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Lv 6
? asked in Science & MathematicsEngineering · 10 months ago

How to create a circuit to drive a 3 Phase BLDC Motor?

As the question stated. What I saw online was this, but I couldn't exactly understand why I needed 6 MOSFETs and not 3.

https://www.digikey.at/de/articles/how-to-power-an...

The circuit I had created was actually very similar to this. I have 3 IRF840 MOSFETs for the application, because it is a large motor. For this, I have connected an Arduino and programmed it basically to emulate a PWM with each output pin being on at their respective time for 20 ms (since I need 50 Hz as PWM). 

Now, since IRF840 requires a gate voltage of at least 10V, I'm going to connect low current/low voltage PNP transistors in cascade with each Power MOSFET, operating at 12V. So, basically, Arduino to control PNP transistors to Power MOSFETs. 

Below you'll see the circuit I found in the website I linked above. Now, here is my question. If I am to control this circuit with an Arduino, what exactly is the frequency that I need to use for each PWM input in the figure? Should it be 10 ms or 20 ms if I am to achieve 50 Hz, because from what I understood, one set of MOSFETs is affecting the North Magnetic pole whilst the other set of MOSFETs is affecting the South Magnetic Pole. Again, I can easily program this, but I just need to make sure. Note that I only need to run the motor on a single speed, so no need to add additional circuitry for dimming. 

Thank you all for your answers :)

Update:

One more question about this circuit... is this not in danger of a short circuit? I mean, the MOSFETs are being used as switches obviously, so without any resistors to go through them, short circuit could be a possibility. Note that the voltage is also no joke. It's 320 V and the current drawn is at least 5A (which is why I chose IRF840).

Attachment image

2 Answers

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  • 10 months ago
    Favourite answer

    You need 6 Fets because it is full wave control.

    If your control is reliable you will not have any shorts. The pulse width depends on the speed of the motor and the power needed.  Wider pulses will give more available power. Play with it and see what the effects are.

  • 10 months ago

    Because it was a full wave control circuit.

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