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Ampli suiveur fort courant

Bonjour,

Je recherche une référence d'ampli opérationnel, pour montage en suiveur (ou directement en suiveur dans son boîtier comme l'était par exemple le BUF04), pour transmettre une tension d'entrée +-10V vers la sortie +-10V, avec un courant jusqu'à 200mA.

Il me faudrait un modèle de précision, faible bruit, mais courant.

Les autres critères sont peu importants : alimentation unipolaire ou bipolaire, boîtier CMS ou DIL...

Merci.

Pascal Taunay

  • Hi Pascal,

    I translated your question into English with the aid of Google translate. As i understand it, you are looking for a precision, low noise and high current amplifier which is capable of operating at single or dual supply mode.Am I right?

    For further clarification, can you answer the following:

    1. Where does your input coming from? what is your input range?

    2. What will be the bandwidth?

    3. What is the expected output?

    4. Are you going to implement Voltage to Current (transmitter) or Buffer Amplifier?

    Regards,

    Jino

  • Hi Jino,

    Thank you for your support.

    What I need to do is to deliver a voltage signal that can be 0 to 7V with a current up to 200mA.

    The original voltage signal comes from a PCI board (programmable) but that can deliver a current

    only up to 5mA. So I need a precision buffer (or operational amplifier wired as a voltage follower).

    The signal is DC, or with low variation, so the bandwith is low.

    I have found some components on Internet : buffers LMH6321 or BUF634, and also the LT1206.

    Do you think they can match ?

    Is it better to use a buffer or an operational amplifier wired as a voltage follower, regarding the

    stability (open loop or close loop) and the low noise ?

    I need something accurate to keep the precision of the programmed voltage signal.

    Best Regards.

  • Hi Pascual,

    ADA4870 will be a very good amplifier for your application. It is unity-gain stable, high speed current feedback amplifier capable of delivering 1 A of output current. If ADA4870 is out of your supply range you may also refer to this selection table for other amplifiers with high output current capability.

    Regarding the stability between open-loop and closed-loop; either solution can be made stable but generally a closed-loop amplifier such as an op-amp voltage follower will have much higher precision than open-loop.

    If the amplifier output current is not enough for your application you can try boosting it, just refer to this article AN-968 that discuss on how to get high output current. Also, you can refer to this datasheet (page 24) that deals on using external transistors to boost the output current of an op amp. In addition to this, if you are sourcing the current (whether it's an op amp output stage or a discrete transistors) it will have to dissipate power. Good thermal design will be important, please see MT-093.

    I hope this helps.

    Regards,

    Jino

  • Hi Pascual,

    I am very much happy to help you. Can we close this thread?

    Thanks and Best Regards.

    Jino

  • Hi Pascal,

    1. Rail-to-Rail (input and output) means that your amplifier can accept inputs and generate output voltages very close to power supply voltages. For example, AD8656 (Rail-to-Rail input and output) with a supply voltage of 5V can accept inputs from 0 to 5 V and outputs a typical value of 4.991 V (few mV away from supply voltage).So if you have a single supply application and you want to use every bit of supply voltage it is good to use Rail-to-Rail amplifier.

    2. Voltage feedback op amp responds to an error voltage between the inputs, while Current feedback op amp responds to Current error on the input. In terms of input impedance, both the inputs of the voltage feedback are high while on current feedback the non-inverting input is high but the inverting input is low. Another major difference between them is the GBP (Gain Bandwidth Product). For Voltage Feedback it is constant. For example, if an op amp has a BW of 200 MHz at gain of 1, the GBP is 200 MHz. So for the same op amp at gain of 2 will have a bandwidth of 100 MHz. Current Feedback Amplifiers don't have constant Gain Bandwidth Product. They are able to maintain a wide bandwidth at a higher gain, it is set by the feedback resistors which is provided in the datasheet of Current Feedback Amplifiers.

    I hope this helps.

    Regards.

  • Hi,

    You're Welcome Pascal. Can you mark any of the answers so that we can close this thread? Thanks.

    Best Regards.

    Jino

  • Thank you very much Jino.
    Best Regards.
    Pascal.
  • Hi Jino,

    Last questions before to close, regarding the selection table = what mean and to what

    they apply :

    - Rail-to-rail (In and out) ?

    - Feedback-Type (current and voltage) ?

    Best Regards.

    Pascal.