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I want to control a 4V motor to rotate both directions which draws 100mA and I was looking at the H-bridge schematics. The tutorial says that you should place NPN transistors at the bottom if you need >5V Power to the motor, which i dont need. This H-bridge also requires at least two inputs to switch direction. I also do not need to turn the motor off. It will run either or one direction, or the other.

I was wondering if I could put the NPN transistor at the top, so that I can control the motor with only one I/O pin (simplified schematic):

schematic

simulate this circuit – Schematic created using CircuitLab

Since I don't need >5V power for the motor, I don't need to put my NPN transistors at the bottom. Using this schematic I can also control the direction of the motor with only one I/O, without more external components.

Of course, the complete schematic will also include a resistor to limit the Base current and the fly back diodes (fly back diodes and Base resistor added):

schematic

simulate this circuit

When I/O is 5V, both NPN transistors turn on.

When I/O is 0V, both PNP transistors turn on.

Do you think this will work? I have not seen any tutorial/schematic with this H-bridge configuration.

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    \$\begingroup\$ This can easily be simulated in LTSpice. Or any of the additional free simulators. I do wonder if your MCU will be able to drive two transistors into saturation though. Simulation and datasheet inspection can answer that though. \$\endgroup\$
    – Aaron
    Commented Mar 3, 2021 at 16:08
  • \$\begingroup\$ Hm you are right! i should start using that LTSpice. \$\endgroup\$ Commented Mar 3, 2021 at 16:09
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    \$\begingroup\$ no good. the common emitter pair on the right side turn each other on. \$\endgroup\$
    – Pete W
    Commented Mar 3, 2021 at 16:10
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    \$\begingroup\$ @PeteW Right, the right side pair is just 2 diode junctions right across the supply, and the left side pair are emitter followers which can only pull down to a diode drop above ground or up to the base drive voltage minus a diode drop. The left side of the bridge could kind of work if the power dissipation in the transistors is OK. \$\endgroup\$
    – John D
    Commented Mar 3, 2021 at 16:16

1 Answer 1

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As @Aaron stated, I should simulate this in LTspice.

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