It is no secret that TI has been investing heavily in the industrial space. APEC is a great chance for us to show off some of the latest and greatest in power solutions for industrial applications, especially since TI has the most comprehensive isolated power portfolio all the way from wall to processor. In particular, one of the key demos not to miss is the isolated power design for programmable logic controllers (PLC) -the workhorse of industrial and factory automation environments.
This isolated design for powering the PLC is a DIN Rail mounted, offline AC/DC power supply that uses a primary side regulated (PSR) flyback controller, the UCC28630, to generate 24V at 65W from an AC input. This brand new Flyback controller, the UCC28630 has the unique capability of delivering up to 200% peak power (2x 65W = 130W!) for short time periods based on an in-built timer. This transient peak power capability does come very much in handy in industrial environments where a short burst of power is need to get that servo motor to start cranking up or to get those numerous sensing and diagnostic circuits to jump into action simultaneously when that smelting furnace need to fire up to produce metal from the ore.
The 24V is isolated from the AC input for safety reasons. PSR makes for an easier design because it eliminates the need for an opto-coupler, a TL431 reference and the compensation is fully internal. Tell a designer in the industrial world that ‘no opto-couplers are needed’ and I bet his eyes will light up. Opto-couplers, especially linear mode ones, have long been a point of concern due to wide parametric variations across temperature as well as long term reliability due to its inherent aging and wear-out mechanisms of the LED inside it. This is especially important in applications that typically have a long lifetime, like industrial.
A couple of other noteworthy features of the design, though not as critical for industrial applications, are high-voltage startup and X-cap discharge. The high-voltage start-up eliminates the need for startup resistors and makes industry’s best standby power (under no-load conditions) possible. The X-cap discharge helps to dissipate residual high-voltages in the input EMI-filter differential capacitors in a timely manner (when the AC plug is pulled), which are otherwise a safety hazard.
The isolated 24V is then fed into a PLC front end module board. The 24V is then passed through a hotswap controller (LM5069) for input current protection. The PLC board features the TI TivaTM MCU which is used to process factory diagnostic/sensing signals, and specifically in this demo it delivers a closed–loop, temperature control of a furnace with blowers and switch-off functions for regulating the temperature. In most industrial PLC applications, a second level of isolation and post-regulation on the downstream power rail is necessary in order to interface with and provide power to each of downstream circuit blocks (such as Input/output ADC/DAC modules, data processing MCUs, communication blocks, etc.) and the outside world (i.e. field sensors).
A simple way to achieve this isolation is to use a Fly-Buck converter. Brian King wrote a fantastic blog about Fly-Buck converters, check it out here. The Fly-Buck supplies used on the PLC demo board generate an isolated 24V, 3.3V. The LM5017 is used for 3.3V, the LM20242 is used for 24V.
I hope everyone is having a great APEC. Don’t forget to come by to see our demo! Click here to read all APEC 2014 blog posts on Power House.
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