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High-voltage IC technology for bias supply design

Posted: 13 Apr 2015 ?? ?Print Version ?Bookmark and Share

Keywords:bias supply? radio frequency? AC/DC? DC/DC switching converter? MOSFET?

High-voltage IC technology can address these design challenges, enabling designers to reduce their component count and design-cycle times significantly. A high-voltage switcher such as the UCC28880 (figure 4) integrates a 700-V power MOSFET, a high-voltage current source for start-up, current-sensing, control circuitry and fault protection in a compact SO-7 package. The switcher incorporates a soft-start feature for controlled power stage start-up to minimise stress on the power stage components.

With smart power management, its bias current consumption is reduced to less than 100 uA. This means that the switcher can be self-biased from the AC input during normal operation and standby without significantly impacting overall system power consumption. Output voltage regulation is achieved by replicating the output voltage on capacitor C4 during the off time of the buck converter. The switcher implements smart over-load protection by increasing the converter off time during over-load and short-circuit conditions to prevent inductor current runaway and MOSFET overstress.

It also incorporates an over-temperature monitoring circuit to protect itself and the system during an over-temperature fault condition. The switcher can be used in various application topologies with direct or isolated feedback, and in low-side or high-side buck configurations, depending on the application bias needs. Efficiency and output regulation accuracy for a universal AC-input bias supply with 13V/100 mA output is shown in figure 5. The UCC28880 varies the converter switching frequency across load to enable a flat efficiency curve with best-in-class average efficiency.

Figure 4: Non-isolated buck converter in high-side configuration.

Figure 5: Efficiency and output voltage accuracy for a 1.3 W bias supply.

Summary
Off-line bias-supply design specifications and performance requirements vary widely, based on the application and end equipment. However, most system designers are seeking low component count solutions that offer ease of use and simple scaling to reduce overall system design cycle time. In this article, we discussed how high-voltage IC technology and how smart power management can greatly simplify non-isolated AC/DC bias power supply designs. Provided as an example is the UCC28880 700-V switcher which enables robust, low-cost, transformer-less designs using standard off-the-shelf components to deliver best-in-class efficiency and standby power performance.

Note
1) European Commission's Ecodesign Directive for energy-related products (ErP) Lot 6, Tier 2 requirement for household and office equipment effective in 2013 limits total system standby power consumption to less than 0.5 W.

About the author
Adnaan Lokhandwala is Product Manager at Texas Instruments.


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