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OPA37: Need two groung level to simulation

Hank hung
Prodigy 10 points
Part Number: OPA37

Tool/software:

I need to simulate the charge circuit. That's a charge control circuit series connecting a cap.

But I can't simulate normally. Vshunt node keep sinking currnet through R9、R7、R13 to the ground

So the OPAs can't work properly. Even if I use two ground level gnd1 & gnd2

Could someone tell me how to fix it?

I will be grateful for any help you can provide.

  • 0
    TI__Guru 64071 points

    Hi Hank, 

    Could you provide me the requirement? It looks like that this is V-to-I converter. 

    Since I do not what you want, I post a V-I circuit to get you started. I need to know what you are trying to do. The example is my best circuit extraction. 

    OP37 V-I Conv 03282025.TSC

    If you have other questions, please let me know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 10 points

    Hi Raymond,

     

    This case is a V-to-I converter to charge C1.

    Because of the grounding level is not separated properly. The V-to-I converter flows current showing below.

    So I can’t control the voltage at Vshunt node. Am I right?

    Is any thing I can do?

     I will be grateful for any help you can provide. Thank you

    Load PS+C.TSC

  • 0 in reply to Hank hung
    TI__Guru 64071 points

    Hi Hank, 

    Hank hung said:
    So I can’t control the voltage at Vshunt node. Am I right?

    The circuit is saturated currently. You need to tell me what are the voltage values at each marked nodes. You have many unnecessary components in your circuit. What is your transfer function? In other words, what voltage is at input,  and what voltage is at output.  

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 10 points

    Hi Raymond,

     

    You can consider the circuit as a simple negative feedback control system.

    The voltage at Vshunt is derived from the input voltage VG1. First, VG1 is processed by operational amplifier U1, which applies a gain factor of 1/5. The output of U1 is then further amplified by U2, which applies a gain factor of 1/4. As a result, the final voltage appearing across Vshunt is a scaled-down version of VG1, following the combined gain factors of both operational amplifiers.

    If I remove the cap. C1(or turn on SW-SPST4). Vshunt is derived from VG1,that is 10mV in DC analysis.

    If C1 is increased, the negative feedback control will fail. I believe this is due to the ground reference.

    I will be grateful for any help you can provide. Thank you

  • 0 in reply to Hank hung
    TI__Guru 64071 points

    Hi Hank, 

    I know why the circuit did not work.

    I want you to provide me what is the input voltage range and what is output current range. What are the input circuit waveform and frequency? I need to know 设计的定位. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 10 points

    Hi Raymond,

    The input voltage of this circuit ranges from 0 to 4.5V, corresponding to a Vshunt voltage of 0 to 225mV, which means the current ranges from 0 to 4.5A. There is no frequency range; it operates in DC only.

  • 0 in reply to Hank hung
    TI__Guru 64071 points

    Hi Hank, 

    I did not get what you requirements are, but the circuit is operating linearly now. Please see if this is what you want. 

    Input: 0-4.5V --> we need to step down to 0 to 0.45V input range as an example. 

    Output: The current can be reduced, once the input signal Vg is reduced. Currently, it is very high. 

    OP37 Load PS+C 04022025.TSC

    For some reason, -LD node is a variable, so I fixed to 8.3Vdc. 

    If this is what you have in mind, we can readily modify the circuit to meet your requirements. Then we can check for the loop stability. 

    Best,

    Raymond