Offboard AC/DC Power Supplies Bring a Wide Range of Options and Cost Efficiency

As a bright-eyed manufacturing engineering graduate, one of my first jobs was assisting a senior engineer with designing an AC/DC switching power supply for a high-end industrial proportional integral derivative (PID) controller. My “help” largely comprised replenishing the coffee cups and sourcing breadboard components. However, he was a patient and knowledgeable mentor, and I learned more about designing a power supply from scratch in a few weeks than during an entire semester at college.

Afterward, I even managed to turn out one or two useable switching power supply designs of my own, albeit based on architectures borrowed (with permission) from the senior engineer.

A few years later, the company I worked for found it more cost-effective to buy modular AC/DC power supplies off-the-shelf from a commercial vendor rather than create our own. The result was a little less fun for the designers, but our experience was still vital for ensuring we selected the best commercial solution to meet our product’s specifications.

Matching a power supply to the application

Knowledge of engineering parameters such as efficiency, input inrush current, ripple and noise, and start-up overshoot voltage enabled us to test and verify the commercial solutions to ensure they matched the power demands of the industrial PID controllers, and offer decent regulation and extended mean time between failure (MTBF).

However, matching a commercial solution to the application’s product specification was easier said than done because, back then, the range of solutions from each supplier tended to be restricted to just a few variants. On top of that, after our budget constraints were factored in, that range of variants became even fewer. This often meant specifying a power supply that would work reasonably well, but usually represented something of a compromise.

For example, there were times when we ended up with a commercial power supply that, while adequately meeting our controllers' current and voltage demands, would often operate outside of its most efficient output range, particularly at low loads. The result was additional power dissipation and thermal management challenges we could have done without.

Extending the range

The world of modular power supplies has changed for the better in the decades since I scratched out my rudimentary designs. Now, the scope of commercial off-the-shelf solutions is breathtaking, and ranges are not restricted when budgets are tight.

Take, for example, TRACO Power’s line of industrial AC/DC power supplies. The company has added four new power levels to its already wide-ranging TXN Series. The units now have 35, 200, 350, or 800 watt outputs, and can be specified for each power level with an output voltage of 12, 15, 24, or 48 volts. For the 35 watt version, 3.3 and 5 volt options are also available. Examples from the product range include the TXN 35-124, a 35 watt, 24 volt AC/DC power supply; the TXN 200-124 at 200 watts and 24 volts; the TXN 350-115 at 350 watts and 15 volts (Figure 1), and the TXN 800-148 at 800 watts and 48 volts.

Figure 1: The TXN 350-115 350 watt power supply outputs 15 volts DC from an AC input of 90 to 260 volts. (Image source: TRACO Power)

The power supplies are housed in metal frames and employ screw terminal block connectors. They are the most cost-efficient encased AC/DC product series the company offers. Features include 3000 volts AC (VAC) reinforced I/O isolation, an internal EN55032 class B filter to reduce conducted and radiated emissions, active power factor correction (PFC) above 100 watts, IEC/EN/UL 62368-1 safety approvals, and compliance with EN 61000-3-2 for electromagnetic compatibility (EMC). The units even feature an internal fan for forced cooling.

Performance at a keen price

However, the cost efficiency of the TRACO Power TXN Series hasn’t resulted in performance compromises. For example, the TXN 350-115 has an input range of 90 to 260 VAC and an operating temperature range of -30 to 70˚C. It supplies an adjustable nominal output voltage (V_out(nom)) between 13.5 and 15.5 volts at a maximum output current (I_out(max)) of 22 amperes (A) for a maximum output power of 330 watts.

For a 230 volt input, the active PFC is 0.95. The voltage set accuracy is ±1%, regulation varies by 1% across a load variation of 10 to 90%, and output voltage ripple is a maximum of 150 millivolts peak-to-peak (mV_p-p) (Figure 2). The power supply features a 110 to 160% I_out(max) output current limitation and 110 to 140% V_out(nom) overvoltage protection. The MTBF is 230,600 hours.

Figure 2 : The TXN 350-115 exhibits a maximum output voltage ripple of 150 mVp-p, helping mitigate EMC challenges. (Image source: TRACO Power)

The flat efficiency curve of the TRACO Power units helps mitigate the temperature and power dissipation challenges I faced in my younger days when using lesser power supplies. Even from a relatively low load of around 20%, the TXN 350-115 exhibits an efficiency of over 75% (Figure 3).

Figure 3 : The TXN 350-115 exhibits an efficiency of over 75% for loads over 20%. This helps ease power dissipation challenges. (Image source: TRACO Power)

Conclusion

While I enjoyed designing an offboard AC/DC industrial power supply from scratch, off-the-shelf solutions save project time and allow engineering teams to focus on other aspects of the end product. Moreover, such is the range of today’s power supply options that it is possible to source a solution that comes very close to offering the optimum performance and efficiency for virtually any application.