Hi,
The attached image is a schematic on the IRS2001IRS2001
from what i can understand Vcc is is the low input, let's say its a 5v logic and the high voltage lets say 12v is connected to the source of the HI mosfet, when the gate is powered isn't the capacitor between the Vs and Vb reversed? Vs will see 12v and Vb should see 5v minus the diode value.
could someone please help explain this schematic to me?
Thanks,
Vcc should be 12V and powers both drivers, Hin and Lin are logic inputs that are compatible
with 3V or 5V logic.
The diode and capacitor are the charge pump/bootstrap for the high side driver, the diode must be a
fast recovery or schottky diode. So long as you PWM the inputs at a sensible rate the
high side driver gets its own 12V supply that rides with the high MOSFET source and topped
up every time in the PWM cycle when the low MOSFET is on from Vcc.
If you don't understand charge pumps and bootstrapped voltage supplues I suggest reading up
about them.
All you need to know is Vcc is 12V with good decoupling, the bootstrap capacitor should be 10 times
or more than the total MOSFET gate capacitance, and that you must drive with PWM or else
park the inputs Lin high and Hin low. Leaving Hin high and Lin low for more than a few milliseconds
causes the bootstrapped supply for the high side to droop and the top driver will cut out.
The supply to the MOSFETs themselves can be anything from <1V to 200V, the circuit is completely
unaffected by the output voltage and will work just the same because the high side driver just rides
with the output. The clever bit of the chip is the circuit that level shifts Hin from logic level to anything
upto 200V
Hi Mark,
Thanks for your reply, although i understood what you wrote it does sound a little wired,
what im trying to understand is while your pwming the Hi and Low sides the engine is moving from turning to braking as you say i cant leave the high side on for more than a few milliseconds (i assume this has to do with the capacitor depletion) how could you drive a motor at a 100% duty cycle for its peak performance given a 12v source and 12v capable engine?
You drive it at 98% maximum or so, and all's fine.
Some driver chips have a separate independent charge-pump circuit so they can work
with 100% drive, such as the HIP4081A.
Thanks Mark,
As always the best source around for information 
I would love to understand this issue a little better.
MarkT:
You drive it at 98% maximum or so, and all's fine.
Please elaborate on how it is i do that? every time i enable the low side mosfet to charge the capacitor for the high side im shorting the motor, no matter how fast i can do that i don't get how its even close to 98%?
could you please provide example cod / waves / explanation on how to pwm the low and high side to achieve this?
98% duty recycle, ie not quite 100% duty cycle, because that wouldn't charge the capacitor.
This is a switch-mode circuit, where there are switches, capacitors and inductors. The motor
winding itself is the inductor. The fact the motor is "shorted" isn't an issue, the current changes
only slowly in response to the PWM'd voltage, it averages it out. The switching frequency
has to be high enough that this is the case, so some experimentation may be needed, but typical
frequencies used for motor control are 4, 8, 16, 20kHz
Thanks Mark.
Ok, think i got it, so since the frequency is so high the motor don't actually have time to lose it's charge.
So i would have to use the arduino timers in order to play with the frequencies so i can test it out.
Also to make sure i am coding the correct frequencies (timers are a pain in arduino) i would need access to an Oscilloscope?
Its not charge, its the current and magnetic field that doesn't have time to
change much. Inductance resists change in current because the magnetic field
stores energy proportional to current squared - changing the current means
pushing that energy around.
You can check any timer setup code using a frequency counting sketch, just
connect the PWM pin to an interrupt pin if the frequency sketch uses interrupts (there
will be a few such sketches out there I'm sure).
Thanks Mark.
Ok, think i got it, so since the frequency is so high the motor don't actually have time to lose it's charge.
So i would have to use the arduino timers in order to play with the frequencies so i can test it out.
Also to make sure i am coding the correct frequencies (timers are a pain in arduino) i would need access to an Oscilloscope?
If you're using these to make an H-bridge, you will need to make damn sure that you never have both FETs on one side on at the same time. That's called shoot-through, and it's bad. An actual H-bridge driver will have logic to prevent that, this doesn't look like it does.
Some H-bridge drivers have shoot-through prevention, some don't, and the length of dead-time
varies for those that do (some are programmable). As always there is a datasheet and you need
to read it to check all these details.