Electronics > Beginners
Heating operational amplifier OP284FSZ-REEL7
Glebiys:
Hello all,
Task: to make a square wave with a frequency of 1 kHz in the voltage range (-12V - + 12V), using a PWM signal with voltage (0V-5V).
Circuit:
Originally LM258WYDT (ST) was used as an operational amplifier, it did not heat up, but since it was not from the Rail-to-Rail series, there was a 1.5V drop at the output, which did not allow us to give out a voltage close to 12V. So I decided to switch to Rail-to-Rail, for these purposes I found OP284FSZ-REEL7 (AnalogDevices). After replacing with this amplifier, the value of the output voltage became close to 12V (+ -11.85V), but the operational amplifier began to heat up (after 5 minutes its temperature was about 45-60 degrees).
I did not find a short circuit, but noticed that at the output of the voltage divider (R1, R2), instead of 2.5V, the voltage became 4.5V. On the LM258WYDT, this voltage was 2.5V. Perhaps there are elements on this input of the operational amplifier that should lift it?
Unfortunately, at the moment I do not have an oscilloscope and I can not see the output signal.
My suspicions:
* The amplifier is not designed for such a load or, conversely, it is not enough for it, and it begins to oscillate.
* Is this an accurate amplifier, perhaps additional elements are needed for its operation?
* The amplifier is damaged.
Parameters of currents from datasheets:
LM258WYDT
* Input current: 5mA (DC)
* Source output current (Isource): 20-60mA
* Output sink current (Isink): 10-20mA
OP284FSZ-REEL7
* Supply current: 2.25mA
* Output current: 10mA
Question: What could be the reason?
TerminalJack505:
You might try attaching your circuit schematic again. I think you need to have 5 posts or more before you can attach files to your posts.
Glebiys:
TerminalJack505, thank you for the answer!
DuPe:
it is no good idea to use an linear op amp as comparator and even worse to use it without negative feedback.
Try a real comparator (http://www.ti.com/lit/ds/symlink/lm397.pdf) with recommened feedback circuit given on page 1.
cheers
Peter
Glebiys:
@DuPe, thank you for the answer!
At this stage, I have already created a printed circuit board, and it is impossible to remake it. I first encountered operational amplifiers. In the next version of the board, I will think about an alternative.
There is information:
The specification of the amplifier indicates the value of the Input voltage difference: 0.6 V, as I understand it, this is the maximum difference between the inverted and non-inverted input.
In my case, 2.4V (with a divider of 100k-100k) should come at the inverted input, and 5.1V should come at the non-inverted input. The difference between these voltages is 2.7V, which is clearly greater than 0.6V.
I see 4.5V, instead of 2.4V, which leads to the idea that he is trying to raise the voltage to 0.6V and because of this starts to heat up.
Current must be limited. The non-inverted input is connected directly to the microcontroller, which can output up to 20mA, and the inverted input to it comes with a divider, here I do not know if it can produce a current of more than 5mA, which destroy the opamp.
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