What is the significance of load resistance simulation of converters

[aneesmohammed]

Hello all,

I would like to know the significance of putting a load resistor at the output side while designing a DC-DC Converter....For example, i am designing a 3KW DC-DC converter(assuming 400V 7.5A at output)....Then i put a 62.2 ohm resistor at output and measured voltage across it and getting around 400V DC...If i am using the same converter for some application whether I need to supply that 400V across the resistor to the load or I need to replace the resistor and connect the actual load instead?.... If so, does there exist such a 3KW rated resistance other than a huge rheostat?


I know these are the very basic level doubts that may be due to an improper understanding of the basic principles...But I love to build the fundamentals through forums !!!

 

[BradtheRad]

When you test various simulated loads you can see if problems crop up. Certain converters need a minimum load in order to work at all.
You're designing so your system so it powers the heaviest expected load. All components must be selected so they're strong links in your system.

A resistive load puts a straightforward burden on the system. However some other loads might be inductive or partially inductive (motor). Same with the capacitor side of things. These reactive loads try to draw current through switching devices at times in the cycle when the switches are supposed to be off. Either simulated or testing hardware, you are finding out if your system has weak links which risk breaking down as the load becomes heavier (impedance becomes less).

With different loads you can discover which type of filtering (example, L:C ratio) performs suitably in your system. And you may need to keep a minimum load on your converter full time, while also adding the heavy load you designed your system for.

 

[D.A.(Tony)Stewart]

Tungsten toasters, Nichrome hair dryers, or oil immersion heaters are low-budget options arranged in series that might have a resistance near target. Take your DMM to go shopping. Mind you the resistance rises with temperature a lot. This will give this supply better damping than any reactive load for step response. As you improve step response or phase margin in your Bode Plots, you can try a target load such as a motor with stored energy returned to the supply or dumped with a brake resistor.

A Light bulb at 2800'K takes about 10x the cold current as the hot current. Many DC motors have the same load effects with full power on start but with more inertia (time).

 

[dick_freebird]

The "load pole" is an element of loop stability and it likes to move around. Current sink and resistive and inductive loads and combinations of, are all possible applications and all must be checked.

IME current source (sink) load set very low is the worst ( LF load pole becomes dominant) and resistive loads are less likely to do so; resistor also "deQ's" the switcher LC output filter (/tank) which can ring up if "too ideal" passives and switches.