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November 20th, 2017, 11:10 PM   #1
Joined: Nov 2017
From: Shenzhen,China

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Help me implement this electromagnetic mirror curcuit

One of the units in the OpAmp was damaged, so it was malfunctioning when connected to the load.

Currently, I use a function generator and a simple voltage divider to create a required signal to drive a galvo-mirror (no datasheet available, the coil resistance was measured 16-17 Ohms). The circuit below works, but it is oversimplified, and I believe, there should be additional circuitry to stabilize, protect, etc. the circuit.

My simplified circuit

The other problem is that my signal is derived from DAC and comes out as a saw tooth wave ranging 0-5V (see the schematic below). Scaling the output of the DAC to feed into the OpAmp from ADI (datasheet: is not a big deal - I use a trimmer R1 to make the wave range from 0 to 1.6V. The next step is to offset the wave to the same voltage as the other input (in this case +2.5VDC):

What are the additional components that should be introduced to the circuit, excluding bypass capacitors, that would ensure proper/better performance of the circuit.
What would be a good way to offset the voltage between R1 and the OpAmp input without introducing any additional active components (transistors, OpAmps...)
The principal schematic would be appreciated.
It seems trivial to simply provide 0-1.6V wave to input1 and provide 0.8VDC to the second input of the amplifier, and no deed in offsetting the wave. However, it makes the signal to slightly rail out, so I prefer to run the voltages in the midrange at 2.5V.
vivitern is offline  
November 21st, 2017, 02:08 AM   #2
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I don't think

I don't think that anybody know what you are asking?
I think I know what you need.
But Are you try to design your post in mathematical question?
I can help you if you write suppose Assembly Instruction, because of my knowlage in computer. If you write it in Assembly I think I could help.
shaharhada is offline  
November 21st, 2017, 07:32 AM   #3
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I don't think that anybody know what you are asking?

OP amps don't drive directly into mirrors.

Do you mean what we call "current mirrors" in circuit terms, not shiny silver surfaces?
Attached Images
File Type: jpg currmirr1.jpg (25.1 KB, 3 views)

Last edited by studiot; November 21st, 2017 at 07:36 AM.
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November 21st, 2017, 02:14 PM   #4
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Was it you, vivitern, that posted the question here?
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November 23rd, 2017, 12:37 AM   #5
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I think I understand this, and there is a simpler solution. If you take the output from your DAC and use a potential divider to the 2.5V output from the op-amp providing the virtual earth instead of 0v, then buffer that with the 2nd op-amp, you should be able to get a control range of 2.5 +/- 0.8v

Essentially, in your 2nd circuit, just move the ground connection from your Pot and connect it to the 2.5v output from the amp on the right, with 0v out of the DAC set the pot to give you 1.7v, then connect the 2 '??' together, job done.
I assume the maximum current of the Galvo is 50mA?
weirddave is offline  

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