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OPA2365: Making a Voltage Sensor with High Precision

Farzaneh Faridi
Intellectual 585 points
Part Number: OPA2365
Other Parts Discussed in Thread: TIPD127,

Dear members,

We supposed to use a high precision voltage sensor in one of our products but we couldn't find what we really need to buy and then we decided to make a one ourselves. We used two TI tutorials:

1- Analog Pulse Width Modulation for making the PWM in fuction of input voltage "www.ti.com/lit/ug/slau508/slau508.pdf?ts=1682608456773"

2- Micro controller PWM to 12 bits Analog out as the DAC. "www.ti.com/.../TIPD127

I have a bunch of questions about it and I will appreciate deeply if anybody can help me, 

Requirements:

I need to make a sensor to sense 0 to 6KV DC voltage. The Switching frequency is 500KHz. 

You can find the SCH of what I have done so far:

for the DAC part I used the TINA simulation and I changed the values to what I supposed they could be working for us. 

I haven't put the fiber optic dirver and powersupply parts yet. But the idea is to generate the PWM and then connect it to DAC via a fiber optic. 

Doubts

1- I used the resistors to reduce the voltage. But as it obvious the power dissipation will be too much on each one. is it necessary to use the opto-amplifier?

2- The tutorials were done to make a PWM of a biopolar signal while mine is a DC one so no need to have an OFFSET but I'm not sure if it's going to work as we expect.

any suggestion would be deeply welcomed.

Farzaneh

  • 0
    Guru 140200 points

    Hi Farzaneh,

    at the input I see a voltage divider setting the 6kV down to 0.5V? And a time constant of 127R x 330nF giving a low pass filter of 3.8kHz? What is the bandwidth of your input signal?

    And the PWM generator is wished because you only want to use one fiber cable to transmit the signal out of the high voltage area? You could use a standard ADC with SPI bus but would need more than one fiber cable then, which you do not want?

    Is this correct?

    Kai

  • 0 in reply to kai klaas69
    Intellectual 585 points

    Dear Kai,

    My sensor sould be capable of sensing 0 to 4000V and up to 6000V in transient. For the BW still no idea and the values are not set definitively. And for the fiber optic, yes we wanna use only one (cost issues) to connect the PWM generator to the 4th grade filter of the DAC and then amplifying the ripple to make it measurable by an OSC. 

    My general big question is that: Can I use these tutorials for making a PMW and then DAC from a DC input which is 0 to 6000V? Because ther are already done for alternate inputs.

    By the way I reduce the input voltage to 0.5V because the opto-amplifier has a gain of 8.2.

    Regards

    Farzaneh

  • 0 in reply to Farzaneh Faridi
    TI__Mastermind 25415 points

    Hello Farzaneh, 

      What is the expected input voltage range to the OPA2365?

       Is the TLP7820 opto-amplifier for current sensing or is the main purpose of the application to attenuate a high input voltage signal (up to 6000V DC) down to 0.5V DC then generating a pulse-width-modulated (PWM) waveform of 500KHz? If the later, I agree with the opto-amplifier not being necessary. 

    Thank you,

    Sima 

  • 0 in reply to Sima Jalaleddine
    Intellectual 585 points

    Dear Sima,

    Our micro will be working with 3V. so firstly, I wanted to reduce the voltage using the sense resistors to 3V and then directly use the OPA 2365. Without the opto. 

    I used opto just to seprate the high voltage. on the other hand, we use this opto when we have alternate voltage and here we will be working with DC. So, I'm not sure if I should use it or not.

    Thanks

    Farzaneh

  • 0 in reply to Farzaneh Faridi
    TI__Mastermind 25415 points

    Hello Farzaneh,

      The OPA2365 is a RRIO amplifier which can accept 3V DC voltage. Do you have simulation of the PWM stage? 

      The opto amplifier you have chosen does provide isolation, but I would suggest a voltage sense isolation amplifier instead if you require protection from rest of the signal chain or other common faults. 

    Thank you,
    Sima