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  1. #41
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    Re: how to boost microvolts to higher voltages?

    Quote Originally Posted by FvM View Post
    I feel that some points should be sorted out.

    You have been originally asking how to amplify ĩV signal to mV, with minimal supply voltage.
    Later you switched to 1.45 V input voltage and 8V supply. I guess you did so to have a simple problem description. But the solution will be probably different, hence we should agree if we are discussing the first or the latter question. I'm referring to high level amplifier here.

    It has been already stated, that the single supply circuit in post #19 only works with an OP that has a input common mode range including the negative supply rail. NJM4558 isn't of this kind. Even with respective OP common mode range (as exposed e.g. by LM358), the inverting single supply amplifier can't amplify a positive input voltage, as also stated.

    There are several solutions:
    - use dual supply which enables the circuit to amplify signals of positive and negative polarity
    - use an OP with input common mode range down to and including the negative supply rail

    To amplify a positive input voltage > 1V, NJM4558 can be even used in a non-inverting single supply amplifier configuration. See a simulation circuit with similar RC4558. Please notice that these OPs have no guaranteed common mode voltage range for +/-4V supply, the simulation is based on typical values. The LTspice circuit is also attached.

    Attachment 157799
    we are discussing the latter question, because i want to make sure i can amplify the signal. so if i use njm4558 in a non-inverting single supply amplifier configuration that will amplify a positive input voltage that is greater than 1 volt?



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    Re: how to boost microvolts to higher voltages?

    The NJM4558 inputs do not work if their voltage is within a few volts from ground in a non-inverting single supply amplifier configuration.

    If the NJM4558 opamp has a positive and negative supply, then it can amplify an input from 0V to 3V less than its positive supply voltage. But some of them have inputs that work up to only 1V less than the positive supply voltage.



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    Re: how to boost microvolts to higher voltages?

    nobody has answered my question. KlausST said voltage at +IN node is 0V (this means that this input is connected to a supply rail. This violates your Opamp's specification, because your's is no Rail-to-rail input type.--> see "Input Common Mode Voltage Range")

    so you are saying if i use a dual supply that will fix the second issue? if i use both a postive supply voltage and negative supply voltage that will fix the second issue? sorry i am having trouble understanding how to fix the second isssue. could somebody answer the question? will that fix the second issue?



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    Re: how to boost microvolts to higher voltages?

    Hi,

    so you are saying if i use a dual supply that will fix the second issue? i
    There is no answer, because there is a lack of information.

    * what do you define as 0V_node?
    * where is +IN connected.

    --> draw a clear and complete schematic, where we can see "0V" and the connection of "+In".

    Klaus
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  5. #45
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    Re: how to boost microvolts to higher voltages?

    this is a schematic of the circuit
    Click image for larger version. 

Name:	aa6f2c13-74cf-4058-af3c-9e8639f64363.jpeg 
Views:	3 
Size:	122.8 KB 
ID:	157816

    0v is the negative terminal. and +in is connected to the negative terminal. i think i am using a single supply power source. so will a dual supply power source work?



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    Re: how to boost microvolts to higher voltages?

    Hi.

    Why don't you draw the dual supply?
    ... when you want to discuss about...

    Klaus
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    Re: how to boost microvolts to higher voltages?

    Hi,

    Quote Originally Posted by dl09 View Post
    this is a schematic of the circuit
    Click image for larger version. 

Name:	aa6f2c13-74cf-4058-af3c-9e8639f64363.jpeg 
Views:	3 
Size:	122.8 KB 
ID:	157816

    0v is the negative terminal. and +in is connected to the negative terminal. i think i am using a single supply power source. so will a dual supply power source work?
    Yes, it would. Remember, your op amp inputs need to be 'x' volts above ground. Read about mid-supply biasing to correct what's wrong with the schematic or use a dual supply to make sure the non-inverting op amp input (the 'plus' op amp input) is receiving a signal within its common-mode input range.

    The circuit is still an inverting amplifier, Vout = (-R2/R1) * Vin. Single supply can't go lower than its floor of 0V to generate a negative voltage... Why is the op amp inverting input also connected to the battery negative/0V or is that just what the picture makes it look like?



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    Re: how to boost microvolts to higher voltages?

    inverting terminal is not suppose to be connected to the negative terminal of the supply battery. sorry that is a mistake i made.



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    Re: how to boost microvolts to higher voltages?

    nobody has answered my question.
    I believe, you either don't read the answers or don't understand it. I have no other explanation for seeing the circuit in post #45 that has been already recognized as non-working. If you want to change it into a dual supply circuit, why you don't sketch it so?

    so if i use njm4558 in a non-inverting single supply amplifier configuration that will amplify a positive input voltage that is greater than 1 volt?
    Yes, if you refer to typical OP specs. Not necessarily, if you rely on guaranteed parameters. I presume you read the datasheet and noticed the difference between typical and minimal voltage values, also the lack of specifications for +/-4 V supply.

    If you want a circuit that works by design, you should use an OP with complete low voltage specification.



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    Re: how to boost microvolts to higher voltages?

    Quote Originally Posted by dl09 View Post
    nobody has answered my question.

    Audioguru did in the previous post.
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    If you feel that I've helped you, please indicate it as a Helpful Post



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