OPA2196: When increase input beyond 1.4V, Output keep at 0.67V and don't change.

Wentao Zeng

Part Number: OPA2196
Other Parts Discussed in Thread: TINA-TI

Hi Team

My customer have designed a curcuit to measure P+ and P-.voltage(+100V, -100V) .

When we input HV1 from 20V, it has normal output, But when input beyond 70V, Output keep at 0.67V. It should have face protection.

Do you have any suggestion for this case.

over 5 years ago

0 Alexander Davis over 5 years ago

TI__Expert 6250 points

Hi Wentao,
A couple of thoughts:

1. The clipping level of .67V seems very close to a typical diode forward voltage. Could you have the customer verify that D1 and D2 are installed with the correct polarity? If they were reversed, I'd expect a similar clamping behavior.

2. What is the purpose of C41 in this circuit? A simulation of this circuit in TINA-TI shows that the positive feedback provided by C41 makes this circuit marginally stable. It's possible for oscillations caused by this instability to appear as a DC error when measured with a DMM. Unless there's a design reason for adding C41, I'd recommend removing it.

3. The HVDC- circuit is unstable due to the large feedback resistance of R53 interacting with U2B's input capacitance. I'd recommend adding ~6.8pF of capacitance in parallel with R53 to resolve this.

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Wentao,

sorry, but this circuit looks totally weird. Please explain in detail how the circuit is intended to work. And please explain how "chassis" ground and AGND are connected to each other.

Kai

0 Wentao Zeng over 5 years ago in reply to Alexander Davis

TI__Prodigy 590 points

Thanks , Your are right, Diode result in it

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OPA2196: When increase input beyond 1.4V, Output keep at 0.67V and don't change.