Constant Current Power Load

By: Steve Hageman
This power load is suitable for testing power supplies to 100V and 10 Amps. Power dissipation is limited to 50 Watts continuous and 150 Watts for short periods of time.

The power load chassis is constructed from a 6 inch tall heat sink extrusion. The extrusion used had a slot cut in it that the front panel slips into. The circuitry is built on this front panel. The top and bottom panels, screw into the fins and hold the front panel in place. In the back view the IRF150 pass transistor can be seen. The knob controls the current that loads the power supply under test. One switch controls the power, the other switch changes the meter from reading the current to reading the voltage at the input terminals. The battery on the side is used to power the FET driver. having this battery on the outside of the load allows quick changing in case someone leaves the load on over a long weekend, draining the battery.

The load is useful in a lab environment to quickly check the output of a power supply.

The load works by adjusting the voltage across a precision current sense resistor to be the same as the reference voltage set by the knob. This provides a constant current output that is not affected by the load voltage.

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Modified - 7Jan02