Electronic Loads: CP, CV, CR.. how to implement?

[WillHuang]

Hi everyone, I'm making an electronic load using a microcontroller. I'm wondering how to implement the constant voltage, power, and resistance mode?

My problem is there's always a voltage drop along the conductor cables. If that happens, how do you truly get the desired output? For example, if I have a 5V input and I want a 1W constant power, I would need 200 mA. But at 200 mA, the voltage I measure is.. let's say 4.5V, making it 0.9W, even though the power supply is still outputting 5V. So, I am measuring 0.9W even though I am actually drawing 1W from the source. How do you get around this problem?

[Fire Doger]

You can implement +-Sense cables which will measure the voltage directly from PSU output.
Well designed PSU also have Sense cables to avoid voltage drop on cables.
It is called 4 terminal sensing.

[Kleinstein]

The CC and CV modes are somewhat similar to a lab power supply. The constant resistance mode is also possible to do analog or at least semi analog with an DAC used as a multiplier. The constant power mode is tricky, as this can be unstable in some cases. Even though it is possible to build an analog constant power mode one might be better of with feedback via the µC and this way have the option to chose from damping modes or warn if unstable.

[hugo]

Electronic DC Load 4 Part series by Scullcom Hobby Electronics :

[lukaq]

yep, ^^ this should be good