08-16-2017, 09:51 PM
Common DC gear head motors need current over 250mA. There are many integrated circuits like ATmega16 Microcontroller, 555 IC timer. But, the IC series 74 can not supply this amount of current. When the motor is connected directly to the o / p of the above integrated circuits, they may be damaged. To overcome this problem, an engine control circuit is required, which can act as a bridge between the previous motors and the ICs (integrated circuits). There are several ways to make H bridge motor control circuit such as using transistor, relay and using L293D / L298.
H-Bridge Circuit
A H-bridge is an electronic circuit that allows a voltage to be applied across a load in any direction. H-bridge circuits are often used in robotics and many other applications to allow DC motors to operate forward and backward. These motor control circuits are mainly used in different converters like DC-DC, DC-AC, AC-AC converters and many other types of electronic power converters. Specifically, a bipolar stepper motor is always driven by a motor controller having two bridges in H.
An H-bridge is manufactured with four switches such as S1, S2, S3 and S4. When the switches S1 and S4 are closed, a + ve voltage will be applied through the motor. By opening the switches S1 and S4 and closing the switches S2 and S3, this voltage is reversed, allowing reverse operation of the motor.
Generally, the excitation circuit of the H-bridge motor is used to reverse the motor direction and also to brake the motor. When the motor stops suddenly, since the motor terminals are shorted. Or let the engine run freely until it stops, when the engine comes off the circuit. The following table shows the different operations with the four switches corresponding to the previous circuit.