Electronics > Beginners

Can I use a Lab Bench PSU and a Function Generator at the same time?

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codingwithethanol:
james_s,

"It doesn't seem like you're listening to what anyone is saying"

I followed xavier60's design to the tee after he made clear the circuit design. This whole thread was really the result of me not wanting to blow things up by shorting my equipment through earth ground as I have learned from EEVBlog and other enthusiasts. The posts here have been quite helpful in elaborating on the nature of the connections in the equipment.

"you're just flailing around and then reporting that it doesn't work"

Let me specify. My PSU went into overcurrent protection mode as I tested the circuit, and so I shut it down. I noticed that after I had, I was still seeing output from the opamp on my oscilloscope. This means the PSU was never powering it in the first place, and the oscilloscope was simply seeing the Function Generator output through the feedback resistors. Examining my PSU, I found that Channel 2 had been shorted and was reporting a fluctuating 4-5mA current when nothing was connected. I presume this to be an indicator that something had gone wrong with the protection circuitry, and so I am now limited to one channel until I can figure out what got burnt and replace it. In the meantime, I will be working on other things until I have a better understanding of what went wrong.

xavier60:
It's not easy to damage a well designed power supply as that one appears to be.  Have you had it for long?
It may have already had a fault.

codingwithethanol:
Yeah i've had for only a few weeks or so, didn't have a reason to use the second channel until recently but I thought I had tested it earlier.  It's actually quite likely it was already damaged or simply waiting to fail since I purchased it second hand for quite a reasonable price.

codingwithethanol:
As an addendum, I recently opened up my function generator to see what was inside and found that the BNC port grounds were also earth referenced. I checked a few other threads here and here are my main concerns.

1. Removing or simply taping over the ground pin on the power cable on the Function Generator would solve the issue of blowing up my oscilloscope but some people said it would probably lead to inaccurate operation or HV developing across the unused connectors which would obviously be a safety concern.

2. Always taking care to where the ground lead is placed is another solution but this limits what you can probe.

How can I make sure to protect my equipment and stay safe while still being able to probe around and experiment freely?

Zero999:
No, don't remove the earth connection to the oscilloscope. It's very dangerous, as it could float at a high voltage and cause electrocution.

Most power supplies have an adjustable current limit. Check it isn't sat to a very low level. Disconnect your op-amp circuit and connect a 1k resistor. The power supply should be able to supply 15V to 1k without current limiting. Check the manual for the power supply or search the net for the make and model number.

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