If your H-bridge and the Arduino are running from the same +5V supply, then you can switch either the high side or the low side of the H-bridge. You can use either a logic-level P-channel mosfet to switch the high side, or a logic-level N-channel mosfet to switch the low side. The P-channel mosfet needs a pullup resistor between gate and +5V to hold it off while the system is powering up; the N-channel mosfet needs a pulldown resistor to ground for the same reason. In both cases, when the mosfet is off, there is no voltage across the resistor, so no associated current drain.
If your H-bridge uses a different +5V (or higher) power supply from the one powering the Arduino, then you must use high-side switching, with a P-channel mosfet and an NPN BJT or similar to level-shift the mosfet gate drive. The usual level shifting circuit consumes no power when the mosfet is off.
I suggest you include 1K resistors between INA, INB and the corresponding Arduino pins, to protect the chips in the event of you getting the sequence wrong.
Here is my suggested operating sequence:
- Low side switching with N-channel mosfet (output pin high to turn mosfet on)
Initialise:
digitalWrite LOW to mosfet control
mosfet control pinMode to OUTPUT
digitalWrite HIGH to INA, INB
INA, INB pinMode to OUTPUT (both will be set HIGH because of the previous command)
Power up:
INA, INB should both already be HIGH
Mosfet control HIGH to enable power to H-bridge
Power down:
INA, INB HIGH
Mosfet control LOW to power down H-bridge
- High side switching, direct connection to P-channel mosfet (output pin low to turn mosfet on)
Initialise:
digitalWrite HIGH to mosfet control
mosfet control pinMode to OUTPUT
DigitalWrite LOW to INA, INB
INA, INB pinMode to OUTPUT
Power up:
INA, INB should already be LOW
Mosfet control LOW
Power down:
INA, INB LOW
Mosfet control HIGH.
- High side switching with level shift: as (2) but reverse mosfet control pin HIGH/LOW.