85W laser array driver circuit

Question

I have an OSRAM 85W 450nnm laser array.

It's essentially a large 'chip' with 24 integrated laser diodes (break it down they're approx 3.5W diodes each.) The Chinese source I purchased it from also sold me a "laser driver" which I've quickly determined is just a boost converter of some kind with no current control whatsoever. I've already designed and produced a circuit (with current and case temperature feedback data) which has the array in a series configuration, meaning you could imagine the diode as one big diode with a compliance voltage of 105 to 110V and 2.5A maximum. The cooling part of the equation has been solved, powering the diode in the manner described definitely works - quite well infact.

I happen to have 3 N-channel 200V 30A MOSFETs (NTB30N200T4G) from an old project, so if they're usable in the design even better.

I've two trains of thought for this:

1. DC-DC approach, start with a 12V or 24V SLA battery or similar high current DC source and create a boost circuit to attain 110V. Then I build a laser driver fed by the power source.

2. AC 240V through a custom made transformer, nice and simple 1:2 ratio for a 120V output, bridge rectifier and DC cleanup then voila I have my 110V with plenty of current to spare. Then regulate voltage and current (MOSFETs might come in handy here?) to construct my laser driver circuit.

Does anyone with more experience with power supply design or more specifically laser power supply design have any input, ideas?

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Partially answered my own question for those reading who may be interested in the solution i've found. Datasheet for diode below for further context:

Sourced a 300VAC Toroidal 240 primary -> 55V - 55V secondary transformer. With the taps joined provides an ideal 110VAC RMS output. This will be used to form a basic power supply with filtering to clean up DC, buck converter to reduce voltage to desired range. See datasheet for min (20.7V) to max (28.8V) forward voltage per channel, with all 4 channels in series this yields a requirement of lower bound 82.8VDC up to 115.2VDC (Perhaps this explains my earlier desire for a 110VDC supply..).

Datasheet for toroidal transformer: https://au.rs-online.com/web/p/toroidal-transformers/2238241/

My question remaining is: what is an ideal circuit topology for voltage and current regulation (110VAC RMS, 2.73A)?

Answer 1

Firstly, I'm going to assume you've got enough laser safety qualifications and protective equipment to work with 85W safely, where even transient reflections can blind bystanders instantly. That's a class 4, so you need a key switch and a safety interlock to keep humans out of the area in which the beam could be.

I don't see any advantages for the battery approach unless you somehow need this to be terrifyingly portable, so I would take the mains approach.

Power transfer can only be achieved in those parts of the cycle where the input voltage exceeds the output voltage; since the output is rather high, I don't see the advantage of the 2:1 transformer other than isolation, since the voltage on the output (both AC and DC) is also lethal. From there it's "just" a very high voltage buck converter with a fairly large capacitor on the output.

Safety interlocks go on the output side.