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LM324: Struck with Circuit to measure -15VDC to +15VDC analog voltage

Intellectual 390 points

Replies: 20

Views: 160

Part Number: LM324

Hi,

 

We need to measure both Negative and Positive analog Voltage range from -15VDC to +15VDC in the same pin. Measured Voltage should be displayed on the LCD.

 

We know only Inverter circuit and Voltage Follower individually.

But we don't know the circuit to measure both Positive and Negative Voltage. Kindly suggest/Provide circuit/schematic for this.

 

Is it possible to implement this on LM324 or could you suggest better part ?

 

Kindly share Schematic for this application or Kindly advise us How to Proceed for the implementation.

 

Thanks & Regards,

Naveen K

  • Hello Naveen,

    For non-inverting, see my blog on voltage scaling. The excel calculator picks components for the voltage scaling.  

    Three ways to scale an analog input signal

    Download the three resistor scaler Excel calculator.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hi Ronald,

    Thank you very much for the suggestions, We are using Solution#3 without amplifier for CT application to scale up. We are having some doubts for this application.

     Kindly provide your support for all the questions individually for more understanding.

    1. Can we use Clamping circuit as shown image instead of Solution#2 or #3 ? Clamping circuit is only for AC or it can also be used for DC ?

    2. Regarding to Solution #2, Why gain circuit (we can avoid 80K,10K on inverting input) is required instead of Voltage Follower here? Without gain, output will 0 to 2.222, with gain 0 to 2.5V. What is key advantage for adding gain circuit?

    3. Solution#2 and Solution#3 both scaling circuits are same right? Only Resistors values differ. For both the cases amplifier is optional right?

    4. Amplifier is Optional, but it may be used for current gain right? Current gain is necessary here or is there any key advantage?

    5. Figure-7, amplifier output will be 0 to 5.8V(due to VDD=3.3V, it will clip to 3.3V)) not 0 to 2.5V right?

    6. Iam thinking to go with figure 8 with some modification as shown. Kindly suggest which one is more efficient A. Voltage Follower or B. With Gain?

    Thanks and Regards,

    Naveen K

  • In reply to Naveen K1:

    Naveen,

    1) Clamping circuit is to level correct a AC signal whose DC level is lost. The most popular example is restoring the horizontal sync pulses in analog television. Clearly the input series capacitor totally blocks DC voltage.

    2) There is no advantage to blog solution 2 unless gain is really needed. For example if solution 3 has no real solution.

    3) Solution 2 requires and op amp. Solution 3 does not mandate using an op amp. 

    4) The op amp buffer prevents output load (not known) from changing the scaling function. 

    5) Forget about figure 7; It is just there to make sure the were TI parts in the blog. Otherwise it would only be about resistors.

    6) 'A' is better when using a rail to rail input & output op amp. 

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hi Ronald,

     

    Thank you very much for your advise and appreciate your quick response.

     

    1. Is there any other alternative methods except Solution#1(Need –Ve supply, -ve Resistor), Solution#2/3(Need ~3.3V supply to non-inverting pin)?

     2. Iam having doubt here, The same input signal(-15V to +15V) is reading by some other device(Master as shown in Figure1/2/3) and we(Slave-Device) are also using . We are scaling-up the signal by adding ~3.3V voltage Supply.

    Whether these things will effect to the behavior of the signal and it will cause to the reading operation of the microcontroller in the Master-Device?

    3. Our Scaling function should not modify the signal level/values in the Master-Device and the microcontroller reading operation should be same as before(Without SLAVE-DEVICE). So Kindly confirm it(Slave-Device) will not effect to Master-DEVICE and Master-Device will work as before like without SLAVE-Device right?.

     4. Master-Device GND, Slave-Device GND, Amplifier Ground, all 3 Grounds should be connect right?

    5. If we connect Master Device GND and Slave-Devise GND, there is No isolation like optocouplers right?Is it possible to make isolation?

