Measuring variable frequency current

[BorisRap]

Hi guys,

I'm doing a project in which I have to measure the current through a laser diode and read it with a micro controller.

Here is the catch: The diode is controlled by an IC that varies the current and also performs some modulation. The current can vary from 1A to 3A and the modulation can be from DC to 2Mhz.

I don't need to know the instantaneous current in the diode, getting some rough approximation is ok, it's just for safety reasons, to turn off the diode if too much current is being drawn.

Due to the control IC topology the current must be high side measured.

What simple solutions would yo recommend? I know that maintaining the gain in a 2Mhz bandwidth span is no easy job.

Thanks for your help!

[MarkT]

Simple, low-pass filter the current signal with an RC circuit.  Then the bandwidth can be low, 10Hz or whatever is sensible for warning of overheating.

With a high-side shunt you would low-pass filter the signal from both sides of the shunt independently so that common-mode and differential signals are both band-limited.

[Benta]

I thought most lased diodes have a built-in photodiode for this function.
What laser diode is it?

[PCB.Wiz]

I don't need to know the instantaneous current in the diode, getting some rough approximation is ok, it's just for safety reasons, to turn off the diode if too much current is being drawn.

Is this eye safety, or diode safety ?

This is really a eFuse or circuit breaker type problem, so the MCU can be used to set the trip point (if that needs to be variable), but not be involved in the turn-off.

TI's load Switches section for example, has many devices and some include current set and cut-off.

Or, you can just use a simple current limiting element, in series with the diode.