Designs based on dc drives excel in an array of industries. That’s because some applications benefit from dc drives and the distinct characteristics they offer—including simple speed control, cost-effective integration, and long life. Common dc-drive applications include the movement of axes on wire-drawing machinery, hoists and elevators, paper-web handing, extruding applications, spindle drives, and material handling.
Machines that use dc drives paired with brush motors for speed control incorporate a silicon controlled rectifier (SCR) for power conversion. This SCR or thyristor converts ac power input to adjustable-voltage output that goes to the motor armature. SCRs provide controllable power output by phase angle control, so called because the firing angle synchronizes with the ac source’s phase rotation.
Brushless dc motors paired with dc drives offer an alternative to conventional dc drives and ac inverters, marketed as dc-drive replacements. Of course, brushless dc motors have windings on the stator and permanent magnets on the rotor; rotor-position feedback from an encoder or Hall-effect sensors send speed information back to a controller as a way to facilitate adjustment of electronic commutation on the fly.
The advantages of dc drives include the ones just mentioned and wide speed ranges, good speed regulation, and starting and accelerating torques that exceed rated torque by 400% or more. Matching a dc drive to a given application ultimately depends on the application’s starting torque. Other relevant factors include input power factor, the need for dynamic braking, speed regulation, range, and need for high speed, and conduciveness to energy regeneration.
Drives for dc motors also come in chip-level packaging for placement on circuit boards. For example, two new motor drivers from Texas Instruments (TI) are specifically designed for automotive applications such as driving dc motors in various systems such as fans and pumps. They’re part of a growing trend toward smaller, more compact dc motor drivers designed to accommodate the growing number of applications for small dc motors.
The motor drivers support high-performance powertrain applications. The DRV8305-Q1, an integrated three-phase brushless DC gate driver, and the UCC27211A-Q1, a high-current half-bridge gate driver, improve system performance and provide design flexibility to meet a diverse range of automotive system requirements.
For powertrain applications such as transmission pumps or engine cooling fans, the DRV8305-Q1 features a smart gate-drive architecture with programmable slew-rate control that allows easy optimization. It operates down to 4.4 V to support start-stop functionality, which lets car manufacturers meet strict fuel efficiency and carbon-dioxide emission standards. Also, an integrated 3.3-V or 5-V linear regulator, three current-sense amplifiers and smart gate-drive architecture reduce board size and eliminate up to 20 external components. Advanced on-chip protection with detailed fault diagnostics guard against overtemperature, undervoltage lockout, MOSFET shoot-through and overcurrent events.
The 100-V UCC27211A-Q1 half-bridge gate driver supports both brushed and brushless dc motor applications. The half-bridge design means gate drivers can be placed closer to the MOSFETs, minimizing parasitic inductances and simplifying overall board layout. It features a fast propagation delay of 15 nsec, rise and fall times of 7 nsec and a 4-A peak gate drive. A negative voltage rating of -12 V also protects the driver from potentially damaging voltage spikes.
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