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Power Op Amp Help

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Iawia

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Hi,

I purchased a few L165 Power Op Amps recently. I am having difficulty getting them to work. Looking at the datasheet, I see that there is an option for 'unity gain' and another option for gain > 10. I am a bit confused. The unity gain works fine, as I hooked it up just as the schematic says, without a +- supply (I don't see any place for pins 3 & 5 on their schematic for unity gain). To get a gain, I figured I'd changed the feedback resistor to 31k and the input resistor to 10k, set the +-12v on the appropriate pins, but I fully rail to -10v when my input is 1v. If the gain is 3.1v, I should have 3.1v on my output.

What is happening? Is there another schematic for gain 1 < K < 10?

Specs:
Op amp L165
Supply -12v, +12v (pins 3 & 5 respectively)
input voltage 1v
R2 31k, R1 10k

Application: To control a motor up to 3 Amps from a 12 v supply. Or alternatively, if someone can offer a better op amp? However, I still would like to know why this is not working.
 

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Pin 3 and 5 are + and - supplies. Power common is ground, not just power applied between 3 & 5. Just like in first diagram.

First is non-inverting with gain = (R2+R1)/R1

Second is inverter amp with gain = R2/R1. The 1k across + & - is just for stability and has no effect on gain.

Output RC in series is for stability to provide load at high frequency.
 
Pin 3 and 5 are + and - supplies. Power common is ground, not just power applied between 3 & 5. Just like in first diagram.

First is non-inverting with gain = (R2+R1)/R1

Second is inverter amp with gain = R2/R1. The 1k across + & - is just for stability and has no effect on gain.

Output RC in series is for stability to provide load at high frequency.

HI RC,

The leads for pins 3 & 5 are not shown on the 'unity gain' schematic. I am assuming I will need to hook them up for a higher gain than unity, so that's what I did. Then instead of using the 10K resistors, I used a 31k and 10k, and my output simply railed to -10 volts immediately. My output should be -3.1v. I have tried it on two brand new L165s, and figured I would ask you guys before I ruin the last one. I also threw on a heat sink because it was getting pretty hot.
 
The horizontal bar symbol - must be tied to the center tap between the +Vs and the -Vs supplies. You must run the examples shown on a dual, split supplies, e.g. +12V and -12V; not a single 24v supply.
 
Mike I have a bipolar supply. I have a volt meter and checked them both having correct polarity (-12v, +12v). Please check my setup. I also have the current limiter all the up.

I tied the '+' of the op amp to the green plugs, not the '-'. Is that wrong? I thought the non-inverting input must be grounded.
 

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Get rid of the Yellow jumper wire?

The green jack on the top supply is likely building power ground, and maybe interacting in some strange way with the bottom supply?

There should be a total of four wires going to the DUT. +12, 0V, -12V and 1V, where the 1V is referenced to the tap between the two 12V supplies (0v).
 
That didn't work. Output still rails to 11v. Can you suggest another op amp?
Another thing is that the schematic on the gain>10 has pin one on the non-inverting input, on the unity gain schematic, it has pin 1 as the inverting input. How can it be both? That's why I am not convinced this is the best op amp. Am I looking at this the wrong way?
 
I still don't understand. I've spent 8 hours today trying to get it to work. This sucks.
 
The datasheet has inconsistent numbering of the inverting and non-inverting input pins 1 and 2, which doesn't help. I'm inclined to believe Fig 1 rather than Fig 2.
If the top box in post #5 is a dual supply with the green centre connector being 0V, red being +V and black being -V, then you've got both the 0V and -V rails connected together at the G input on the lower box!
 
The op amp must have plus and minus supplies with the common point of the supplies being the common point of you circuit. If not you will get strange results
 
assuming you have two 12V power supplies you would connect the two supplies in series(the (+) terminal of one supply to the (-) terminal of the other supply). the junction between the two supplies becomes the center ground, the open (-) terminal is the negative rail, and the open (+) terminal is the positive rail, and you don't need so many banana jumpers, and ignore the green ones for now.

once you have it connected that way, you should have 24V between the open (-) and (+) terminals, and 12V between either of the open terminals and the center connection
 
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I think people are confused by your green plug being DC ground. So you want to hook it up like Fig. 1 not Fig. 2. You should make it exactly the same - no fair not using all the parts except the diodes. :D Then if it doesn't work measure the voltages at each pin for us. (Fig. 2 has the wrong pin called out for +/_ inputs like Alec noted.
 
Fig. 2 has the wrong pin called out for +/_ inputs like Alec noted.
Why does ST Micro hire stupid little kids to do their wrong datasheets?? Doesn't an engineer check their datasheets for errors??
 
1) They're cheap. 2) Apparently not :D
 
assuming you have two 12V power supplies you would connect the two supplies in series(the (+) terminal of one supply to the (-) terminal of the other supply). the junction between the two supplies becomes the center ground, the open (-) terminal is the negative rail, and the open (+) terminal is the positive rail, and you don't need so many banana jumpers, and ignore the green ones for now.

once you have it connected that way, you should have 24V between the open (-) and (+) terminals, and 12V between either of the open terminals and the center connection

Hi,

Unclejed613 and all others who have responded, this is exactly how I hooked it up. I have a +12 v comin from the red terminal, and a -12 coming from the black terminal. The center terminal (green), I tested with the volt meter to be +/- 12 volts between the two terminals. The input voltage (1v) from the top power supply is red. The black terminal of the input, I connect to the center green tap. Is this the correct setup for my power supplies???

I also tried another brand (texas instur), OPA548 and it still did not work. So I am really confused why its not working. I tried UA741s and they responded well. I put together a PI control with these supplies (+/-) 12 v, but the power op amps are not working. Please help!

Please advise,
-t
 
Is it wired as below? Note where "ground" is and all the things that are connected to it. Trace every wire...
 

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Ok. Thanks a bunch Mike. I will set it up once I get back to school. I noticed you have R5 (1k), a C1 (.22uF) and an R3 (1 ohm). These look like things that protect or condition the signal. Is this correct? I a very curious as to what these do. I will let you know what happens. Thanks!
 
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