Author Topic: Can I use a Lab Bench PSU and a Function Generator at the same time?  (Read 5027 times)

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Offline codingwithethanolTopic starter

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Long story short, I want to experiment with Op Amps; can I feed the rails with my PSU and the inputs with my function generator? I've read enough to know that hooking equip up wrong can lead to explosions and fire and all sorts of nasty stuff, so I just want to be sure that one wont back feed the other and fry it. Also how would you probe the output with an O-scope?
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Offline xrunner

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codingwithethanol,

Yes you sure can do that. Don't hook the signal generator directly to the power supply though.  :-+
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Offline codingwithethanolTopic starter

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Ok cool, just one question about the output, what would be its ground reference? I want to view the output on my oscilloscope. I would think it would just be the ground of the psu but theres feedback so im not sure.
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Offline xavier60

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Long story short, I want to experiment with Op Amps; can I feed the rails with my PSU and the inputs with my function generator? I've read enough to know that hooking equip up wrong can lead to explosions and fire and all sorts of nasty stuff, so I just want to be sure that one wont back feed the other and fry it. Also how would you probe the output with an O-scope?
You are uncertain as to how to power the op-amp and what to use as the ground reference.
Research "op amp single supply vs dual supply"
I suggest single rail for starters. You could wire a resistor in series with the output of the function generator to protect it, 1KΩ or higher.

More: I see that the PSU is dual channel, I still suggest staying with single rail for now.
« Last Edit: May 25, 2019, 01:54:45 am by xavier60 »
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 
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Offline xavier60

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I'm starting to change my mind. Although dual rail can be confusing for a beginner, single rail has its own messy complications.
Anyways, show us a diagram of what you want to try.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline codingwithethanolTopic starter

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xavier60,

Front page:    http://prntscr.com/nt2afu
Pinout:           http://prntscr.com/nt2alq

This is the data sheet for the op amp I have

Sketch:          http://prntscr.com/nt2dbg

This is a badly drawn sketch of the circuit I want to create, so I can verify signal gain on my oscilloscope   
[edit] I changed the sketch to incorporate the suggested 1k ohm resistor
« Last Edit: May 25, 2019, 02:24:30 am by codingwithethanol »
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Offline xavier60

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Some of the pin numbers on the op-amp symbol are wrong. Don't use the offset pins.
Where the positive and negative of the 2 PSU channels connect together, becomes 0V and also the ground reference for all measurements, also the ground connection for the function generator.
Make certain that any output DC offset adjustment on the function generator is set to zero volts for now. Use a lower output level for now.
I used Diptrace to draw the schematic. The limited use version is free to get. Or if someone knows of a more suitable drawing application.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline xavier60

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±5V is the minimum supply voltage for the UA741. After the circuit is working, increase the supply to ±10V.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline David Hess

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Yes, sort of.

Just be aware that the output of the function generator is not isolated so the BNC ground is the same as the chassis ground of the power supply.  This is not a problem if the power supply output is floating which is common but there will still be considerable capacitance between the power supply output and chassis ground.

 

Offline codingwithethanolTopic starter

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Ok, im going to run to the store and grab some snacks before it closes, and then im going to breadboard the circuit and test it. Results coming up in ~20 minutes
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Offline codingwithethanolTopic starter

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #10 on: May 25, 2019, 04:51:22 am »
xavier60,

I apologize, that was a bit longer than 20 minutes (alot longer)
The max my unit can do is 18V so im gonna keep it at 16V p-p so 8VAC

Here is the breadboarded circuit:
http://prntscr.com/nt39g1

I've set my function generator to ~1kHz, 3V p-p (1.5VAC), I am viewing the output on my oscilloscope without turning on the PSU and it looks rather unusual (top is function generator output, bottom is opamp output):
http://prntscr.com/nt39kt

[edit] Just so you know, I discovered that my opamps were actually produced by ST, and checked their datasheet
http://prntscr.com/nt3anq

Anyways, ready to flip the switch, hope nothing dies
« Last Edit: May 25, 2019, 04:57:25 am by codingwithethanol »
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Offline codingwithethanolTopic starter

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #11 on: May 25, 2019, 05:13:11 am »
Ok this is very unexpected:


I have no clue what could be causing this
An even bigger insult is that it doesnt even produce any gain
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Offline xavier60

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #12 on: May 25, 2019, 05:36:38 am »
You need to follow my diagram exactly. Both PSU channels are used, they are PS1 and PS2 in the diagram, wired in series just like two batteries might be wired in series. Use the red and black terminals, not the green ones.
Set each channel to 5V for now.
The op-amp wont do anything meaningful until powered up correctly.
I'll add more detail if I spot specific problems. 

Start with a much lower signal input level like 100mV p-p.
Correction: I see that they are white/black terminals for +/- on the PSU.
Extra: The op-amp will appear to function oddly if the Pot is at a particular one of its extreme settings. 
Leave it set near the middle until things stat to make sense.
« Last Edit: May 25, 2019, 06:07:24 am by xavier60 »
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline codingwithethanolTopic starter

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #13 on: May 25, 2019, 06:14:48 am »
Here is how i have the circuit wired to the PSU:
http://prntscr.com/nt3mjg

Ive seen people run both channels in series, I can probably do so if needed

I followed the schematic when breadboarding
Heres an annotated picture:
http://prntscr.com/nt3qdr

As I was annotating, I realized I had switched the inputs by accident, and switched them back
The output is relatively the same as before:
[edit] forgot to paste image link
http://prntscr.com/nt3rzu

Anyways, the minimum my function generator puts out is 2V p-p (1VAC), so ill make a voltage divider to get it lower
[edit] I just sweep the pot to test, the only thing that changes is the amplitude
« Last Edit: May 25, 2019, 06:18:27 am by codingwithethanol »
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Offline xavier60

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #14 on: May 25, 2019, 06:28:07 am »
Here is how i have the circuit wired to the PSU:
http://prntscr.com/nt3mjg

Although that's not the  correct way, it can be made to work, Connect a resistor from the + terminal to the green terminal. Connect another resistor of the same value from the - terminal to the green terminal. 1KΩ should do.
The idea is to balance the + and - rails. Measure the voltage of each rail with respect to ground, they should be about the same as each other.

