Hi all,
I am designing a DC motor controller for brushed motors which needs to have regenerative braking. The braking is achieved by the low side mosfet running at a certain duty cycle and the high side mosfet being off completely with the voltage pulses from the motor being conducted back into the battery through its body diode. This isn't a 300v controller, it is designed for a maximum of 50v.
I am currently going with this design above but that prevents me from having a 100 percent duty cycle on the high side mosfet due to the bootstrap capacitor (C1) discharging. I would need to occasionally pulse the low side mosfet to allow the bootstrap capacitor to charge. Is there a better way to design this so I can have 100 percent duty cycle on the high side? The circuit below for the high side has been explored but it doesn't switch fast enough for this application. I will need about 10KHz switching.
Please add the motor and battery to your circuit diagram and show the way back into the battery.
I'm not sure what you mean by 100% here. Permanent current can be achieved without any circuitry, by direct connection of the load to the power source.
Right, you built a constant current source depending on V1 - Vbe on R1, delivering about 25mA for turning M1 on. Turning off is yet worse with a top current of 1mA limited by R3. Check the gate voltage of M1 using a scope to find out how slowly the gate voltage is changing. Then you may understand what bipolar MOSFET drivers are made for.
It is not practical to just connect the motor directly to the battery while riding my bike and then connecting it back to the controller when I want less than 100 percent throttle. The motor is to be connected between out and GND when you look at the top circuit.
That's right and in this loop is no battery to be loaded.
Yes, there is, via the body diode of the top mosfet. If you short the motor briefly using the bottom fet, as soon as that short is removed, there is a voltage pulse higher than the battery voltage which is rectified through the body diode and back into the power source. Short the motor out at 10khz, and you have constant regenerative braking. It's like how a dc boost converter works. I am just looking for a way for the high side mosfet to be able to run at 100 percent duty cycle which will be needed when full power is called for. if someone with an understanding of H bridge design can chip in and share some knowledge.
Please understand that 100% duty cycle means that the MOSFET is ON all the time, no switching. Switching times are of interest as soon as you want a less than 100% duty cycle.
Shorting the low side MOSFET at the same time produces a short burning both transistors.
Please add the motor to your circuit diagram so that we can discuss how it's different from a boost converter.
Until now you only show a half H bridge. I tried to point out in my #2 why your simplified circuit is switching slowly.
