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I just purchased a DC bench power supply from Ebay. I have been trying to power up an op-amp circuit but with no luck. I checked the voltage of each output terminal with reference to the ground(earth ground) on the power supply. There is the correct positive potential but the negative terminal is showing no difference in potential as compared to ground. I am correct in believing this should show the negative 15V I am looking for and not 0V correct?

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closed as off-topic by Nick Alexeev Feb 16 '16 at 0:19

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Nick Alexeev
If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Please post a picture of the supply. Most supplies have both an earth ground and a supply ground, in which case the supply terminals may be floating many volts above or below earth ground. \$\endgroup\$ – uint128_t Feb 16 '16 at 0:00
  • \$\begingroup\$ Depends on the power supply. If it's a single rail PSU it may have 0V, 15V, and a separate Gnd which you can connect to either 0V or 15 (but obviously not both!) Picture will help. \$\endgroup\$ – Brian Drummond Feb 16 '16 at 0:04
  • \$\begingroup\$ You should post this question to the eBay seller. EE.SE is not his volunteer technical support. \$\endgroup\$ – Nick Alexeev Feb 16 '16 at 0:18
  • \$\begingroup\$ A lot of questions could be answered with "you should post this question to (the company that makes or sells the thing)." The question does not seem off-topic to me. It's not about consumer electronics or programming. There are a number of similar questions (like electronics.stackexchange.com/questions/146304/…) that were answered. \$\endgroup\$ – Willis Blackburn Feb 17 '16 at 2:55
  • \$\begingroup\$ @Willis (1 minor point) That other question which you have linked is clearer, better written, and even illustrated. (2 fundamental issue) The transaction was between the eBay seller and the O.P. The eBay seller profited. He should be pestered with technical support issues. EE.SE is not his volunteer technical support. \$\endgroup\$ – Nick Alexeev Feb 17 '16 at 7:21
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Your power supply has three terminals but they're not positive, negative, and ground, as you think. The red terminal is positive, the black terminal is 0V, and the green terminal is connected to the mains ground. The difference between the green terminal and black terminal is that the black terminal is only connected to a transformer, not to mains ground.

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Unless the supply has separately adjustable positive and negative voltages and currents, it probably is a unipolar supply with a separate earth ground, and can only supply a single voltage. For example, this one (randomly selected eBay listing):

enter image description here

If you want a second negative supply, you can buy another power supply and tie the (+) output of one to the (-) output of the other, and typically you'd connect the earth terminals together (usually the output floats with respect to earth ground).

You might want to tie the earth grounds to the common between the supplies (but not always).

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