A Quick Way To Determine Power Supply Output Resistance

Focus:

When dealing with slow-changing dc loads, like solenoids, brushed motors, heaters, etc., it is necessary to rapidly define a power supply output resistance in order to correctly assess the power supply load capability and tweak the feedback loop if necessary. There are diverse methods for defining the output impedance of a power supply, but some of these methods involve test instruments that may not always be available and/or produce more information than is needed for the loads in question. This article presents a highly simplified method requiring only a multimeter and a resistor of any value close to the load resistance. This method is based on measuring the voltage across the nominal load and the voltage across the load with the resistor in parallel. A simple calculation then yields the value of the power supply internal resistance plus that of the external wires.

What you’ll learn:

• How to simply determine the output resistance of power supplies for slow changing dc loads
• How to determine the output resistance of a power supply using only a multimeter and a resistor

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Author & Publication:

Gregory Mirsky, Vitesco Technologies, A Spinoff Of Continental Automotive Systems, Deer Park, Ill., How2Power Today, Nov 16 2020

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