Ready, set, amplify

Once some of these decisions have been made, there are two major design approaches for motion amplifiers. The first utilizes all-in-one low power amplifier ICs, while the other utilizes discrete components such as pre-drivers, MOSFETs or IGBTs and other circuitry. All-in-one amplifier ICs integrate PWM signal input, current control, a charge pump and switched output voltage drive into a single IC unit. Although incredibly convenient, they top out at about 36 volts and 4 amps of output, often less — depending on the application. If your application exceeds that, or if you are looking for higher performance and more control over the design, you will likely be using the discrete approach to assemble the amplifier.

Until recently, designing a discrete component amplifier from scratch, particularly one with current control and high efficiency MOSFET switchers, was a complex undertaking. But in the last year a new type of motion control IC has been developed by several companies — including International Rectifier and Performance Motion Devices, Inc. (PMD). Known as intelligent motor controllers (IMC), these devices are designed to interface with external switchers such as MOSFETs or IGBTs, while internalizing functions such as current control, PWM generation, shoot-through protection, and more.

Figure 4 shows a block diagram of a typical intelligent amplifier IC. It can be programmed to perform commutation, torque control and velocity control. It can communicate via a serial port to a microprocessor, or can accept a direct SPI data stream for autonomous operation.

Future improvements for intelligent amplifier ICs may include more power efficient commutation techniques and other features designed to work with high power, high efficiency motor applications. Power efficiency in traditional positioning motion control is not usually a primary concern, but for ancillary markets such as white goods, electric vehicles, and industrial applications (such as pumps, compressors and A/C units) it is rapidly becoming very important.