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Topic: DAC output to amp - control magnet coil. (Read 127 times) previous topic - next topic

DocStein99

I would like to take the variable voltage output of DAC MCP4725 0-5v, and amplify that to control this magnet coil.  I'm lost between mosfets, darlington transistors, op amp, variable voltage regulator.  What's the simplest easy device for me to pick to get this task done?

MorganS

Ditch the DAC.

Use a logic-level MOSFET. A PWM output will be much more efficient and easier than an analog amplifier.
GoForSmoke: "What GShield? You never mentioned a shield."

MarkT

By magnet coil you mean an electromagnet?  IE a low-bandwidth is fine, in which case PWM is good.

You should give details of the electromagnet, datasheet, voltage, current, all the stuff we need to know...
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

DocStein99

I have to use a DAC.  The coil measures about 10 ohms, near a strong magnet.  I have no way to pull up the datasheet for a voice coil in a 2.5" IDE hard drive.  The closest thing this can compare to is probably a speaker.

A PWM signal will not work, it just makes the coil vibrate faster, slower or stick in the full-blast position.

The coil responds to voltage to move the angle. 

allanhurst

Use a MOSFET plus a schotty diode flywheel  with a low esr capacitor - that makes it into the output stage of a switchmode buck regulator

regards
Allan

MarkT

I have to use a DAC.  The coil measures about 10 ohms, near a strong magnet.  I have no way to pull up the datasheet for a voice coil in a 2.5" IDE hard drive.  The closest thing this can compare to is probably a speaker.

A PWM signal will not work, it just makes the coil vibrate faster, slower or stick in the full-blast position.

The coil responds to voltage to move the angle. 
The phrase to use is voice-coil - yes, that is like a speaker and you might well do best with an
analog drive if high bandwidth is needed - however you might want to consider ultrasonic PWM
if audible vibration is the problem.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

JohnLincoln

How about using an opamp, with a transistor to buffer the output and supply the required current, as described here.
By including the transistor in the feedback loop you can get unity gain, and so the output voltage will be the same as the DAC output.

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