Can I add an additional stage of mosfets to increase current capacity of a speed controller? Whatwou

I build electric bicycles. they all use brushless motors, and all the controllers are fairly similar.

There are various current capacity controllers available, but I want to know if I can use the output of a small controller to drive an additional bank of mosfets, thereby making it a large current controller. Can this be done or do I need to use the signal that drives the original mosfets?

The goal is being able to increase the power of a bike with an add on box to the controller.
If this can be done, What other circuitry, besides the mosfets themselves would be required?
Here is a schematic of a speed controller for reference.

Shepherd, that MC33035 looks like a nice little IC.  Looking at the data sheet, the outputs are push/pull bipolar transistors and they give rise times in the ns for a load of 47pf and 1K.  Elsewhere they specify sink and source currents of 25 or 50 mA.So given that this is for driving a bicycle motor (a) you wouldn't need a huge amount of power and (b) you wouldn't want very high motor speeds, I reckon you could just increase the beefiness of your output transistors.  There is also a current limit sensor circuit at bottom right.  This is a comparator with a threshold voltage of around 100 mV.  You are using a 50 milliohm resistor which will switch the comparator on at 2A.  You'd need to reduce this value to allow bigger motor currents (0.01 ohms would increase this to 10A).You could also approach ON Semiconductor support for assistance, especially for commercial applications where they will be selling ICs, they should be helpful.If your controllers are sealed and it is impossible or impractical to modify them then yes you should be able to use your controller as a driver.  But if possible you should still use a smaller current sense resistor - you could just connect it to ground and TP2 on your diagram, if TP2 is accessible to you. If you are looking at high volumes then it might be worth your while getting some custom boards made.Good luck with it!

Hi Shepherd-Thanks for providing a schematic.  That makes the answer a lot easier.Yes- you can do this, but probably not as an external box.  You'll need to disable the existing output stage and attach wires to a new circuit board containing drivers and bigger MOSFETS.I would start by removing the 1K resistors and 470 ohm resistors going to the existing MOSFET gates. Now add a three dual channel non-inverting MOSFET drivers, like the Microchip MCP14E4.  Connect the inputs to the point where you removed the resistors, and connect the outputs to the bigger MOSFETS. Remember that the top three MOSFETS must be P-channel, and the bottom ones must be N-channel. It would be good practice to connect a 10K ohm pull-down resistor between each of the driver inputs and ground.  This will help insure that the upper and lower MOSFETS of each pair can never both be on at the same time (that would be BAD).This leaves one remaining issue- the original circuit has a current monitoring feature. To make sure this still works you will need to provide a new lower-value shunt resistor between the source pins of the lower three MOSFETS and ground. It will need to be connected back to the point labeled TP2 on the schematic after removing the original .05 ohm resistor.I know this may sound very intimidating, but if you want to pursue it we will be happy to help walk you through it.-Rick

David,Thank you for providing such a thorough and detailed answer to my question!I really appreciate the effort you put into this, and I think you answered this to the point where I have no more questions.

Rick,I really have the same thing to say to you as I told David.Thank you for providing such a thorough and detailed answer to my question!I really appreciate the effort you put into this, and I think you answered this to the point where I have no more questions.

Now add a three dual channel non-inverting MOSFET drivers, like the Microchip MCP14E4.  Connect the inputs to the point where you removed the resistors, and connect the outputs to the bigger MOSFETS.

Cologne- Your post was copied in its entirety from my post above.  Not good.  Don't do that again.