# Driving a coil Voltage drive? Current drive?

1. May 4, 2007

### kent

Driving a coil....Voltage drive..? Current drive..?

Hi Guys

As the title...I am now having a 10 turns coil, does it really matter that I drive it with sinusoidal voltage signal or a sinusoidal current signal? Will it affect the response of the coil? (like resonance frequency, Q factor...etc)

I am still doing the mutual inductance experiment..(thanks for u guys' help previously! especially Berkeman and Waht)...I am now having a identical coil as the transmitter to be a magnetic induction detector (properly shielded..) what I observed is that the Q factor of my detecing coil is extremely high~! the magnitude of the detected signal at resonance is like 30 times more than the other frequencies....is that a normal observation?

And also, I am now thinking using a PCB coil instead of hand made coil (to make sure all the coils are identical...)Does anyone has this kind of experience? (like the shielding of the PCB...etc)

Thanks you so much for you guys' time!
Kent

2. May 4, 2007

### waht

If you drive a coil with a voltage source, it needs to be in series with a load resistor (if there is one). And likewise, with a current source the coil or anything else for that matter should be in parallel with the load resistor (if there is one).

Resonance is a weird thing, under right conditions when driving an LC circuit with a voltage source in series, you can have large voltages developing, even a 1000 times higher then what you put it, if the Q is really high, but the current would be 1000 times less, and likewise, if you drive an LC circuit with a current source in parallel, large currents will develop, so much so that can even melt your coils when Q is high enough, but voltage will drop of course. That's why sometimes it's good to broaden the Q by inserting a load resistor to absorb some current.

You said your coil has ten turns, so it might have a like 500uH or something, it might be difficult to duplicate the coil on a PCB, and even if you do it will have a different Q, and coupling constants.

And for PCB shielding, anything conductive and grounded placed over the PCB will shield the circuit from the outside world. Nothing significant will get in or out.

Hope that helps.

3. May 4, 2007

### kent

Thanks you!...The size of my coil is quite small...so the inductance of my coil is around 10uH...which is OK...I think...

4. May 4, 2007

### waht

I meant 500 nH not uH sorry. That's what you would typically get with a small 10 turn coil. Coils etches on pcb's are in nH range.