NE5532 OP AMP faulty operation/overheating

Thread Starter

marcinlecki

Joined Apr 15, 2021
2
Good Day.
My goal is to make simple voltage follower based on OP AMP NE5532.
I have PWM signal of amplitude 0 - 10.35 V which I want cut to 0 - 5.25 or something like that (5.1-5.5 V max).
My idea was to supply 5.1 - 5.5 V voltage (VCC +) to OP AMP, which should cut the output voltage to approx. 5 V.
PWM signal (V2) is generated by National Instruments Card to which voltage is supplied by the same ac/dc power adapter as to voltage divider (R1, R2).
The schematic depiction of circuit is given below. I have run the simulation in circuitlab and it has worked in theory.
scheme.png
The actual circuit on Bread Board is given below with the pinout of the OP AMP. The first and the second pins are shorted. At the third pin PWM signal is fed. Fourth connected to the ground. Eight pin is connected to voltage divider made of two 18 kohm resistors. The middle voltage in voltage divider is about 5.25 V as measured before connecting it to 8 pin. There are additional two wires for the measurement of the output signal. They are connected to high impedance voltage measurement card. After testing the system I get unusuall behaviour - even the VCC+ is 5.25 V I get full 10.35 - 0 V signal and when I measure 8 pin voltage it oscillates, as the voltage from output was present there. After rewiring one more time, I get good output signal but OP AMP becomes quickly hot to touch which is unusuall because there should not be any haigh currents there and tested input isgnal is a low frequancy one. Could give me some ideas what is wrong here?IMG_20210414_161012.jpg1618532047368.png
 

Veracohr

Joined Jan 3, 2011
759
The inputs of the opamp have protection diodes to the supply pins. If there’s no current limiting between the source & the opamp input, it’s going to draw extra current through that diode.
 

crutschow

Joined Mar 14, 2008
27,761
I have PWM signal of amplitude 0 - 10.35 V which I want cut to 0 - 5.25 or something like that
Why use an op amp for that?
Just use a voltage divider/attenuator to reduce the signal amplitude.
Using two equal value resistors (e.g. 10k and 10k) will reduce the amplitude by a factor of 1/2, so 0 - 10.35V will become 0 - 5.175V.

If you need a lower output impedance, you can use the op amp as a non-inverting follower.
 
Last edited:

DickCappels

Joined Aug 21, 2008
7,746
I think we can propose a circuit that is likely to help if you can provide a little bit of information:
What this circuit supposed to drive?
What is the maxiumum desired output voltage?
What is the minimum desired output voltage?
What types of op amps are available to you?
 

Thread Starter

marcinlecki

Joined Apr 15, 2021
2
Hello, thank you guys for so quick answers and tips.
For the overheating I should try to put resistor between signal source and 1 IN+ pin to reduce current (as I understand it).
Why I decided to use OP AMP instead of voltage divider?
I use the OP AMP to deal with PWM signal because (as I read at other forum) voltage divider can not always output 1/2 of voltage (in the case of equal resistors) at higher frequencies (there can be some voltage peaks). 1 Hz frequency is just for initial test - I need higher frequencies.
At that forum thread they suggested voltage divider with zener diode for cutting voltage if its out of amplitude, or another idea was to use OP AMP. I had some OP AMP so...
Now I think I was too careful and I shoul use just a voltage divider.

Maybe to clear if I really need op amp, I answer @DickCappels questions:

the output of OP AMP should drive Toshiba TB67S249FTG stepper motor driver:

"Logic input pin voltage: GND≤ VIN1 (L) ≤ 0.8 V 2.0 V ≤ VIN1 (H)≤ 5.5 V"

so I want to control the speed of a stepper motor.

Maximum output voltage is as stated in VIN1 (H): 5.5V.

Minimum is 0 V, I do not know how stepper motor driver would react to negative voltage.

Maybe I have different OP AMPs, I would have to search my stash.

Obviously in using OP AMP as voltage follower I have ignored resistances as shown in schematic from documentation below.
1618583130812.png
Also as beginner I do not know if voltage as power supply to OP AMP (between VCC+ and VCC-) is not too low (5.25 V and 0V)?
 

ElectricSpidey

Joined Dec 2, 2017
1,815
The image you just posted in not a follower, it's configured with gain.

Your amp may be overheating due to oscillations do you have the proper de-coupling caps installed...I don't see any on the BB.
 
Last edited:

Ian0

Joined Aug 7, 2020
3,281
Toshiba TB67S249FTG has a maximum input voltage of 5.5V, and Vih =2V. The input has a 100k pulldown.
The PWM signal has an amplitude of 10.35V.
A divide by 2 circuit is all that is necessary, which can consist of nothing other than a 100k resistor in series with the input.
(Which forms a divide by 2 in conjunction with the 100k pulldown)
 
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