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2302 External Feedback Loop Failure

2302, 2303, 2303-PJ, 2304, 2306, 2306-PJ, 2306-VS, 2308
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Joined: October 5th, 2015, 11:29 am
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2302 External Feedback Loop Failure

Post by [email protected] » October 5th, 2015, 11:56 am

Fried a couple of DUTs on our new 2302 last week and had some questions.

Setup:
  • Configured system output voltage and impedance (DCR) 2.4V and about 0.500 Ohms respectively.
  • Ran the sense leads close to the DUT to use four wire sensing and to factor for line loss.
  • Didn't care too much about contact resistance for this quick test so clipped Sense+ and Source+ together near the load and clipped Sense- and Source- together near the load.
What Happened:
  • Fried the DUT (and fried right through the zener clamp in the system)
  • Put a DVM on the circuit and saw a voltage spike at least as high as 15V (scope wasn't handy)
What Probably Happened:
  • Sense leads were loose or not connected. System thought it was only outputting 0V and cranked up the power looking for a rise in the sense voltage.
Questions:
  • Does the "What Probably Happened" hypothesis sound likely?
  • Is there an additional feedback loop internal to the system that can be used to protect against this? Ideally would want to set a maximum open circuit voltage as a level of protection?
  • Anything else that could have caused this?
Regards,

Nathan

Dale C
Keithley Applications
Keithley Applications
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Re: 2302 External Feedback Loop Failure

Post by Dale C » October 5th, 2015, 12:33 pm

Sorry to hear the device was "fried".
You are correct.
The sense lines must be connected or it goes in to a feedback loops that tries to compensate for the large impedance in the sense lines.
If you notice any connection diagram in the manual all of them have the sense lines connected either at the instrument or at the load.

[email protected]
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Re: 2302 External Feedback Loop Failure

Post by [email protected] » October 5th, 2015, 12:35 pm

So to confirm there is no secondary internal feedback loop to set a max OCV as a backup? Does the max voltage setting also use the external sense leads for regulation?

I should note that the sense leads were clipped on but the the clips we had on hand were too big for the gauge of wire we're trying to grab. Trying with grabbers next.

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Joined: October 5th, 2015, 11:29 am
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Re: 2302 External Feedback Loop Failure

Post by [email protected] » October 5th, 2015, 1:35 pm

Ok, think I discovered that VOLT PROTECT is the answer as it uses an internal feedback loop and protects when a sense lead comes loose.

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