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Can we buffer 12v power by using a 12v rail-to-rail op amp?

Other Parts Discussed in Thread: OPA743, OPA4243

Hi, I'm new to power management and am currently designing circuits to manage 12v power input from adapter. The voltage coming out of wall is around 12v and I want to use OPA743 to buffer it. Can I use this 12v power input to both power up OPA743 and to use as signal input so that I can get a 12v at output? If not, is there any buffer amplifier you suggest me to use instead? Thank you!

  • Hi Chenxin,

    No. Operational amplifiers may have input, and will have output range limitations that prevent them from being able to produce an output level equal to the supply rail levels. The OPA743 has a common-mode input range that exceeds the positive supply rail by +0.1 V; however, the output can only swing to within about 75 mV of a supply rail with a 100 k-ohm load, and 450 mV with a 1 k-ohm load. Any linear IC component, even a low-dropout regulator (LDO), will have some limitation on how close the output voltage will be in relation to the input voltage.

    If a boost-type regulator, or charge pump IC, is added to the circuit such that the op-amp's V+ line could be raised above the input voltage level, say +15 V to +18 V, then the op-amp could be powered from this higher level while buffering a +12 V input. The OPA743 has a maximum V+ rating of +13.2 V and you really wouldn't want to power it at that level. Another rail-to-rail input/output (RIRO) op-amp would be a better choice. Do note that every op-amp does have a maximum output current  capability. One would have to be selected that has sufficient output current for the application.

    Regards, Thomas

    PA - Linear Applications Engineering

  • Thank you Thomas,

    So I'm considering changing to OPA243. If I don't want to do adjusting, do I just leave offset trim pins(pin1 and pin5) disconected? Thank you!

  • Hello Chenxin,

    I do find an OPA4243 listing which is for a quad operational amplifier, but I don't find one for an OPA243. Regardless, if you find an operational amplifier that you want to use and it has offset control pins, most often those pins can be left floating if the function isn't needed. Be sure to consult the amplifier's data sheet. It is usually quite clear about utilizing, or not utilizing, the pins and what to do with them in either case.

    Regards, Thomas

    PA - Linear Applications Engineering