    6. Without Master-Device GND, Amplifier will not work right?

    7. For over input voltage protection & ESD protection, where i can place the Diode. Figure 1 is correct or 2 is correct? Figure-1,Higher voltage will effects the Slave-Device including amplifier, microcontrollers right? Can you suggest protection diode?

    8. How i can protect from more negative voltage like -20V?Is it possible or i have to consider this in scalup calculations only?

    9. Figure1,2,3 Which one you will suggest?

    Sorry for some basic questions, i need your confirmation. Kindly advise.

     

    Thanks and Regards,

    Naveen K

  • In reply to Naveen K1:

    Naveen,

    I select figure 1 and make the resistors 10X bigger, 100k and 22k. Add a 1nF capacitor across D2. The op amp will be protected from +/-20V , even +/-50V. Now change LM324 to a TLV9001 instead. LM324 is not rail to rail on input nor the outputs.

     

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hi Ronald,

     

    Thank you very much for your all advise and appreciate your support. You have supported for all my query it will great helpful. This project is very important, i should not make single mistake. This is my last query which is also sent in previous text.  Kindly help us with individual answers.

     

    1. Is there any other alternative methods except Solution#1(Need –Ve supply, -ve Resistor), Solution#2/3(Need ~3.3V supply to non-inverting pin)?

     2. Iam having doubt here, The same input signal(-15V to +15V) is reading by some other device(Master as shown in Figure1/2/3 above) and we(Slave-Device) are also using . We are scaling-up the signal by adding ~3.3V voltage Supply.

    Whether these scalup function will effect to the behavior of the signal in the master -Device and it will cause to the reading operation of the microcontroller in the Master-Device?

    3. Our Scaling function should not modify the signal level/values in the Master-Device and the microcontroller reading operation should be same as before(Without SLAVE-DEVICE). So Kindly confirm it(Slave-Device) will not effect to Master-DEVICE and Master-Device will work as before like without SLAVE-Device right?.

     4. Master-Device GND, Slave-Device GND, Amplifier Ground, all 3 Grounds should be connect right?

    5. If we connect Master Device GND and Slave-Devise GND, there is No isolation like optocouplers right?Is it possible to make isolation?

    6. Without Master-Device GND, Amplifier will not work right?

    7. As you suggested, we will go with Figure 1 with multiply 10X to all Resistor's(100K,22K,22K),TLV9001.

    If >3.3V comes on point 1,it will go through D1 to Device VDD. It will not effect to the Slave-Device including amplifier, microcontrollers right? Can you suggest protection(ESD) diode?

    Thanks and Regards,

    Naveen K

  • In reply to Naveen K1:

    Naveen,

    The simulation answers most of those questions. Here is normal usage output voltage, input current, and current to 3.3V supply. The circuit does draw some current that the master must supply (-150uA to +120uA). Is there a specification for allowable current draw?

    Below is same signals for over voltage input. 

    The ground is the return signal and must be connected. There is no isolation for the ground. The slave power should have some isolation so the slave ground can use the master ground. 

    TLV9001 pm15 to 3V.TSC

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hi Ronald,

    Thank you very much for your kind support.

    We are tapping the signal from amplifier output(LM224-4 Channel), Is per our customer confirmation We can drawn up to 1mA from Master Device. we need -150uA to +120uA. So nothing will happens to Master Device signal right?

    For isolating the Power can we use LC Filter as shown in the figure? or could you give any suggestions?

    For Signal and GND line we are using 330R ferite bead in series with Master and Slave device.

    Thanks & Regards,

    Naveen K

  • In reply to Naveen K1:

    Naveen,

    The draw is less than 1mA so the requirement is met. I see no reason to isolate the 3.3V power, but your circuit is acceptable.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hi Ronald,

    Thank you for the suggestions.

    I have very clear for everything now. I will go with the same circuit.

    For isolating the 3.3V or any signal, we need to use only Transformer Barrier right? Ferritebed is only for filtering right?Could you suggest any Isolation Barriers?

    Thanks and Regards,

    Naveen K

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