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sin wave generator

or sam
Expert 2020 points
Other Parts Discussed in Thread: LMV611, OPA544, LM675, LM386

Hi

I am trying to use lmv611 in order to generate wave generator.

I am building simple wein bridge (see below) where: r1=r2=160k, c1=c2=100n rf=20k rb=10k (f=~10hz).

1. without a load I get to cut sin wave - the max amplitude is cut at 4V because when I set my power source to -5-5 the current raise and the amplifier stops working - it is strange    for me because it suppose to work until 5V . so how come the amplifier cant work in -5-5V?

2. when I connect the load same phenomena happens juts now it is cut at 0.6V. Is it because the currents are to high (150mA)?  

R-load=~8ohm 

Does the reason is the high currents?

 which amp  is better for me in order to achieve 250mA currents on that load?

thanks in advanced,

.

  • 0
    TI__Mastermind 49966 points

    Hi Sam,

    The LMV611 will NOT work in this application. Your supply voltage is too high and the load is too much.

    I will assume "-5 - 5" means -5 and +5V supplies, which is 10V total, which is higher than the 611's maximum of 5.5V.You need a device with a supply max of 10V or greater.

    The LMV611 can linearly drive about a 20mA current....minor problem there.

    You need a amp that deliver much higher current, with higher voltage.

    There are some op-amps that  can deliver >200mA, but some of them are high speed and can be difficult if they are not laid out carefully using high speed layout techniques..

    Since your load is 8 ohms, what you really want is an audio power amplifier.

    I would recommend you look at the OPA544 and LM675 power op-amps.These are designed to drive >1A current. Be sure to add a heatsink, too.

    The LM386 audio amplifier has a Wien bridge oscillator circuit in the apps section. For 10Hz, you would need to increase the size of the 50uF output cap (~200uF or larger). The advantage is it can be used on a single supply without any external biasing.

    If the Wien bridge is "clipping" you need to reduce the value of Rf until it stops clipping. The overall gain is set by the ratio of Rf over the resistance of the lamp.

    Have a look here about the lamp : http://www.moorepage.net/Lamps.html

    Regards,

  • 0 in reply to Paul Grohe
    Expert 2020 points

    Hi

    thank you very much for the fast and detailed answer.

    I will try it with the amplifiers you recommended on.

    thanks,

     

  • 0 in reply to or sam
    Expert 2020 points

    Hi

    I have looked at those datasheets and it seem that they are very big and it seen to be overqualified amps.

    I need this amp to be used in very small device that can not be heated.

    I have tried to find some other amps but could find anything with current bigger than 100mA

    if I can you recommend on qfn or other small package that can carry around 150mA on load that is between 5-20 ohm?

    thanks.