse, the MOSFET will conduct from drain to source for as long as the pulse remains positive (gate versus source pins). A low gate voltage (no or low voltage of gate relative to source) will turn off the MOSFET and it will not conduct.

    You'll need about 4V minimum to make this all work.
     
  16. pafrazier

    Thread Starter Active Member

    Jun 4, 2011
    57
    0
    Thanks Wayneh.

    I'll check it out.
     
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