I am not an electrical engineer. I am a mechanical engineer and trying to improve myself in electronics. So, if there is a silly question please forgive me :)
I am developing a 24V BLDC motor controller, which adjusts the motor speed via PWM that comes from another circuit. However, this PWM is 16-32V. I have to lower this voltage to 5V to read via my STM8A MCU. The PWM frequency is 100Hz.
My main goal is;
- Convert this PWM to 5V
- Invert the PWM to read LOW side as HIGH (I know we can solve it by software, but I would like to do it using hardware)
- MCU pulls (Edit: pulls to GND) the PWM line to send feedback (e.g. 1sec Gnd means overvoltage)
I saw a circuit online and made my own. (You can see it below.) But, I couldn't understand it completely.
- Why there is a 24V DC and R2 in this circuit?
- How can I know the PWM current?
- Do you think there is a problem with the circuit?
##Edit Insufficient information created misunderstanding. So, I'll try to give more detail.
My BLDC controller is for trucks. There are only 3 inputs for this controller. 24V (Truck battery voltage), GND and PWM. The controller consist of a MCU, gate driver, and h-bridge. There is a 5V regulator for MCU. PWM voltage is the same voltage as VBAT. It is typically 24V but I wrote the range of it. So, we can consider it as 24V.
My circuit should send some feedbacks to the ECU. Because there is only 1 pin for communication, I send the feedbacks by pulling the PWM line to GND. As you understand from the circuit, PWM should be 5V also my feedback is 5V. There are 6 error feedbacks and I can read all of them. They all have a specific time to be GND. For example, if the motor is stuck I pull the PWM to GND for 4sec, if there is overcurrent I pull PWM to GND for 1sec. So, my question is not about overvoltage protection or reading circuit, just sending feedback.
I have no information about the source impedance or PWM generator.
Also, the maximum working temperature for this circuit is 140°C. So, it is hard to find an optocoupler for these temperatures.