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How to Make a Transistor H-Bridge

An H-bridge is an electrical circuit that allows you to apply a voltage across a load in either direction. You can build H-bridges using manual switches or using electrically controlled switches such as transistors. You can use H-bridges to control the speed and direction of electric motors. They are often found in robot arms or in any application that requires fine multidirectional control of electric motors.

Things You'll Need

Ground plate
2 standard breadboards
2 2N2222 NPN BJT transistors
2 2N2907 PNP BJT transistors
1 electric motor
Short electric wires
3 15-volt variable power supplies
power leads
4 1 kilo-ohm resistors

Instructions

- 1
  Clip the two standard breadboards together and place them on the ground plate. Place the two PNP transistors next to each other but on different breadboards. Place the two NPN transistors next to each other but on different breadboards.
- 2
  Place the motor so one of its terminals rests in an unoccupied slot in one of the breadboards and the other terminal rests in an unoccupied slot in the other breadboard. Connect the collector terminal of the PNP transistor on each breadboard to the motor terminal on the same breadboard using short wires. Connect the collector terminal of the NPN transistor on each breadboard to the motor terminal on the same breadboard using short wires.
- 3
  Connect the emitter terminals of the two PNP transistors to each other using short wires. Connect the emitter terminals of the two NPN transistors to each other using short wires.
- 4
  Insert one end of one of the power leads into the positive terminal of one power supply and attach the other end of this lead to the emitter terminal of one of the PNP transistors. Insert one end of one of the power leads into the ground terminal of the power supply and attach the other end of this lead to the emitter terminal of one of the NPN transistors. Set the power supply to 2 volts. Turn on the power supply.
- 5
  Attach one terminal of each of the 1 kilo-ohm resistors to the base terminal of each of the transistors. Attach the other terminals of the two resistors on the left breadboard to the side-line of the left breadboard. Attach the other terminals of the two resistors on the right breadboard to the side-line of the right breadboard.
- 6
  Insert one end of one of the power leads into another power supply and attach the other end of the power lead to the side-line of the left breadboard. Insert one end of one of the power leads into the third power supply and attach the other end of the power lead to the side-line of the right breadboard.
- 7
  Set both power supplies to 0.5 volts. If one of the two 0.5-volt power supplies is on, the motor will rotate in one direction. If the other of the two 0.5-volt power supplies is on and the other is off, the motor will rotate in the opposite direction. If both 0.5-volt power supplies are on, the motor will stop. If both 0.5-volt power supplies are off the motor will stop.

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