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Question on testing/characterizing DCDC regulators (design process)
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David Hess:

--- Quote from: E.Buer on June 09, 2019, 09:37:30 am ---
--- Quote from: David Hess on June 08, 2019, 04:00:16 pm ---
--- Quote from: E.Buer on June 08, 2019, 02:29:53 pm ---Do you measure at different loads?
--- End quote ---

Yes, and different input and output voltages if applicable.  The loop response will change significantly if the regulator crosses the continuous conduction mode boundary and this will need to be taken into account in one way or another.  In discontinuous conduction mode, the loop response changes with load.
--- End quote ---

How would you go about testing this, using electronic loads, or simple power resistors? I guess it would not matter which is used, besides switching noise in the electronic load?
--- End quote ---

Electronic loads are not necessarily noisy but depending on the design they may interact with the frequency compensation.  Power resistors always work and you can buy really big power rheostats if necessary.

While not ideal, the output voltage of a variable output supply can be swept into a resistive load but depending on the design this may not be a sufficient test.
floobydust:
Simulate and test I use as a guideline, not the final result for industrial products.
Don't forget to include capacitance (and sometimes inductance) shifts due to temperature.
Noobs assume the components do not change, and ESR & value shifts can cause instability.
Go beyond tests in the lab- a temperature chamber should also be part of them.
David Hess:

--- Quote from: floobydust on June 10, 2019, 04:45:22 am ---Don't forget to include capacitance (and sometimes inductance) shifts due to temperature.
Noobs assume the components do not change, and ESR & value shifts can cause instability.
--- End quote ---

Something else to be wary of is transistor gain and Ft which can vary significantly between units.  It helps during development to have some worse or extreme case parts available.

If you were designing ATE equipment or pin drivers or something which has to power a difficult or unknown load, you might get esoteric and implement frequency compensation with less than 90 degrees of phase lag and 6dB/octave of rolloff but that is beyond a discussion of performance verification.  Such a control loop will remain stable into any capacitve load.
rbola35618:
If you don't have a FRA you could use a function generator, a Scope and a small transformer to inject a signal from the function generator and use the scope to measure the phase and gain of the feedback loop...



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