Re: Coils

On Sat, 11 Aug 2007 16:31:54 -0700, KBSoftware <kbsoftware@xxxxxxxxx>
wrote:

I a bit new to electronics, about 1.

Now I'm learning about coils, and have a few questions.

I have some coils and I know their Henry rating, I've found a lot of
information on coils.
Now I'm wondering if I took a coil let's say a 55uH applied maybe 3v,
what would be the voltage resulting. I've seen a coil used in a 3v to
9v dc-dc converter and that's why I'm wondering. I think the coil
increases the 3v to some other voltage (the circuit used a 47uH), then
an ic was used to regulate the output from the coil to 9v about.
Is there a formula that could help me here.

Or could I just build that simple circuit and using a multimeter
safely read the voltage and amps that is being produced. What I'm
worried that the voltage being produced is high and might damage my
multimeter.

You have a coil and have a source of DC voltage through the coil - you
interrupt the flow and the collapsing magnetic field attempts to keep
the current flowing - no matter how much voltage that may take.

In theory.

In practice, the speed of change in magnetic field determines how high
a voltage you can achieve. Just like a generator - faster the field
changes the higher the voltage. The coil form - wire thickness - and
other construction influences determine field collapse time.

I use a 3 millihenry choke in a 2 volt DC NPN collector circuit
switching at 10 KHZ and get 80+ volts out, and if I don't tame it, it
eats the 30 volt transistor doing the switching.

You won't damage the multimeter. You may get a reading that makes no
sense - that's HF noise impressed on the signal you want to read. Use
an old fashioned moving coil meter if you have doubts or filter the
voltage to the multimeter (not always easy - high impedance meters
pick up noise from the environment - that's the nature of things).

Show us the circuit ?

I use mine to get 10 volts from a 2.5 volt source so I can switch a
mosfet that requires 8+ volts.
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