We make "dummy load" devices out of stacks of fast power rectifier diodes, often with a little series resistance. LDs often have hundreds of Megahertz to Gigahertz bandwidths.. The oscope may or may not catch the destructive surge. It's that fast.
Very, very, careful design is needed.
In my case the current supply is designed so the external control loop opamps are powered and stable long before power is even applied to the current loop. poles and zeros matter. Commercial drivers are not that expensive.
You will find fools publishing designs using large series resistors, often inductive ones, for fiber coupled laser current sources. Beware. [Note, for tiny diodes, the lm317 regulator in constant current scheme is known to have a clean startup, just don't put a potentiometer in as a current control, as the wiper of a potentiometer often lifts as its turning"]
Non-inductive current sense resistors in the tail of the voltage controlled current source are important. I'm not so sure I'd trust Spice for this, most opamp models are not covering the startup state of the opamps internal current sources/sinks.
Steve
Last edited by mixedgas; 10-07-2023 at 18:48.
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