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Well it depends on where it has been used. For example an instrument for calibration, testing may temporarily connect output to a dummy load and after calibration, testing,... disconnect it.
In switching power supplies also to reduce noise when current is low, the device may parallel a dummy load and when actual load current becomes more than a certain amount the dummy load will be disconnected.
It could be a resistor or more complex circuit which is used to simulate a load for testing an electrical circuit. (An e-load for example). It could be a resistor which is connected to the output of some IC which needs to source some current to operate correctly or output some voltage. Sometimes it could be used to connect some floating outputs to ground, in case you wanted take open circuit voltage measurements from that output. It could also be used for testing audio amplifier circuits without producing intense sound. Their application in SMPS's are already told here.
In switching power supplies also to reduce noise when current is low, the device may parallel a dummy load and when actual load current becomes more than a certain amount the dummy load will be disconnected.
But what for if the last circuit doesn't need its appearance ? Does it help to choose the right device or right compents ?
And where do you think that you must need dummy load for test ?
Thanks !!!
An example from RF: Imagine you have a transmitter, an antenna and a cable to connect them both.
Transmitter ---------cable--------- Antenna
If you now switch on the transmitter and disconnect the antenna, all the power will be reflected at the end of the cable and will go back into your transmitter - and will probably blow it up (just to say it in easy words, it's RF theory).
So if you're going to test something with your transmitter without an antenna connected, you need a dummy load at the end of the cable to dissipate the power. The Impedance of the dummy load usually is the same as the characteristic impedance of the transmission line, this prevents high magnitude reflections back into the transmitter.
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