By going contrary to conventional thinking, a design team devised a more efficient regulator device for the DC-power path.
DC regulators are available in many different topologies, each offering tradeoffs in performance, size, efficiency, cost, and other factors. Regardless of their internal design, they all have one primary functional role: to accept a DC voltage input that may vary within a wide range and provide a constant DC voltage output independent of the load current it supplies and any changes in that current demand.
Terminology note: there are voltage regulators and voltage converters, and they have some functional differences, which we won’t detail here. However, engineers often use both terms interchangeably; we’ll stick with “regulator” here.
These regulators are available with three basic operating modes:
- Buck (step-down) regulators can only deliver an output voltage lower than the input voltage.
- Boost (step-up) regulators, which can only deliver an output voltage higher than the input voltage.
- Finally, the dual-mode buck-boost regulators can accept an input voltage that ranges below and above the desired output voltage and can transition seamlessly between buck and boost modes while still maintaining that desired voltage.
The typical efficiency of these regulators ranges between 80 and 95 percent, depending on the design, load characteristics, operating point, and other factors.
Note that we are focused here on switching regulators only, as the vast majority of regulators are in use. Their counterpart is the linear regulator, including the well-known low dropout regulator (LDO), which can only provide buck-mode operation and has far lower efficiencies on the order of 30 to 60 percent. They are used only in special circumstances where their virtues of low noise and fast response to load transients outweigh their inefficiency, thermal impact, and physical bulk.
In a typical power-rail path for a system with a higher-voltage DC primary rail, the source rail goes to Regulator #1, which produces a tightly regulated, intermediate bus-voltage output for lower-voltage Regulator #2, as shown in Figure 1. Regulator #2 then provides the final rail for the load.

Regulator #2 can also tolerate a fairly wide input-voltage swing and could be used with a poorly regulated input voltage. However, that enhanced tolerance in the input-voltage range is not needed since the output of Regulator #1 is already well regulated.
This means there Is redundancy with unneeded duplication of regulation effort; you might even call it “technical overkill.” Providing that regulated performance Regulator #2 is not cost-free but instead brings some losses and inefficiency.
Look at it this way: why should Regulator #1 be tasked with doing such a good job when Regulator #2 doesn’t need it and can deliver a tightly regulated output from a loosely regulated input?
What can be done
Recognizing this situation, designers at Linear Technology Corp. (LTC, now part of Analog Devices) decided to “think outside the (regulator) box” to see what could happen if they modified the performance characteristics of Regulator #1. This required doing more than simply loosening the specifications.
By implementing a clever twist on the regulator’s input-to-output relationship, they created a regulator that can deliver 99% efficiency when the input conditions are right – with “right” defined by the user. This was not just a thought or simulated exercise as they designed, fabricated, tested, and are selling an IC regulator (LT8210) with this new approach.
Here’s how this unconventional regulator works, as seen in the simplified overview diagram of Figure 2.

Instead of delivering a highly regulated output, Regulator #1 seamlessly shifts between three modes and does so without any user action:
- When the input voltage is below a user-set threshold, the LT8210 goes into boost mode, bringing the output up to the nominal value. This threshold is normally set at the lowest voltage Regulator #2 can accept as an input while still providing its regulated output.
- When the input voltage exceeds a different user-set threshold, it goes into buck mode to bring its output down to the nominal value. This threshold is normally set at the highest voltage Regulator #2 can accept as an input.
- However, when the input voltage to Regulator #1 is between the window limits set by the lower and upper thresholds, the LT8210 simply passes the input voltage to Regulator #2. It does this by turning on external FET switches, as seen in Figure 3. They call this “pass-through” mode.

What does this do for system performance? When the regulator is in that middle pass-through zone and not regulating, the only loss is due to the drain-source resistance RDS(ON) of a few milliohms. Therefore, efficiency goes up to 99+ percent — nearly perfect. Although this is only a few percentage points better than conventional performance, even a few points are meaningful in today’s world of run-time demands and thermal-dissipation challenges.
Summary
I don’t know if this product has been a commercial success, but that measure is not the point here. What does matter is that the design team looked at the fundamental issues of the regulation chain. They asked what was really needed, if conventional designs provided too much of a good thing, and if loosening performance strictures in a clever, transparent way would provide even modest benefits. Based on their assessment and analysis, they undertook an unconventional path to a very different solution to deal with the ever-present efficiency challenge.
References
LT8210 Data Sheet
Protecting and Powering Automotive Electronics Systems with No Switching Noise and 99.9% Efficiency
PassThru of a Voltage Using Buck-Boost Regulators
Why Using PassThru Technology Can Help Extend an Energy Storage System’s Life
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