Electronics > Projects, Designs, and Technical Stuff
Circuit for MosFets in parallel for extra current capacity.(Solved)
<< < (5/10) > >>
Jim-0000:

--- Quote from: spec on December 30, 2018, 10:31:26 am ---
Am I right is saying that the MOSFETs will be used to control the speed of an electric motor which spins the propeller in a model aircraft which flies.....................
--- End quote ---

Spec,
No, that is the function of the ESC (Electronic Speed Controller).
This proposed MosFet switch is to turn the power from the 14.4 volt LiPo battery to the ESC. It is basically a safety measure. Most electric powered models of this category are simply plugged in to the battery (to the ESC as described above) to "switch them on". The danger is if the throttle stick is moved accidentally while the propeller is in near someone, it could cause and injury. The carbon fiber folding propeller on have on my almost built big glider would be like a pair of rotating scimitars.


--- Quote ---How big is the model aircraft?..........
--- End quote ---
This one is 3.8 mtr wing span. Not completed yet, but it has been given a CG test launch with a temporary fuselage.
Full disclosure build thread here:  https://www.rcgroups.com/forums/showthread.php?2787059-4-metre-span-built-up-thermal-plank-build-thread
And the thread that inspired me to investigate a MosFet based switch for my application (60 amps max) is here:
https://www.rcgroups.com/forums/showthread.php?3016539-High-Power-MosFet

--- Quote ---Will pulse width modulation be used to control the speed of the electric motor? ...........................
--- End quote ---
The ESC generates the PWM to control the brushless motor speed.

--- Quote ---What is the construction of the model aircraft..........
--- End quote ---

Please see all construction details and pictures on the build thread......linked above.
......................

--- Quote ---A picture of the model aircraft would be great........
--- End quote ---

Lots of pictures in the thread linked to above.


--- Quote ---Once I get sufficient information about your application, I will do an outline circuit which we can discuss if you like.

--- End quote ---

I much appreciate your assistance. I have a growing feeling that I am out of my depth here. If I miss answering anything you or someone else asked, please be assured it was only due to some degree of overwhelm and not intentional rudeness.
Jim-0000:

--- Quote from: nick_d on December 30, 2018, 10:27:08 am ---.....................
Note the ESC might have the gate driver built in. Check it.............
--- End quote ---

Nick,
Not applicable. This planned MosFet device will be to act as the switch that supplies power to the ESC. Not the other way around.


--- Quote ---Now for my suggestion, the "poor man's gate driver" and that is the 74AC logic family. The thing is though, you would need to have logic-level power MOSFETs, which require a gate voltage of only 5V to turn on, not the 12V as calculated above. I know you already have the traditional (not logic-level) MOSFETs in stock, but if the choice is to order a gate driver or a new MOSFET then the logic-level approach may be attractive. You could get a 74AC541 octal buffer and put 2 of those buffers in parallel to drive each of your 4 gates. No gate resistors required, and each gate driven separately.

cheers, Nick

--- End quote ---

Thanks again Nick. I will do some reading up on the "poor mans gate driver" that you nominate above.
spec:

--- Quote from: Jim-0000 on December 30, 2018, 11:49:37 am ---
--- Quote from: spec on December 30, 2018, 10:31:26 am ---
Am I right is saying that the MOSFETs will be used to control the speed of an electric motor which spins the propeller in a model aircraft which flies.....................
--- End quote ---

Spec,
No, that is the function of the ESC (Electronic Speed Controller).
This proposed MosFet switch is to turn the power from the 14.4 volt LiPo battery to the ESC. It is basically a safety measure. Most electric powered models of this category are simply plugged in to the battery (to the ESC as described above) to "switch them on". The danger is if the throttle stick is moved accidentally while the propeller is in near someone, it could cause and injury. The carbon fiber folding propeller on have on my almost built big glider would be like a pair of rotating scimitars.


--- Quote ---How big is the model aircraft?..........
--- End quote ---
This one is 3.8 mtr wing span. Not completed yet, but it has been given a CG test launch with a temporary fuselage.
Full disclosure build thread here:  https://www.rcgroups.com/forums/showthread.php?2787059-4-metre-span-built-up-thermal-plank-build-thread
And the thread that inspired me to investigate a MosFet based switch for my application (60 amps max) is here:
https://www.rcgroups.com/forums/showthread.php?3016539-High-Power-MosFet

--- Quote ---Will pulse width modulation be used to control the speed of the electric motor? ...........................
--- End quote ---
The ESC generates the PWM to control the brushless motor speed.

--- Quote ---What is the construction of the model aircraft..........
--- End quote ---

Please see all construction details and pictures on the build thread......linked above.
......................

--- Quote ---A picture of the model aircraft would be great........
--- End quote ---

Lots of pictures in the thread linked to above.


--- Quote ---Once I get sufficient information about your application, I will do an outline circuit which we can discuss if you like.

--- End quote ---

I much appreciate your assistance. I have a growing feeling that I am out of my depth here. If I miss answering anything you or someone else asked, please be assured it was only due to some degree of overwhelm and not intentional rudeness.

--- End quote ---

No worries.

Thanks again for the information. That has cleared up and simplified the situation a lot.

There is only one remaining area to be resolved now and that is the high side low side issue, but I am preparing a post for discussion which should enable us to resolve that issue. :)
Jim-0000:
I will attach a picture of a smaller rating Mosfet switch I have made to fit to another type of aircraft. This plane will be internal combustion engine powered, but will of course have radio control. The radio receivers and servos require 6 volts in this application and I have chosen to use an electronic switch instead of a common mechanical one for reliability reasons.
I will also fit this type of switch to my unpowered slope soaring gliders. Some of the higher performance slopers use high power demand servos, so a good reliable supply is essential.
This design is by Vollradth and was posted in the link above.

spec:
+ Jim-0000

Attached is a schematic showing the three switch architectures, mentioned previously. As you can see High Side Switch PMOSFET (HSSP) is the simplest and the best from a functional point of view, but obviously it does not use your FQP50N06 NMOSFETs. Also PMOSFETs do not quite have the same performance as NMOSFETs, but that is unlikely to be a problem (I haven't checked though).

Low Side Switch NMOSFET (LSSN) is also simple and would be the one to go for, in you want to use your FQP50N06 NMOSFETs, provided the ESC was happy feeding an open circuit (a resistor from the ESC output to 0V may be required).

High Side Switch NMOSFET (HSSN) is as functionally good as HSSP, and could use your FQP50N06 NMOSFETs, but with the complication of requiring a high side NMOSFET driver chip.

If you would like to consider these switch architectures and let us know which one you favor, I will knock out an appropriate schematic. For HSSP and LSSN though, the circuits shown are pretty much what the final circuit would be, except that the paralleled MOSFETs (if required) are not shown.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod