If you are testing various power supplies (switching or traditional), surely you will need a test load, whose current consumption can be
regulated. Such a dummy load can help you to find out exactly the current threshold, where the ripple starts to occur, the current limit kicks in, the output
voltage start to fall or the electronic fuse turns off.
My dummy load is very simple. A MOSFET-N transistor is used here to turn the input power into heat. Current consumption is varied by changing the
gate voltage using a potentiometer. MOSFET resistance is dependent on the gate voltage. The voltage
for the potentiometer is regulated using Zener diode. In order to test a power supply with a low output voltage,
you should use the logic-MOSFET (a MOSFET designed to be driven with logic level). It has a low gate threshold voltage
and allows to test power supplies with voltages down to about 4V. For logic MOSFETs is suitable 4.3V Zener diode, for traditional MOSFETs about 7.5V Zener.
MOSFET must be mounted on a large heatsink. For short duration tests, a smaller heatsink can be sufficient.
The maximum power dissipation depends on the type of the transistor and the heatsink.
My electronic dummy load operates in the input voltage range of about 4 - 28V. Logic MOSFETs have usually the max D-S voltage
30V. Never exceed the maximum voltage rating of the transistor.
When using an appropriate MOSFET, this dummy load can work with higher voltages. In this case, increase the value of R1 resistor.
Warning - a dummy load may get very hot! Risk of fire! Never operate it unattended.
You may add a current and thermal fuse for extra safety.
