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lm339 as amplifier

Kamal Najmi
Expert 3295 points
Other Parts Discussed in Thread: LM339

hi

i want to use this device (LM339) as an op amp, my circuit look out as below,

 

 

 please let me know your email so that i can send you the sch.

When have built this simple circuit to experiment, in the simulation look it well but not on my board.

it start to oscillate

What is the problem here and what can I do to drive LM339 as opamp, I needed as an op amp.

 regrads

kamal

  • 0
    TI__Guru* 93105 points
    Hi Kamal.

    The LM339 is a compartor, not an operational amplifier. It is not designed to operate as a closed-loop amplifier like the operational amplifier. If you put feedback around it, it will likely oscillate because it is not frequency compensated.

    Its output is intended to be at one supply rail, or the other. Where as the output of the operational amplifier operates within the entire linear range between the supply rails. Additionally, the LM339 output stage is an open-collector transistor intended to be used with a pull-down resistor connected to the positive supply rail. It only sinks current. Operational amplifiers usually have a push-pull output stage and can sink, or source, output current.

    There are many operational amplifier product available. Here is information about TI's operational amplifier products:

    http://www.ti.com/lsds/ti/amplifiers-linear/operational-amplifier-op-amp-products.page

    Regards, Thomas

    PA - Linear Applications Engineering