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Thread: Op-amp as buffer question

  1. #1
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    Default Op-amp as buffer question

    I may have to build a couple of buffers for my mod lines in an emergency this weekend. Ideally I'd use the LM324 but my local shop doesn't stock them. Would the lm3900 be an alternative I could use?
    It does really need to be able to run from a single supply.

    I've previously built a circuit using the single channel version of the 324, hence my desire to use this one. I'm not really much of an electronics person :-/
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  2. #2
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    LM3900 should work fine. I use MC34071 single supply op amps because that's what I have. Don't forget to tie the inputs to ground on the unused channels.

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    Tl081/082/084 is the best choice TL07* is good enough for me
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    Thanks Dave.

    Did you ever have any issues when you were using Guido's board? When i add it inline between my breakout board and laser modules (a Laserwave OEM-V-SS DPSS head and red and blue driven by your drivers) I get low power.

    I had to build an op-amp buffer on an older LW head, but I've never had (noticed?) an issue with FLexmod driven diodes.

    Unfortunately I only have tomorrow to get these built, so I'm limited in what i can pick up locally.

    LM3900N seems to be the only quad that Maplin do thats single supply.
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    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  5. #5
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    Hey man,

    In the lasers that still use Guidos board, I have a differential amp ( like the pangolin recommended amp ), followed by guidos board, followed by the drivers. No issues.
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  6. #6
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    Quote Originally Posted by norty303 View Post
    LM3900N seems to be the only quad that Maplin do thats single supply.
    Dont use a single supply opamp.

    Use this circuit here: http://www.laserist.org/laserist2008...onnections.htm ( fig 5 )

    Use a TL072 or TL082, but you will need a positive and a negative supply..
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    Im using LT1013 for dual and LT1014 for quad op amps.
    These are precision devices with upgraded performances of LM358-dual / LM324-quad op amps.
    Or LMC6643/6644 for the maximum performance.
    They are run with single rail power supply as well.
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  8. #8
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    Thanks all. Can i use the scanner supply for the pos/neg source?

    I won't be able to get any of the op-amps locally today so this is going to have to be a project for another time now. Priority is finishing the projectors today!
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    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  9. #9
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    Norty,

    The scanner +/- 24 is seven to ten volts too high for most opaps. LM7815 and LM7915 are low cost Voltage regulators (1.75$) that will solve your problem by creating +/- 15V/ I normally do not suggest running signal processing off the scanner supply, but for the low currents you need, the LM series regulators will supply some isolation. They need a small capacitor pair on their outputs (0.1 uf ceramic, 220 uF 24 or 48V electrolytic).

    LM3900 is a Norton Current differencing chip, is referred to as a Op-amp by mistake. It uses a different circuit layout, is not for beginners and has poor stability and bandwidth. It has its uses in automotive and scientific applications, but is not ideal by any means for laser show. LM324 is a horrible, outdated, bipolar device with huge distortion. Go for the TL084 family.

    If your buffering color signals, let me know and I'll draw out the "Clamp" circuit that will protect the flexmods against reverse polarity. If there is any chance that the opamp will be miswired or the inputs left floating, you will need the overvoltage and reverse polarity clamps.



    Steve
    Last edited by mixedgas; 07-05-2014 at 07:14.
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    Steve, I would love it if you could draw up a circuit, but be warned, you may need to treat me with kid gloves on this one.. I can solder stuff to ferro board but what it does is often beyond me

    I have a load of TIP127, TIP122 and L7812CV here that i had for other stuff, will any of those be of use?
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    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

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