Hello!
In the circuit I have a three phase MOSFET bridge to power a BLDC motor. (Not included in the picture). N-channel MOSFETs are not a problem to drive directly from the 3.3 V processor, as it delivers at least 20 mA of output GPIO current, which turns on and off the MOSFET fast enough and it opens the MOSFET enough as it is a logic-level MOSFET.
I have a problem at closing the P-channel MOSFETs. I have made 3 circuits to discuss advantages and disadvantages of each one.
Adding a MOSFET driver to the circuit would be a solution, but a more expensive one
Input comes from a processor pin.
Output is one of the three phases of the BLDC motor.
Option 1
Bipolar Push-pull option. Here the P-channel MOSFET doesn't completely turn off because of Vce voltage of the NPN transistor (around 0.8 V). This option would probably be OK, if MOSFETS were used instead of bipolar transistors (T1 and T2) as MOSFETS would have a much smaller Vds voltage.
Option 2
The NPN transistor T4 can close the P-MOSFET completly. But! In my understanding it can't provide more than 5V / 1kOhm = 5 mA of gate current, which closes the P-MOSFET too slowly for my application. The MOSFETS would get too hot.
If we decrease resistance of R3, then we get higher gate current, but losses on the resistor R3 get quite big ( P = U^2 / R ), which again is undesirable in this application.
Option 3
It is similar than option 2, just another resistor is added (R5), to limit the gate current when P-MOSFET it opening.
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My doubts are:
1) At option 3, would current go through R4 to close the P-MOSFET and through R5 to open the P-MOSFET?
2) Is there another good solution for this problem?
I hope I was clear enough
Your input is highly valued!
PN MOSFET datasheet:
https://www.diodes.com/assets/Datasheets/DMC1030UFDBQ.pdfSome MOSFET theory:
http://www.st.com/content/ccc/resource/technical/document/application_note/68/cd/c6/ab/ef/17/41/06/CD00003900.pdf/files/CD00003900.pdf/jcr:content/translations/en.CD00003900.pdf