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Thinking through a design that interfaces a solar panel to a 12V diaphragm pump, and considering the interfacing options. I've come across the term "Linear Current Booster", and wanted to explore this idea further.

While the concept of "MPPT" controllers is fairly well documented for solar panel to battery systems (and ICs are marketed for this purpose, like the fairly fancy Linear LT8490), I'm not seeing as much documentation around the Linear Current Booster.

I understand the concept of a Linear Current Booster as a DC-DC converter that:

  • Reduces a solar panel voltage to a lower output voltage, and increases output current,
  • Ensures that the minimum output voltage is above some threshold (how does it determine this?) to ensure that the pump does not run at 0V; which would be effectively running at 0 RPM and burn out the windings in time,
  • Ensures that the maximum output voltage is limited, to ensure that the pump does not overspeed.

The advantage (as I understand it) is to be able to operate in lower light conditions; when the panel could not provide enough current to the pump to give it enough torque to start moving if it was directly connected.

Some examples of commercially available Linear Current Boosters:

  1. EAST LCB
  2. SolarConduit LCB
  3. Clean Energy Brands LCB

So, does anyone here have any insights on the difference between a DC-DC buck converter and an LCB? I think that all of the functions of an LCB can be accomplished with a buck converter that implements an output undervoltage/overvoltage lockout. Is my understanding correct?

EDIT - It looks like the author of this buck converter design indicates that "Another application for this circuit is as a "linear current booster" (LCB). Common LCB uses include running motors and other devices directly from a solar panel with no battery. In the LCB mode of operation, it is possible to use the circuit to change a low current solar panel input to a higher current (but lower voltage) output."

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A buck converter, MPPT, and linear current booster are basically the same. The only difference is where you get the feedback from. For a power point solar controller, the input voltage is monitored. Below the power point voltage, the converter is faked out into thinking the output voltage is too high and shuts down. So the converter has to stay below the max output voltage and above minimum panel voltage. Typical MPPT hunt to find the best power point. Since power point only changes with temperature, you can track panels temp and be pretty close. If you just set a fixed power point voltage, you do just about as well.

Linear current booster acts in the same way. They generally have a fixed power point and often don't care about the output voltage. The motor is often used as the inductor in the buck conversion with a diode in parallel. I use the same process to heat water with PV efficiently.

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  • \$\begingroup\$ using the motor as the inductor is an interesting concept; but in this case, what would you be using as the feedback? The current through the motor-as-buck-converter inductor, or the voltage at the 'output' of the motor at the capacitor? \$\endgroup\$ – jjmilburn Jun 1 '15 at 1:10
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I think an LCB is sort of an adaptive buck converter, possibly a converter designed for constant current output. I have not been able to find a good schematic for comparison, however.

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  • \$\begingroup\$ I have not either, unfortunately. I wonder, though -- given that typically an MPPT has the luxury of a dump load (batteries) to push all of that power into, if the linear current booster acts in such a way that it does not operate the solar panel at the maximum power point. What I mean is, with a pump, I believe that you may have additional constraints (e.g. maximum current into the pump, maximum voltage across the pump) that may prevent MPPT operation. \$\endgroup\$ – jjmilburn Jan 30 '15 at 4:59

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