The pictured electromagnet will be PWM'd at 12V / ~100-500Hz.
The goal of PWM-ing the electromagnet is to vibrate a metal bar in close proximity, whose fundamental frequency is the same as the PWM frequency.
This all looks OK in the simulator, but based on other questions and my limited knowledge it
- Might not be possible due to the inductive load of the electromagnet
- Might require a flyback diode
- Might benefit from an H-bridge to reverse the electromagnet's polarity and double the amount that it "pushes" on the metal bar. (Edit: In this case I'd attach a permanent magnet to the bar as well, so that reversing the electromagnet pushes instead of pulls. Forgot to mention this initially)
The primary question is: How do I tell if this PWM'ing strategy will work? Hook it up and see if it gets hot? Can I measure the inductance in advance to figure it out via math™?
(I can split this up if mods prefer, but the basic level of what I'm asking makes me think that it might be best as-is.)
Best Answer
If you want to make the field change quickly and if the inductance is relatively large, the only way to make that happen is with a lot of volts. It sure ain't 1uH. It could easily be ~1H.
You can experimentally try it (with a flyback diode and a low duty cycle pulse) to see how rapidly the current builds up (on an oscilloscope). If it is too slow, you might have to do something like use a higher voltage supply with a resistor (dumping copious heat) in series. If you're just doing a test that might be fine. The field strength is proportional to the current through the coil. Similarly, tying the flyback diode to a high voltage supply will allow the field to collapse relatively fast.
I'm not sure what you are trying to accomplish with an H-bridge unless you are planning to put a permanent magnet on the bar. For a ferroelectric bar the electromagnet "sucks" with either polarity of current.