Last updated on 2025-11-10 at 10:09 EST (UTC-05:00)
From Hammond to High Efficiency: Reflections on Power Supplies Then and Now
In 1985, when I started my career at GFC Hammond Electronics in Guelph, Ontario, the hum of transformers and the scent of flux were part of my daily environment. As a production test technician, my job was to test and repair linear and switching power supplies—work that gave me an intuitive feel for what really makes electronic systems tick.
The Hammond facility on Curtis Road was a fascinating place for someone just starting out in electronics. The Hammond Museum of Radio was located in the same building, and the local amateur radio club’s repeater, VE3HC, had a tower at the back of the plant. Fred Hammond himself—whose name is etched into Canadian radio history—could often be found tinkering or chatting with staff. For a young technician like me, those were inspiring encounters that linked the practical side of my work to a century of radio innovation.
Understanding the Foundations
To appreciate modern power supplies, it helps to look back to the origins of the electrical grid itself. The way we generate and distribute electricity has always shaped the way we convert it.
In the late 19th century, the “War of the Currents” pitted two of the era’s greatest inventors against each other: Thomas Edison, who favoured direct current (DC), and Nikola Tesla, whose alternating current (AC) system was backed by George Westinghouse. Edison’s DC approach had the advantage of simplicity and safety, but it couldn’t transmit power efficiently over long distances. Tesla’s AC system, on the other hand, used transformers to step voltage up for transmission and down for use—making large-scale distribution practical for the first time.
The debate was settled decisively in 1895, when the Niagara Falls hydroelectric plant—built by Westinghouse—demonstrated the superiority of AC power. The plant’s generators produced 25 Hz alternating current, a frequency chosen as a compromise between efficient motor operation and adequate lighting performance. While 25 Hz served early heavy industry well, it wasn’t ideal for all applications. By the early 20th century, 60 Hz had become North America’s standard, striking a balance between efficiency and performance for the emerging electrical grid. [2]
Across the Atlantic, Europe standardized on 50 Hz, largely through the influence of engineers at AEG and the VDE. They determined that 50 Hz offered the best trade-off between voltage drop, lighting flicker, and motor design. The choice was also elegantly compatible with the metric system—a detail the Germans took no small satisfaction in noting. [1]
These early engineering decisions still echo in our wall sockets today. The world’s grids may differ by frequency and voltage, but they all deliver alternating current—a form of power distribution optimized for transmission, not for the needs of modern electronics.
Why Electronics Need Conversion
For electronic systems, line-frequency AC power isn’t directly useful. Radios, computers, and control circuits all require direct current (DC)—and not just any DC, but clean, stable, and precisely regulated voltage. This is where power converters come in: they transform AC into DC and sometimes back into AC at different frequencies for specialized uses, such as motor drives or RF systems.
This need for efficient and reliable power conversion drives the evolution from linear to switch-mode power supplies—the very technologies I worked on daily at Hammond.
Linear Power Supplies
In a traditional linear power supply, the transformer does the heavy lifting, stepping up or down the voltage and isolating the circuit from the mains. The rectifier converts AC to DC—first through simple half- or full-wave circuits and later through the now-ubiquitous bridge rectifier. The resulting pulsating DC is smoothed by large electrolytic capacitors, which store charge between cycles to reduce ripple.
Filtering and regulation define the character of a linear supply. Early designs used Zener diodes or discrete transistor regulators, which three-terminal IC regulators, such as the LM78xx series later replaced. Linear regulators operate in the transistor’s linear region, dropping excess voltage as heat—a simple, reliable, and noisy (in the thermal sense) way to achieve a stable output.
Linear supplies have an unmistakable presence: heavy transformers, warm chassis, and that faint 120-Hz hum that signalled a tired filter capacitor. They were dependable, repairable, and forgiving—a good match for the analog age.