More: Take the rail measurements at the pins of the op-amp. Also both input pins and output should be 0V.
« Last Edit: May 25, 2019, 06:31:18 am by xavier60 »
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline xavier60

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #15 on: May 25, 2019, 06:40:35 am »
The ground leads for the function generator and CRO must connect to the point that has the ground symbol in my diagram, no to the op-amp's inverting input.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline Brumby

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #16 on: May 25, 2019, 07:14:06 am »
This is a rough block diagram showing the basics of your supply and how it might typically be used for op-amp circuits.



Note:
 * The earth terminal is not connected to any of the output terminals - unless you make that connection yourself.
 * Each output should be set to the same voltage.  If your supply has dual tracking capability (I haven't checked the manual), then you can set both at the same time.
 * Many supplies also allow for both outputs to be paralleled internally for greater current output.  Make SURE this is not engaged!!!
« Last Edit: May 25, 2019, 07:17:58 am by Brumby »
 

Offline codingwithethanolTopic starter

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #17 on: May 25, 2019, 07:42:24 am »
The ground leads for the function generator and CRO must connect to the point that has the ground symbol in my diagram, no to the op-amp's inverting input.

But its AC? I dont understand how that would work
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Offline xavier60

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #18 on: May 25, 2019, 07:50:19 am »
The ground leads for the function generator and CRO must connect to the point that has the ground symbol in my diagram, no to the op-amp's inverting input.

But its AC? I dont understand how that would work
Yes, the signal from the function generator is usually AC, not always. Is that what you mean?
Everything has to be wired exactly as shown in my diagram to work properly.
On second thoughts about adding the 1KΩ resistors. If you haven't done it yet, It's best to use both PSU channels as explained. It is the preferred  way to implement dual rails.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline codingwithethanolTopic starter

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #19 on: May 25, 2019, 07:51:50 am »
This is a rough block diagram showing the basics of your supply and how it might typically be used for op-amp circuits.



Note:
 * The earth terminal is not connected to any of the output terminals - unless you make that connection yourself.
 * Each output should be set to the same voltage.  If your supply has dual tracking capability (I haven't checked the manual), then you can set both at the same time.
 * Many supplies also allow for both outputs to be paralleled internally for greater current output.  Make SURE this is not engaged!!!


I found this video of a guy testing a very similar supply with slightly different specs, it does have a tracking mode, and ill try this next
(Tomorrow, because its nearly 4am over here)
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Offline Brumby

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #20 on: May 25, 2019, 07:55:09 am »
The + and - inputs to the Op amp are different to the positive and negative markings on your power supply.

For an Op amp:
 - any signal applied to the + will cause the output to move in the same direction.  When the signal goes up, the output goes up and when the signal goes down, the output goes down.  The input signal usually goes in here.
 - any signal applied to the - will cause the output to move in the opposite direction.  When the signal goes up, the output goes down and when the signal goes down, the output goes up.  The feedback loop usually runs back into here.

The output from the signal generator will typically go to the + input and the 0V point in the diagram I posted above.
 

Offline codingwithethanolTopic starter

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #21 on: May 25, 2019, 07:58:11 am »
Yeah I pulled V+ and - to ground as well as the non-inverting output as in the schematic and im getting a flatline on my scope
Its getting late where I am so im going to drift off to sleep but ill be around tomorrow at the same time to wrap this little experiment up.
Thanks for your help so far, I appreciate it. I had been doing EE study before, but never really had enough equip to do anything beyond arduino gimmicks and blinking leds, so now that i do have a mini lab set up, im going to delve into more advanced stuff
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Offline xavier60

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #22 on: May 25, 2019, 08:43:14 am »
This diagram should remove all ambiguity.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline codingwithethanolTopic starter

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #23 on: May 30, 2019, 05:32:41 am »
Ok here's the scoop:

Never got it to work, as a matter of fact, while trying to figure out why the gain was literally negative, i turned off my PSU while looking at my oscilloscope and the output didn't change! Something else I discovered is that the second channel on my PSU is acting funny, I set it to 10V and it shows 4-5V with 4mA current with no load! Anyways, i've moved on to other things for the time being but ill come back to this issue eventually. Thanks to everyone who volunteered info, I learned quite a bit
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Offline james_s

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Re: Can I use a Lab Bench PSU and a Function Generator at the same time?
« Reply #24 on: May 30, 2019, 05:55:50 am »
It doesn't seem like you're listening to what anyone is saying, you're just flailing around and then reporting that it doesn't work. This is a very, very simple circuit, if you wire it up exactly as shown it will work. If your power supply is not working properly it may have been damaged but do make sure you're using it correctly first. Slow down and read the manual, follow instructions, if you just blindly wire stuff up without understanding the most basic aspects you are not going to learn much.
 


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