Digital technology will govern power control
Digital technology will be the focus for power control in the 1990s. Digital control is nearly twice as efficient as linear control and offers savings in size and weight of end products. Transformers required for linear control are practically eliminated in digitally controlled off-line switchmode supplies.
Digital control of brushless motors is much more efficient than linear control. Integration of a control IC and a MOS power transistor on a single chip, called ‘smart power’, could lead to the development of a complete switchmode power supply on one chip by the end of the decade. High-voltage ICs will bring about major changes in components such as motors, relays and sensors that have remained unchanged for years. The 1990s will see the development of smarter electrical products, such as electrical outlet boxes in homes that can be programmed from a central computer, and household products with built-in temperature sensors to prevent dangerous heat levels.
Power control in the 1990s will see design emphasis shift decidedly from linear to digital technology. One reason is that digital control of power devices is about twice as efficient as linear. Second, digital techniques allow for a tremendous reduction in the size and weight of the end product. By the end of the decade, digital control will dominate–just a few isolated linear applications will remain.
Digital technology impacts power-supply design and load control. For example, the big, heavy step-down transformers required by linear supplies can be virtually eliminated in off-line switchmode supplies under digital control. A 100-W supply that fits into a desktop PC would be impossible to build using linear technology. Beyond switchmode supplies, IC technology can power chips directly from the ac line.
Control of brushless motors is made more efficient by digitally switching the motor voltage on and off rather than varying it linearly. Digital control also can result in a dc-variable stepwise approximation to a sinewave. Varying the power to any kind of load is more efficient than applying a steady ac voltage. Ample savings in system power consumption can be achieved by applying one level of power to actuate a relay or solenoid, and then reducing the power to hold it. With less power, the voltage to the device can be increased above its rating, enabling faster operation. This can increase the productivity of machinery without adding capital investment.
An idea that’s taking hold is the integration of a control IC and MOS power transistor on one chip, a concept now called “smart power.” By the end of the 1990s, smart power will probably lead to a complete switchmode power supply contained in one IC.
At low voltage–up to about 60 V–a smart-power IC is more cost effective than an IC plus a discrete power transistor. A perfect example in bipolar technology is one of the original smart-power devices called a three-terminal regulator.
To operate at higher voltages (200 V and more), you need a mixed process–an MOS output with either a bipolar or CMOS input. Up to now, it wasn’t easy to build these smart-power structures. You need large silicon areas to isolate high- and low-voltage devices and you must use IC processing, which is more expensive than discrete processing. Moreover, you can’t use some of the processing tricks with ICs that can be employed in discrete processing.
At Power Integrations, we’ve developed a high-voltage processing technology that overcomes the aforementioned problems. We can build a high-voltage smart-power IC using the same processing steps that are utilized in a conventional IC, and the integrated power transistor is not larger than an equivalent discrete. This process finally makes high-voltage ICs for power control practical.
With this advanced high-voltage process, designers can control power directly from the ac line without the need to step-down the voltage in the power section. One such application is in stepper-motor drives, which currently require a 40-V power supply that’s larger than the motor and its controller combined. The process eliminates that supply by allowing the stepper to be powered straight from the ac line voltages. A PC that controls a burglar-alarm system can also be considered. Designers can now get an IC that links directly from the wall outlet’s 120-V ac to the computer’s 5-V dc control logic.
Historically, new markets are created by each new innovation in semiconductors: transistors were responsible for compact radios and audio products, and microprocessors brought about the age of computing. High-voltage ICs will revolutionize the way we think about the electro-mechanical world. Such components as motors, relays, and sensors have remained the same over the years, but applying modern electronics to them will create major changes.
As we proceed into the 1990s, we’ll see smarter electrical products. For example, electrical outlet boxes in future smart homes will be programmable from a central computer. Not only will they turn on appliances and lighting fixtures, but they’ll have built-in intelligence to protect themselves against unsafe power drains from appliances. Temperature sensors will be built into common products, such as cooking utensils, to protect them from dangerous heat levels that could cause a fire. Using digital techniques to control power will lead to many innovations that we haven’t yet thought about.