Current Sensing in an H-Bridge

Current Sensing in an H-Bridge

The semiconductor industry has always looked for improvements in creating technology that has the ability to enable higher power efficiency systems. One such circuit is an H-bridge. An H-bridge is a simple circuit consisting of 4 FET transistors connected between the load. It is often used when the direction of the current is required to be controlled and managed from the supply to the load. If the load load is highly inductive, the energy stored in the load can also be discharged safely to ground by controlling the h-bridge. H-bridge circuits are commonly used in motor control, DC-DC converters, audio sub systems and LED lighting control.

H-Bridges consisting of silicon FET transistors often achieve >95% efficiency, while GaN FET transistors can allow for efficiencies beyond 99%. A higher efficiency h- bridge combined with current sense amplifiers to monitor, manage, and control the load currents leading to improvement in safety and overall improvements in the efficiency of an end equipment.

The figure describes common locations to measure current in an H-bridge: high-side, in-line and low-side. As motors are highly inductive, the PWM output tends to overshoot during low to high transitions and undershoot during high to low transition. The characteristics of overshoot and undershoot of an amplifier are important in selecting a correct component. A current sense amplifier that can sustain overshoot and undershoot can survive the harsh requirements of an inductive system and provide valuable current information that can detect abnormalities of the motor which can lead to early failure.

Sources: Texas Instruments

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