This dummy load can be very helpful in testing power supplies, storage batteries, and similar devices. It has a variable load resistance and enough current handling capacity.
Ordinary dummy loads are usually made of fixed value resistors. They are cheap, readily available, and easy to assemble. But for power dissipations above 10 watts,
it is quite difficult to find the appropriate resistors. Their load resistance value is also fixed.
One excellent solution to this problem is using a dynamic dummy load. This dummy load not only can dissipate high power levels, but its load resistance can also be varied.
The circuit featured here uses a 2N3055 transistor with an emitter resistance of 1 ohm per 5 watts. It functions as a variable current sink.
The current flowing through the transistor can be varied by applying a voltage at its base. The load current value (IL) can be found with the ff: formula:
IL = (UV=UBE)/ R
UV = base control voltage
UBE = base-emitter voltage
R = resistance at the emitter
The 2N3055 transistor must be heatsinked.
The heatsink helps the transistor handle loads up to 45 watts.
Parts Placement Layout
Electronic Circuits volume 1.0 - Circuit Nr. 17
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.