Because linear supplies operate in the linear region of the transistors, the difference between the raw rectified DC and the output voltage must be dropped across the regulator transistor(s), resulting in significant I2R losses in those devices. [4], [5].
From Linear to Switching
By the time I arrived at Hammond, switch-mode power supplies (SMPS) were reshaping the field. Instead of relying on bulky transformers at 60 Hz, SMPS designs rectify the AC first, then chop the DC at high frequency—tens or hundreds of kilohertz—using transistors operating in saturation (fully on or off). The high frequency allows much smaller transformers and capacitors, dramatically improving efficiency and reducing weight.
Of course, early SMPS units had their quirks. Without proper filtering—MOVs, chokes, and capacitors on the input—they could fill an HF receiver’s spectrum with a wash of interference. However, as designs matured, improved EMI filters, shielding, and power factor correction made switching supplies both quieter and more efficient.
How switching power supplies work
In switch-mode supplies, the AC mains power is first rectified. Then, the DC power is converted back to AC at a much higher frequency, allowing smaller, lighter, and less expensive transformers to be used to provide the lower AC voltages needed for the load(s). The use of higher frequencies also means that the filter capacitors can be smaller in size and lighter in weight. Additional inductors are required to prevent high-frequency switching noise from transferring to the load side of the supply. The benefit is that the primary power converter can use pulse-width modulation, keeping the switching transistors operating in their saturation mode, and thereby reducing the I2R losses in the transistors that result in waste heat. [6], [7].
What’s easy to forget is that early SMPS units were not always well-behaved neighbours in a radio shack. Without proper transient filtering—MOVs, chokes, and capacitors on the input—they could turn the HF spectrum into a wash of hash. Today’s designs, with improved EMI filtering and power factor correction, are worlds better.
Lessons That Endure
Looking back, my time at Hammond laid a foundation for everything that followed. Power supplies are not just supporting components; they’re the heart of every electronic system. If the supply isn’t clean, stable, and appropriately rated, nothing downstream behaves as intended.
Al Penney’s excellent presentation [3] on power supplies for amateur radio operators captures that same truth: whether you’re winding transformers, testing LM7805 regulators, or designing 90%-efficient SMPS circuits, the goal remains constant—reliable, safe power delivery.
For me, that journey began on a test bench in Guelph, soldering iron in one hand and scope probe in the other—under the same roof where Fred Hammond preserved the history of radio. It’s a fitting reminder that every modern innovation, no matter how advanced, still rests on a well-built power supply.
References
[1] G. Neidhöfer, ‘50-Hz Frequency [History]’, IEEE Power and Energy Mag., vol. 9, no. 4, pp. 66–81, July 2011, doi: 10.1109/MPE.2011.941165.
[2] P. Mixon, ‘Technical origins of 60 Hz as the standard AC frequency in North America’, IEEE Power Eng. Rev., vol. 19, no. 3, pp. 35–37, Mar. 1999, doi: 10.1109/MPER.1999.1036103.
[3] A. Penney, Power Supplies, VO1NO, RAC Basic Amateur Radio Course, 2023.
[4] O. M. Urias, ‘How to Build a DC Linear Power Supply’, Build Electronic Circuits. Accessed: Oct. 30, 2025. [Online]. Available: https://www.build-electronic-circuits.com/linear-power-supply/
[5] ‘Power Supply Circuits’, in Lessons in Electric Circuits. Accessed: Oct. 29, 2025. [Online]. Available: https://www.allaboutcircuits.com/textbook/semiconductors/chpt-9/power-supply-circuits/
[6] “Switching Mode Power Supplies,” Wikipedia. [Online]. Available: https://en.wikipedia.org/wiki/Switched-mode_power_supply
[7] C. Atwell, ‘A Brief History of Switching Power Supplies’, Electronic Design. Accessed: Nov. 07, 2025. [Online]. Available: https://www.electronicdesign.com/technologies/power/article/55040799/electronic-design-switching-power-supply-history-from-theory-to-design-essential
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