I am making a battery powered project which involves bi-directional motor control. However motor needs to turn rarely (about 10-20 seconds in 24 hour period). I am using L298 motor driver. However the quiescent current is in mA range. To reduce current consumption, I am planning to use a mosfet switch as shown in the figure below:

VM = 9 V

VCC = 4.5 V or 6 V (I will decide after a little experiment)

Motor current consumption < 1 A

H Bridge with mosfet switch

Whenever I need to use the motor, I will turn the mosfet ON and keep it OFF while the motor is not in use. (I am using logic level mosfet.) The quiescent current of mosfet is in uA range and that's how I am planning to save a lot of battery power.

Will it work?

Any suggestions/improvements are welcome.

  • 1
    \$\begingroup\$ What happens if you just pull the ENA low? \$\endgroup\$ – jippie Jun 21 '15 at 17:56

I suggest using high-side switches rather than a low-side switch.

Edit: One high side switch for each power supply.

Something like this: (Edit: x2)

enter image description here

It needs a base resistor for the BJT or use a logic-level MOSFET. R1 could be something like 10K and the base resistor 20K or so. The p-channel MOSFET should be logic level for your conditions. You can find dual p/n channel units in an SO8 that can handle some amperes.

The problem with switching the ground connection (low side switch) is that there are two power supplies on the chip and the inputs will end up biased at some voltage above ground, which may draw unnecessary current and/or be bad for your micro.

You still have to bring the outputs of your micro low or you will drive unnecessary current into the L298 inputs.

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  • \$\begingroup\$ But this would require two mosfets to switch off both voltages, right? How about the leakage current through transistor? (I am not sure which parameter to look in the datasheet for quiescent current.) \$\endgroup\$ – Whiskeyjack Jun 21 '15 at 17:00
  • \$\begingroup\$ Yes, one high side switch for each power supply. The quiescent currents are quite high. \$\endgroup\$ – Spehro Pefhany Jun 21 '15 at 17:03
  • \$\begingroup\$ So, high quiescent current will beat the purpose of the switch, right? \$\endgroup\$ – Whiskeyjack Jun 21 '15 at 17:04
  • \$\begingroup\$ Yes, you want to have both supply pins go low (and all inputs). \$\endgroup\$ – Spehro Pefhany Jun 21 '15 at 17:06
  • \$\begingroup\$ Not sure if the two of you are typing about the same quiescent current. In OFF state the current in the BJT is 0, only in ON state there is current flow, but I understood from OP that that is for limited periods only. @Whiskeyjack \$\endgroup\$ – jippie Jun 21 '15 at 18:02

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