LT3081 Parallel Configuration for Laser Diode Drive

Question

Hi, 
 I'm working on powering a laser diode (1.8 V, up to 9 A) by paralleling multiple LT3081 linear regulators. My plan is to use three LT3081s in parallel to deliver up to 4.5 A (1.5 A per LT3081), and potentially more if needed. I&rsquo;ve set this up in LTspice, and I&rsquo;ve attached a screenshot and the simulation for reference (please disregards voltage sources at 0). 
 In my circuit, I&rsquo;m using a potentiometer at R4 to adjust the current limit, and another at R11 to set the output voltage. 
 I have a couple of questions regarding the behavior of these potentiometers: I have read that you can ground the SET pin, so If I remove R4 and R3, will the LT3081 automatically set the output voltage based on the load demand? In my case, the laser operates at 1.8 V - would that voltage be maintained? 
 Since laser diodes are current-driven devices, how critical is the voltage setting at the SET pin? In the simulation, I set the output voltage to around 1.9 V to prevent overdriving the laser. However, I'm concerned - if I accidentally set the voltage too high (e.g., 3 V), would the LT3081 try to force that voltage and potentially damage the laser? By the way, in the simulation when the SET is to ground, the simulation does not work properly. 
 I also read in the documentation of the LT3081 that it can be configured as current source, but I am not sure if they can be paralleling or how to achieve it and if thermals will be problematic for the current I would like to get. 
 Any guidance would be greatly appreciated. 
 Thanks! 
 3731.LT3081_TA01A_triplecurrreg.asc

ARad · Accepted Answer

I attached an image of one way to make a current source for a 9A LED that is controllable with a digital potentiometer. I am a little busy these days, so I probably won't be able to engage further, but my advice is to make a clear, realistic specification for what you want to accomplish and start with a reference design that you can adapt to your needs.)

JRod84 · Answer

Thank you so much for your feedback, much appreciated! I will start with your suggestion. Just wondering why the approach I made is wrong or not appropriated for my design, I know that current source is the most appropriate for laser, but the one I made could also work? and no worries, any time you could have in future to give me more insights on this will be much appreciated. 
 Oh, I also realized that your approach is using LT3083. I was interested to use the LT3081 because of the current and temperature monitoring capabilities.

GonzalezAl · Answer

Hello there, so I realize that this question was posted in 2025, but here are some of my suggested answers based on the distinct questions within this post. For my response I am listing the question I believe you asked, followed by my response: Q: Can you configure these regulators as current sources in parallel? A: Yes, assuming the load draws a current lower than the maximum per regulator, the output should receive current from each of the components to supply a larger output current. Q: What happens if the set pin is connected straight to ground? A: The voltage generated will be the minimum allowed voltage value at the output, and the internal circuit is essentially a non inverting Op-Amp voltage follower that sees 0 [V]. Q: Does does it automatically set the output voltage based on loading? Additionally, Will the regulators maintain 1.8 [V] automatically with the laser as a load? A: No, the voltage is set based on the externally attached set resistor. Since there is a 50 [uA] current flowing out of the SET pin, the resistance value connected from that pin to ground will determine the voltage seen at the output pin, not the load itself. Q: If the voltage is set too high, does the regulator force a higher voltage, despite the load connected not requiring it? A: The regulator's job is to maintain a steady voltage based on the reference created on the SET pin, therefore, if you choose a resistance value that results in a high voltage to be driven, that voltage will be seen at the output, although only the required current will be drawn either based on the current limit or the current draw required. Q: Would thermals be an issue? (Two separate approaches) A: Looking at the resistors NEAR the high current draw, it seems like your design doesn't dissipate much power through them, meaning that thermals should be okay. A: Looking at the LT spice model and seeing a Vin of 3.3 [V] as well as a Vout of around 1.8 [V] lets say, the resulting power drop while attempting to reach 1.5 [A] yields about a 1 [W] dissipated for the regulator by itself, if you consider the power dissipation chart on the datasheet should mean that the LT3081 should safely operate within the majority of its temperature range without functionality issues.

SLA Status	Assignee	Support Status
SLA Closed. Met after 18 hours	MStokowski ARad EarlJohn cjjardin ACaldejon	Open

Popular Forums

Product Forums

Application Forums

Design Center Forums

Highlighted Webinar

Places

Libraries

Upcoming Learning & Events

Challenge Yourself!

What's Brewing

Places

Resources

Visit ContentZone

The Latest Read

New Release

Recent Technical Insights

SLA Information

Products Mentioned

Thread Details

LT3081 Parallel Configuration for Laser Diode Drive

Thread Summary

Thread Notes

Before You Switch