Good Evening.
I have constructed several H-Bridge (high-low) power switches before to control large DC motors in my robotics projects. The key downside to such simple bridges (featuring a high and low side MOSFET and a high side inverting NPN as a driver) is the speed at which I can drive them. I use relatively low speed PWM switching, which makes my motors noisy and ringy to the human ear. I am attempting to redesign my driver setup so that I can drive the FETS much faster (above 20khz) and get quieter motor operation.
Parts:
High Side P-Channel MOSFET: AOD403
Low Side N-Channel MOSFET: IRLR8726
( I know the AOD403 FET is obsolete, but it is super cheap and has a nice current rating. I will replace it eventually )
I use a C1815 as my high-side driver NPN.
I have attempted to create a NEW design capable of faster operation...
Proposed Design:
By carefully selecting the base resistors of the NPNs, I can limit the CE current to within their ratings.
The current will still be MUCH higher than the 40mA my Microcontroller can supply, charging the gate capacitance faster and thus allowing for higher PWM frequencies. I added the 12v zener diode to prevent the High Side gate voltage from exceeding ratings. I plan on operating motors between 12 and 25 volts. Note that both Power MOSFETS are logic level.
Is there anything wrong with the above circuit? I have never seen NPNs used to pull up a gate that has been pulled down, but with fast switching I would need small pull up/down resistance, and an inverting setup would require dissipating power over this small resistor when idle. I would like to avoid gate driver ICs if possible...
I have constructed several H-Bridge (high-low) power switches before to control large DC motors in my robotics projects. The key downside to such simple bridges (featuring a high and low side MOSFET and a high side inverting NPN as a driver) is the speed at which I can drive them. I use relatively low speed PWM switching, which makes my motors noisy and ringy to the human ear. I am attempting to redesign my driver setup so that I can drive the FETS much faster (above 20khz) and get quieter motor operation.
Parts:
High Side P-Channel MOSFET: AOD403
Low Side N-Channel MOSFET: IRLR8726
( I know the AOD403 FET is obsolete, but it is super cheap and has a nice current rating. I will replace it eventually )
I use a C1815 as my high-side driver NPN.
I have attempted to create a NEW design capable of faster operation...
Proposed Design:
By carefully selecting the base resistors of the NPNs, I can limit the CE current to within their ratings.
The current will still be MUCH higher than the 40mA my Microcontroller can supply, charging the gate capacitance faster and thus allowing for higher PWM frequencies. I added the 12v zener diode to prevent the High Side gate voltage from exceeding ratings. I plan on operating motors between 12 and 25 volts. Note that both Power MOSFETS are logic level.
Is there anything wrong with the above circuit? I have never seen NPNs used to pull up a gate that has been pulled down, but with fast switching I would need small pull up/down resistance, and an inverting setup would require dissipating power over this small resistor when idle. I would like to avoid gate driver ICs if possible...