# Heating operational amplifier OP284FSZ-REEL7

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:

1. The amplifier is not designed for such a load or, conversely, it is not enough for it, and it begins to oscillate.
2. Is this an accurate amplifier, perhaps additional elements are needed for its operation?
3. The amplifier is damaged.

Parameters of currents from datasheets:

LM258WYDT

1. Input current: 5mA (DC)
2. Source output current (Isource): 20-60mA
3. Output sink current (Isink): 10-20mA

OP284FSZ-REEL7

1. Supply current: 2.25mA
2. Output current: 10mA

Question: What could be the reason?

What you are observing on the inverting input is a result of the type of op-amp you are using - a super-$$\\beta\$$ bipolar type. To protect the input transistors against reverse Vbe breakdown, they put diodes across the inputs. That's of little consequence in most op-amp circuits, however you are trying to use it as a comparator.