The conventional universal motors used in many kitchen and garage appliances, power tools and other small household appliances typically lack accurate speed control. Basically, the motor is either in the on or off state which, for some applications, is adequate. However, introducing accurate and variable speed control through the implementation of a digital power management system offers numerous and significant benefits, including:
- Lower power consumption
- Increased safety
- An increase in the appliance life cycle
- Greater ease of use
- Improved operating control
- Minimized risk of circuit-tripping energy surges that can occur when an appliance is switched on
Historically, the primary obstacle to implementing what we term 'intelligent motor control' in many consumer appliances has been the costs associated with doing so. In this paper we will discuss a new, cost-effective variable-speed universal motor control solution developed by design engineers at ZiLOG, and how the implementation of this solution makes use of innovative on-chip integrated digital and advanced analog hardware blocks to enable speed control and fault-condition shut down capabilities with a minimal set of external components and firmware.
Overcoming cost and complexity
One widely-held 'traditional' view from within the electronics industry is that the components required to build systems that enable direct, accurate and variable speed control were simply too expensive to be used in price-sensitive consumer appliances. The thinking was basically that it's far better to keep costs low and trade off the benefits of intelligent motor control than the develop and implement such a control system, only to have to increase the end unit retail price, making the product less commercially attractive. In addition, motor control applications posed a unique set of engineering challenges due to problems such as fast over-current detection and fault control, system reliability and efficiency.
Due to the need for fast and accurate closed-loop control, as well as the number and cost of supporting components required to execute intelligent motor control through digital power management, these controller applications have raised the bar in terms of what is expected from an MCU, requiring the delivery of optimum performance, as well as a rich set of integrated, advanced features which simplify the implementation of closed-loop control design for universal motor control applications.
The last few years have seen the emergence of microcontrollers (MCUs) dedicated to motor control, devices that integrate 8-bit computational engines, analog to digital converters (ADCs), comparators, counters, timers and other circuits to control motor speeds to meet the power requirements of the load. The battle facing MCU manufacturers now is how to best integrate the correct external components and functionality and still keep costs to the customer attractive.