I am looking into possible methods of protecting against small current transients for use with a laser module and am having trouble finding information, partly because I am unsure what exactly to be looking for.

The laser generally runs around 180mA in small bursts when the system is in use and I have plenty of active protection in the way of microcontrollers in the system but my concern is possible transients that could damage the laser if there is no power to the system or if the processors are otherwise in a state unable to handle such small transients. I am speaking specifically of not allowing anything above, say, 300mA through the laser. I have tried searching for components having to do with current and transient suppression but they typically deal with power and EMI/EMC levels which are far outside of what I am looking for.

There is a small set of Transient Current Suppressors (TCS) by Bourns such as the TCS-DL004-500-WH which appear to be very close to what I am looking for although this appears to be proprietary technology and the range of max currents is small (250, 500 and 750 mA).

I am really looking for anything that might be similar or if there are particular circuit topologies that would generally do well dealing with this situation I am unsure what those would be or what to even start researching.

Anything to point me in a more targeted direction would be greatly appreciated.


1 Answer 1


I suggest a twofold strategy:

  1. use low inductance capacitive shunting around your laser diode. The laser has an instantaneous resistance of several ohms (Vf / 180mA). So build something that is in the mohms for frequencies above e.g. 10 MHz, e.g. using MLCCs. In addition, you can add an inductor/bead in series with the laser.

  2. a semiconductor current limiter inline with your laser diode. This can be either the conventional two-transistor "constant current sink" circuit. Or even a single depletion MOSFET + resistor. Since these circuits take some ns to "act", it is important to have (1) in addition.

Taken together, these should limit current spikes between DC and ~1GHz. The integrated parts that you mention, likely use a variation of (2). If you use your own MOSFET + resistor instead, you will have better control of blocking voltage and limit current. You will probably also save component cost.


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