The bridge H is an electronic circuit that allows the voltage applied to the load in the opposite direction. These circuits are often used in robotics and other applications to allow DC motors to run forward or backward.
Most DC-to-AC converters (power inverters), mostly AC/AC converters, DC-to-DC push-pull converters, most motor controllers, and many other types of power electronics use H bridges. Specifically, bipolar stepper motors almost always driven by a motor controller containing two H bridges.
Video H bridge
General
H bridge is available as an integrated circuit, or it can be built from discrete components.
The term H bridge is derived from a typical graphical representation of the circuit. H bridge is built with four switches (solid-state or mechanical). When the switch S1 and S4 (according to the first drawing) are closed (and S2 and S3 are open), a positive voltage will be applied across the motor. By opening the S1 and S4 switches and closing the S2 and S3 switches, this voltage is reversed, allowing motor backward operation.
Using the above nomenclature, the S1 and S2 switches should not be closed at the same time, as this will cause a short circuit at the input voltage source. The same goes for S3 and S4 switches. This condition is known as a shoot-out.
Maps H bridge
Operation
The H-bridge arrangement is commonly used to reverse the polarity/direction of the motor, but it can also be used to 'brake' the motor, where the motor abruptly stops, because the motor terminal is shortened, or to let the 'free run' motor to stop, effectively disconnected from the circuit. The following table summarizes the operation, with S1-S4 according to the diagram above.
Construction
Relays
One way to build H bridge is to use relay array from relay board.
Double Pole Double Throw (DPDT) relays can generally achieve the same electrical function as the H bridge (considering the usual function of the device). However, semiconductor-based H bridges would be better for relays where smaller physical size, high-speed switching, or low driving voltage (or low driving power) are required, or where unnecessary mechanical parts are used.
Another option is to have a DPDT relay to set the direction of current flow and transistor to enable the current flow. This can extend the life of the relay, since the relays will be diverted when the transistor is off and thus there is no current flow. It also allows the use of PWM switching to control the current level.
N and P channel semiconductors
A solid state H bridge is usually built using opposite polarity devices, such as a bipolar junction PNP (BJT) or a P-channel MOSFET connected to a high-voltage bus and a NPN BJT or N-channel MOSFET connected to a low-voltage bus.
Only N channel semiconductors
The most efficient MOSFET designs use N-channel MOSFETs on the high side and low side because they typically have a third of the ON resistance of the P-channel MOSFET. This requires a more complex design because the gate of the high side MOSFET should be positively driven with respect to the DC supply rail. Many integrated gate driver MOSFET circuits include charge pumps in the device to achieve this.
Alternatively, an active-mode DC-DC power supply modifier can be used to provide an isolated ('float') supply to the gate drive circuit. A multi-output flyback converter is perfect for this application.
Another method for driving a MOSFET-bridge is the use of a special transformer known as GDT (Gate Drive Transformer), which provides an isolated output to drive the upper FET gate. The transformer core is usually a ferrite toroid, with a 1: 1 or 4: 9 winding ratio. However, this method can only be used with high frequency signals. The design of the transformer is also very important, since the leakage of the inductance must be minimized, or cross conduction may occur. The output of the transformer is usually clamped by a Zener diode, because a high voltage spike can destroy the MOSFET gate.
Variant
The common variation of this circuit uses only two transistors on one side of the load, similar to a class AB amplifier. Such a configuration is called a "half bridge". The half bridge is used in some switched-mode power supplies that use synchronous rectifiers and in switching amplifiers. The half-H bridge type is usually abbreviated to "Half-H" to distinguish it from full bridge ("Full-H") H. Another common variation, adding a third 'leg' to the bridge, creating a three-phase inverter. The three phase inverter is the core of any AC motor drive.
The next variation is a half-controlled bridge, where a low-side device on one side of the bridge, and a high-side device on the opposite side of the bridge, each replaced with a diode. This eliminates the shooting failure mode, and is usually used to drive a malignant variable or switch engine or switcher where bi-directional current flow is not required.
Commercially available
There are many commercially available single and dual H-bridge packages, in which the L293x series is among the most common. Some packages, such as the L9110, have a built-in flyback diode for rear EMF protection.
Operating as an inverter
The general use of H bridge is the inverter. This arrangement is sometimes known as a single phase bridge inverter.
H bridge with DC supply will generate square wave voltage wave across load. For a pure inductive load, the current waveform will be a triangular wave, with its peak depending on the inductance, switching frequency, and input voltage.
See also
- Active rectification
- Commutator (electric)
References
External links
- Video tutorial on H-bridge and example of two-way motor speed control circuit
- Theory and Practice of H-Bridge
- Short Theory H-Bridge Operation
- The H-bridge tutorial discusses various driving modes and reuse-EMF
- DC PWM Motor Controller Using MOSFET and H-Bridge IR2110 Driver
- H-Bridges on BEAM Robotics Wiki
- Decrease the formula to estimate the current H-bridge controller (Vex, JAGUAR, Victor). Discuss why some of the H-bridges used in robotics have a non-linear current and velocity response.
Project
- Build a H-bridge controlled motor with a photocell to track light
- H-bridge motor control with 4017 (in Turkish)
- Use HIP4081A for H-bridge control
- Uses the L293D H bridge for DC motor control
- A simple circuit designed around the L293D motor driver driver
Source of the article : Wikipedia
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