Driving a high power laser LED - Page 1
Forum section: electronics / projects

author: semir-t
author_rank: Regular Contributor
timestamp: December 21, 2022, 07:16:47 am
content: Hello all,I want to drive high power Laser LED manufactured by Kyocera. Datasheets states that the current for the Lase LED is around 2.2A and the typical forward voltage is around 6 volts. I need to have constant current driver and to make things even harder it needs to be battery operated.Is this even possible to do using a battery ? If it is, does someone have some tips on how to do this ? Links and other material would be helpful to.Thanks,

author: Faranight
author_rank: Unknown
timestamp: December 21, 2022, 07:47:10 am
content: Yes, you're going to need some sort of driver that is capable of limiting the output current. You said the forward voltage of this diode is 6V, but you never specified your battery voltage. What is it? I'm assuming it's higher than the Vf of the LED. I'd avoid a linear regulator here since you're gonna waste too much power on it, so you'll likely want a good buck converter with current limiting capabilities.EDIT: As an example, maybe take a look atTPS92512.Although this one is asynchronous, you'll likely want a synchronous one since it has a bit higher efficiency.

author: semir-t
author_rank: Regular Contributor
timestamp: December 21, 2022, 12:22:34 pm
content: I was thinking about using standard chargeable 3.7V battery.Idea was to use boost to get the higher voltage and then deliver that voltage though the MOSFET ( which would be controlled by PWM signal from the MCU) to the LED.But, as I need this light source for a sensor reading, I would need the constant current going through the LED so I can't control it using PWM.I am open to different battery if it helps me solve this problem. Idea is to have small portable device that could be charged.

author: semir-t
author_rank: Regular Contributor
timestamp: December 21, 2022, 12:25:27 pm
content: Maybe I could use 2S LiPo battery with the driver you have suggested. I would need to redesign charging part of the device but maybe this is not that much of an issue.

author: Faranight
author_rank: Unknown
timestamp: December 21, 2022, 01:44:29 pm
content: Keep in mind that 2A is a lot of current, especially, if you're going to be running that laser diode continuously for longer periods, so you're likely going to need a bigger battery. I'm assuming the diode already has sufficient cooling involved.I'm not sure, if driving a laser diode with PWM and then feeding it to a sensor is a good idea for sensor readings; it might interfere with your sensor and give you false readings? I don't know. You never said what kind of readings you need. But PWM generally means inconsistent (pulsed) light. Some sensors might not like that. Personally I'd just use a dedicated constant current driver IC, and that is assuming you don't need to dynamically adjust the brightness of the diode.You could always use multiple batteries in series with an appropriate buck converter. Is the battery detachable or is it built-in? If it's supposed to be detachable then you could use an existing external charger maybe?

author: semir-t
author_rank: Regular Contributor
timestamp: December 21, 2022, 02:11:25 pm
content: As you said, sensor would probably give false data because of the PWM so I am trying to avoid it.The laser diode will not work continuously, instead it will be turned on for few seconds while sensor captures the data and it will be turned off. This will be done periodically, and period will be configurable. (We can assume that in worst case scenario there will be pause between readings of 5-10 seconds).I need to have the capability to change the brightness of the laser led from 10%-80%. Heating part will be addressed. I am planning to have a larger copper are used for colling and also heat sink will be attached.Battery will be builtin. At this moment I will probably try to find 2S battery with 7.4V and find good buck converter for the driver.Thank you for your responses.

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2022, 05:19:22 pm
content: Quote from: Faranight on December 21, 2022, 07:47:10 amIf the battery voltage is not much higher than the LED voltage, then linear regulator efficiency is not that poor. Two lithium-ion cells in series would start at 8.2 volts yielding a worst case efficiency of 73% and it only gets better as the battery discharges.

author: MasterT
author_rank: Frequent Contributor
timestamp: December 21, 2022, 05:55:09 pm
content: 6V and 2.2 amps don;t line up, link to DS plz.Likely laser module has current limiting build-in , since 6V laser doesn't exist in nature, and 6V more like "nominal" voltage

author: ajb
author_rank: Super Contributor
timestamp: December 21, 2022, 08:56:21 pm
content: Since this is for a sensor, how stable do you need the output optical power to be? At ~14W input power you probably have at least 10W of heat to deal with, and the laser diode's efficiency has a negative temperature coefficient--so output power will drop as it heats up. If you need stable output power at significant power levels like this you generally need active cooling, and you need to take care with the thermal design to get that heat out of a small can package. You can also regulate the power output using a photodiode for feedback, but this of course complicates the driver design and has its own complications as far as accuracy and stability.Your simplest path forward would be to use a constant current boost converter. These are widely available for LEDs, just be aware that you need to be more careful about the output stability due to the higher sensitivity of the laser diode to being overdriven--even a brief overcurrent event can cause permanent physical damage to the laser due to the very high intracavity optical power density. Once the output or HR face of the die is damaged, the failure accelerates rapidly. This is a good reason to avoid PWM, as any overshoot on the rising edge results in a rapidly repeated stress on the diode. Instead, you can adjust the current setpoint of the driver. Some ICs have a control pin for this purpose, but you can also use a DAC and resistor network at the feedback node to do the adjustment.Quote from: MasterT on December 21, 2022, 05:55:09 pmNo, there are direct injection laser diodes with typical Vf specified as 6-7V and If at up to a couple amps. Blue and green diode lasers in particular can get into pretty high powers these days, I'm not sure about non-visible wavelengths. Datasheets for a lot of those are only available 'unofficially', though, depending on the target market for the specific laser diode.

author: semir-t
author_rank: Regular Contributor
timestamp: December 23, 2022, 07:31:40 am
content: I am aware of the issue with the laser getting very hot very fast so my design will try to address that but I will need to study this. Maybe Dave did some videos on it so I would need to investigate.Currently, I am tempted to go both ways:1. Get the 2S LiPo battery with 7.4V output voltage and with constant current buck converter (It looks like this one should be easier to find compared to the boost version). I would need to find different charging circuit then the one I am using now for 1S batteries.2. Use the 1S LiPO battery with 3.7V output voltage with constant current boost converter if I manage to find chip that can output 2A out current. I was searching for it but couldn't find any till now. Best that I have found is MIC2298 with the output current of 1A. If you have some suggestions feel free to share it.

author: MasterT
author_rank: Frequent Contributor
timestamp: December 23, 2022, 12:27:28 pm
content: Quote from: ajb on December 21, 2022, 08:56:21 pmThere are many fake news around us, data-sheets especially "unofficial" are no exception. Law of thermodynamics still in power, despite public opinion

author: jonpaul
author_rank: Super Contributor
timestamp: December 23, 2022, 01:24:23 pm
content: Beware of extreme eye hazardous situation of high power laser diodes.the laser diode needs a specialized driver, easiest is the off the shelf modules.Due to idiots attempts to use portable diode lasers as a weapon, eg shine beams at airliners cockpit or police, fire, Certain régions have prohibited import of high power (5mw) laser diodes especially hand held laser pointersIn Switzerland possession of a laser pointer or portable hand held laser is illegal.Check your country and région for legal and import restrictions.Finally the bare diodes may be very static sensitive and require a heatsink to meet Tjunct limitJon

author: semir-t
author_rank: Regular Contributor
timestamp: December 23, 2022, 03:51:57 pm
content: Do you have any part number for these Chinese modules?