Hello everyone,

I am working on a project for an electronic variable load with a power MOSFET that can handle up to 10 A. To control the gate I need between 0-10 V, but since the ESP32 only outputs 3.3 V, I have set up a system with a DAC MCP4725 and a non-inverting operational amplifier with a gain of approximately 3. This way I can directly control the gate of the MOSFET without using a gate driver, since I am not looking for switching but rather to work in the linear region to perform Vgs sweeps and control the current.

The setup is as follows:






Since I added the diode at the gate, when looking at the oscilloscope there is noise on the signal before the diode (yellow trace in the capture). Then I checked the output of the DAC and I also see a rippled signal (pink trace). Interestingly, after the diode that noise does not appear, but the circuit does not work as expected, during the sweeps the Vgs is not very clean.


What could this noise be due to? Which components should I add or remove? I don’t understand what I am doing wrong in the setup.

 

How does the earth of the MCP4725 and MC33201 connect to the earth in the power circuit?

 

To control the gate I need between 0-10 V, but since the ESP32 only outputs 3.3 V,

Is the output from the ESP32 a PWM signal?

 

Q2, I don't see how any of that works. R23 must measure current but I can't see what current. Please show more of the circuit.
Does R23 connect to ground somehow?

 

How does the earth of the MCP4725 and MC33201 connect to the earth in the power circuit?

Yes, the ESP32 controls the DAC (MCP4725) via I2C, which is then amplified by the amplifier, and all are connected to the same GND, where the "INA-" is also connected to the GND (the MOSFET source).

 

Is the output from the ESP32 a PWM signal?

No, it communicates via I2C with a DAC that provides an analog signal, where the control signal is a ramp going from 3.3 V to 0, but this is amplified by a factor of 3 to range from 0 to 10 V, which is the appropriate voltage to drive the power MOSFET, since up to 10 A can flow through it.

 

Yes, the ESP32 controls the DAC (MCP4725) via I2C, which is then amplified by the amplifier, and all are connected to the same GND, where the "INA-" is also connected to the GND (the MOSFET source).

Why is that ground connection not on the circuit diagram? Please modify it so we can all know exactly how it connects.

 

Here I’m sharing the version that clarifies the assignments better.

 

No, it communicates via I2C with a DAC that provides an analog signal, where the control signal is a ramp going from 3.3 V to 0, but this is amplified by a factor of 3 to range from 0 to 10 V, which is the appropriate voltage to drive the power MOSFET, since up to 10 A can flow through it.

Which mosfet are you planning on using ?
I think you would see better results using PWM from the ESP32 which can easily be level shifted to 10 volts thus eliminating the DAC and op amp.

 

Here I’m sharing the version that clarifies the assignments better.

View attachment 355631

Great. But wasn't there an instrumentation amplifier? Where does the output of that go?

 

There is nothing in your post #8 circuit to monitor the voltage across the current sense resistor R23.

 

Which mosfet are you planning on using ?
I think you would see better results using PWM from the ESP32 which can easily be level shifted to 10 volts thus eliminating the DAC and op amp.

No, because I want to perform a sweep of a solar panel, carrying out the open-circuit and short-circuit tests, but in between I need to obtain its points. For that I have to enter the MOSFET’s saturation regio, I don’t want switching.

 

Great. But wasn't there an instrumentation amplifier? Where does the output of that go?

Yes, there is: an MC33201 amplifier in a non-inverting configuration with a gain of 3.

 

There is nothing in your post #8 circuit to monitor the voltage across the current sense resistor R23.

Yes, there is voltage and current monitoring to perform the test and obtain the P–V curve, but I did not include it because it is independent of my problem, since the issue I have is with the control of the MOSFET that performs the sweep (variable load).

 

Yes, there is: an MC33201 amplifier in a non-inverting configuration with a gain of 3.

MC33201 is just a plain old op-amp. What was IA+ and IA-?

 

MC33201 is just a plain old op-amp. What was IA+ and IA-?

To measure the shunt voltage, but here the measurement is not important, since it is independent and it works fine for me.

 

To measure the shunt voltage, but here the measurement is not important, since it is independent and it works fine for me.

So, you have noise on the output of the DAC. Do you have noise on the digital signal that goes into the DAC? Does the noise stop if you short SCL to ground (to disable the writing to the DAC)?

 

what is the signal shown as bottom trace?