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Power amplfication problem with PWM signal

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Mr HG

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Hello ,

I designed a power amplifier so that it plays the role of interface between my STM32 microcontroller and a pump (12V 1A).

My problem here is this: As soon as I put my circuit power (+12 V GND-12V), the motor is running before I give him the PWM signal from my microcontroller. Then when I inject the PWM signal the peed of rotation increases.

Why the motor running before I put the PWM input?

Please give me a change in the circuit, so that the engine runs only when I give him the PWM signal ...

Can you help me ??

Here attached the circuit of the power amplifier.
 

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Bit of massive overkill as well :nailbiting:

You don't need a linear amplifier for PWM, just a simple switching circuit - it would also be a far better idea to has a PNP transistor feeding the motor rather than an NPN one (less loss, less heat).
 
For a linear amplifier, a TL082 in your circuit will not turn off the motor because a TL082 opamp has a problem called "Opamp Phase inversion". Look at the image I posted that shows the output when an input voltage too low.
When you want the motor to stop then you connect the input of the opamp to 0V. But if the opamp does not have a negative supply in addition to a positive supply (the opamps in your circuit DO NOT even have a power supply) then the input voltage is too close to the negative supply voltage (0V in your circuit?).

The datasheet for the TL082 shows that the input must be at least 4V more positive than the negative supply pin.

You can use an opamp that has inputs that work even when they are at the negative supply voltage and they are called "single supply" opamps. An old LM324 or LM358 are very slow ones or a TLE2141 is a fairly fast one.
 

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Thank you :)

So if I use LM324, I will solve my problem?

Can I use the same power supply for the amplifier (+12 V,-12V)?

Knowing that the PWM signal provided by the microcontroller STM32 is 3.3V , I want to have a good speed for my pump, which changes on resistances... ?
 
A lousy old LM324 was designed a long time ago to be the first low power quad opamp. To reduce its operating power they made it VERY slow. It has trouble with frequencies above only 2kHz.
Your motor will be heard whining and the output transistor will be hot.

A modern TLE2141 works perfectly with frequencies as high as 400kHz. Then you will not hear the motor.

If you use a plus and minus 12V supply for the TL082 dual opamp then it will work fine up to 100kHz.
Sorry, I did not see the power supply voltages on your schematic and I missed seeing them in your post.
 
Hello ,

I designed a power amplifier so that it plays the role of interface between my STM32 microcontroller and a pump (12V 1A).
This circuit is a good power amplifier which helped me to control this motor from the microcontroller which inject into the input a PWM 3.3V.

My question here is this:
I want to provide a more comfortable current (and voltage ) to the motor, so I change R1, or R9 or R6? and Why?

Vcc = 12V

Please give me a change in the circuit, so that the motor runs better.

Can you help me ??

Here attached the circuit of the power amplifier.
 

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  • power amplifier.jpg
    power amplifier.jpg
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It is horribly complicated for what you need to do. It can be done with about three parts if the switch can be low-side: a resistor, a logic level NFET, and a snubber diode. If one end of the motor must be grounded, then about five parts: a small NPN, a PFET, two resistors, and a snubber diode.
 
Last edited:
Thank you very much "andymei"

I have the schematic EAGLE size.

You can send me the modified circuit format PROTEL too.

I'm waiting for your answer.

Cordially.
 

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