Virtual remote sense controller overcomes the need for remote sense wires
April 15, 2010 // Paul Buckley
A Virtual Remote Sense (VRS) DC/DC controller that eliminates the remote sense wires required to compensate for the voltage drop in cables, wires and circuit board trace runs has been unveiled by Linear Technology Corporation.
Voltage drops in wiring and cables that cause load regulation errors are usually corrected by an additional set of sensing wires but Linear’s LT4180 continuously interrogates the line impedance and corrects the regulator’s output voltage.
As a load current increases, the voltage drop (IR losses) in the wiring increases (due to the line impedance) and the voltage delivered to the system drops. The traditional approach to solving such a problem is to sense the output voltage with a pair of wires that run from the regulator’s feedback network to the load. While this approach works well, the additional pair of wires may not be practical or reliable.
The LT4180 is designed to maintain a corrected regulated voltage at the load regardless of current or line impedance. The 3 V to 50 V input voltage range address a variety of applications, including remote instrumentation, battery charging, wall adaptors, notebook power, surveillance equipment and halogen lighting.
The LT4180’s key benefits are achieved by the device continuously interrogating the line impedance and correcting the power supply output voltage to maintain a steady voltage at the load regardless of current changes. VRS works with a small modulation on the output of the regulator to compute the correction. The modulation is filtered by the output capacitor at the load. The LT4180 works with any conversion topology and isolated or non-isolated power supplies, DC/DC converter including bricks, modules and adjustable linear regulators.
The output correction is obtained by modulating the output and measuring the incremental change in voltage that occurs with a change in current. Any modulation noise is eliminated by the supply bypass capacitor located at the load.
“The LT4180 provides a new function for power supply designers. Excellent regulation is obtained without sense wires, eliminating the need for point-of-load regulators,” explained Robert Dobkin, vice president of engineering and CTO for Linear Technology. “Difficult regulation problems such as long wire runs or system retrofits can be accommodated. With halogen lights, the light output drops more quickly than power, so keeping the correct voltage more than compensates for any additional cost of the power supply.”
Application benefits include:
Remote instrument sensors can be often connected by cables several thousand feet away from the base system. The LT4180 can be used to correct for a voltage drop in the wiring regardless of output current changes.
These devices can have an unacceptable voltage drop in the cable from the adaptor to the load. Some adaptor designs are done with a 4 conductor cable, two for the power and two for remotes sense wires. The LT4180 can compensate for this voltage drop and eliminate the need for a 4 conductor cable.
Notebook Computer Power
The high current needed for fast battery charging in notebook and netbook computers gives poor regulation at the computer. The LT4180 can easily maintain an accurate voltage through the output cable over the entire charge current range.
Remote Surveillance Equipment
This type of equipment is normally made up of remote cameras used to cover a wide area. These cameras are controller by a base unit and can be several hundred feet away causing regulation errors.
A 10 percent error in voltage results in a 30 percent change in light output when driving Halogen bulbs. It’s easy to get a 1 volt drop (with a 12V system) in the wiring, decreasing the light intensity and changing its color temperature. The use of the LT4180 in this application saves energy and maintains the right color temperature.
Availability and Pricing
Three temperature grades are available: an extended grade version from -40 to 85 degrees C, an industrial grade version from -40 to 125 degrees C and a military grade option from -55 to 125 degrees C. The 1,000-piece price starts at 2.95 US Dollars each. The LT4180 is offered in an SSOP-24 package. All versions are available from stock.
Related link: www.linear.com All news
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