STMicroelectronics First dual operational amplifier for rotary transformers in electric vehicles

The TSB582 is ST's first high-voltage, high-current dual operational amplifier in a compact package (SO8 with bare pads and DFN8 with bare pads and wettable surfaces). First consider using it for rotary transformers in electric vehicles, or other applications with high-power AC motors or brushless DC motors (which convert mechanical motion into electrical data) to determine motor position and improve efficiency. In addition, the size of the op amp and its pin compatibility with other op amps make it an excellent general purpose device for piezoelectric actuators.

Why are rotary transformers so important in electric vehicles?

Precision of motor control algorithm

 Electric vehicles must carefully adjust the current sent to each motor to provide the desired performance. For example, when an electric vehicle turns left, the motor control algorithm must quickly and accurately drive the IGBT on the left and right motors to generate the appropriate torque and ensure a smooth driving experience. Similarly, the accelerator must accelerate immediately when pressed, and knowing the exact position of the wheels will ensure that the driver can easily control the car. In short, the precise position of the wheel is crucial to the motor control algorithm. So why do engineers tend to use rotary transformers instead of encoders?

 A rotating transformer uses a primary coil in the rotor. In addition to this reference coil, there are two secondary windings in the stator that are positioned 90° from each other. One of the windings is called a sinusoidal winding because the system reports its sinusoidal amplitude, while the other is a cosine winding. In simple terms, alternating current passes through the primary coil, and as it moves, its electromagnetic field excites the secondary winding. By measuring the current change in each winding, the sine and cosine functions can be obtained. The program can then apply the arctangent function through the sine and cosine values to obtain the precise Angle of the rotor.

 Rotary transformers and electric vehicles are popularized

 From the basic overview of the inside of the rotary transformer, you can see that this sensor is fast and stable. Because the mechanism and electronics are simple, there is no need to worry about difficult failures. This explains why manufacturers favor rotary transformers over encoders. The high temperature resistance of rotary transformers allows automakers to place rotary transformers closer to the motor without worrying about operating conditions. In this way, the manufacturer's requirements for the size of the rotary transformer are also met. By reducing design and components, teams can create products that are more powerful and easier to use. Therefore, further improvements to rotary transformers can continue to reduce costs and make electric vehicles easier to purchase.

Why is TSB582 so popular in rotary transformers?

With an understanding of how rotary transformers work, it's easy to understand why engineers are used to using two op amPs on primary coils. However, the TSB582 offers two channels, allowing designers to use only one high-current op amp, cutting the power stage in half and reducing material costs. In addition, designers can use two channels in parallel to double the output current to 400 mA to support industrial applications using servo motors or robotic arms. In addition, the TSB582 is also pin-compatible with other operational amplifiers, greatly increasing its own utility. A single qualification can be used for multiple designs, thereby reducing the cost of research and development.

Harsh condition protection

Another important advantage of rotary transformers is their durability. The TSB582 is equipped with output current limiter and short circuit and overtemperature protection to help cope with harsher conditions. For example, for thermal safety functions, the device automatically turns off the output power stage to cool it down. Once the temperature drops below a certain level, it will be restarted. Engineers don't have to worry about adding safety measures, just taking advantage of them when planning for extreme conditions. The ST data book even contains PCB layout recommendations and application examples to help designers with their work.