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This DC powerload is homemade with 10 big N-FET
It has two current ranges 0-6.5A and 0-75A
It can be set to be a constant-current load or a constant-resistor load.
A simple modification could add a Constant-Watt load possibility.
I have made this to test my homemade powersupply, to check if overload protection,
and shortcircuit protection works.
The schematic is so simple: just compare the voltage over a sense resistor with a variable voltage
the output of the opamp goes to the 10 gates, remember to have a 10-100 Ohm resistor in series with each gate,
This will prevent oscillation..
If the variable voltage is comming from the input loading voltage, you have a resistor type of load.
If the variable voltage is from a zener regulated voltage, you have a constant current load.
If the variable voltage is comming from the input loading voltage, but is inverted ! you have a constant watt type of load.
Here is a fast handdrawn schematic, due to all the requests.