When a lm358 chip is used as a subtractor and a voltage follower, the chip will get hot and generate heat. Don’t know what went wrong? ? ? When the voltage follower is not connected, the chip will not heat up. When the voltage follower is connected, the chip will become hot. Is it a voltage follower problem? ? Or is it caused by the subtractor and the voltage follower together? ? ?
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It may help to use normal opamp symbols if you want your question to be answered quickly.
I agree. I work with op amps routinely but I would need to redraw what I see in order to understand it easily. Redrawing it might even help Cecilia_Qiu to see the error of her/his own ways.
Hello and welcome @Cecelia_Qiu
This forum is primarily about the use of Kicad, but many are willing to help with circuit design.
The usual way to draw this circuit is with discreet Opamps, Vee at the bottom, Gnd in the middle and Vcc up top.
A few questions:
What is the value of Vcc?
What is the value of Vee?
What is the input voltage range?
Have you ever used this IC before for bread-boarding?
Did you connect the IC correctly before applying power?
Good questions. One other point is that I see no power supply bypass capacitor. LM358 is not so demanding but most ICs can misbehave without adequate bypassing of the power rails. The IC could be oscillating; an oscilloscope would be best to indicate that.
Another important question is what is the load that is applied to the output? Too much capacitance in the load can cause oscillation. Too much load current can also overheat the chip.
Another idea is to send 1-2 close-up photos of the IC on the board. In place of that, an image of your pcb layout might be helpful.
And yeah… what is the load impedance ?
I think you miswired something. First draw a good schematic and double check the pins against the datasheet. With the schematic check that the operation point of the circuit is as designed. Then check that your physical wiring matches the schematic.
I learned many years ago that some (maybe many?) op amps will oscillate when directly driving a capacitive load. I would think that this could cause significant power consumption. It is possible to decouple the capacitive load from the op amp so as to “stabilize the beast.” These are some preliminary R-C values to try:
2K ohms in series between the op amp output and the load, and
10K ohms between the load and the op amp inverting input, and
10 nF connected between the op amp output and the inverting input.
This approach would be suitable for DC or slowly varying outputs only. For example if you have Vref = 2.5 and you use a 10K divider to make Vref = 1.0. Then you need to follow this reference voltage to handle 1 mA dynamic load current.
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