Dimmable LED Driver to Modulate Resistive Load

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- Jim Thompson
  
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posted
10 years ago

Mon, Jun 10, 2013 12:40 AM

We can't "understand" an undefined device. Please state the object of you experiments in terms of current, frequency, inductance of the solenoid and its self-resonance, maximum peak current, frequency and amplitude. Then we can help. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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I love to cook with wine.     Sometimes I even put it in the food.

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- Michael A. Terrell
  
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posted
10 years ago

Mon, Jun 10, 2013 3:45 AM

My line was from the early days of radio. :)

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- josephkk
  
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posted
10 years ago

Mon, Jun 10, 2013 7:39 AM

Just the same, it is NOT resistive! Are you unwilling to address this?

Actually, it seems to me that you are ignoring this aspect. You have failed to answer all my previous questions.

If that had a simple answer you would have received it already.

Several here have the knowledge you seek, give us a better chance at helping you by providing adequate information. See the questions i already asked.

I presume at this point that you are driving a Helmholz coil, still rather inductive. Now play fair, how much temporal variation (ripple) in the field due to PWM can you tolerate? How much do you intend to modulate the field?

Get the point?

done

- G
- George Herold
  
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posted
10 years ago

Mon, Jun 10, 2013 5:41 PM

Well buy one and try maybe. I assume you can float the coil. Since it sounds like you are only going to be making a few of these, how about a power opamp configured as a voltage to current converter? Or if it can run with a single polarity, I like an opamp driving a power transistor (npn) coil on the collector and current sensing resistor to ground on the emitter.

How fast a B field change do you need...(over what volume) The brute force way to make it faster is to add some series resistance to the coil, and drive it with more voltage... reducing the L/R time.

George H.