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Thread: High Output Coherent Diode Lasers, I Need Some Help!

  1. #21
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    Heroic, I ment no disrespect, cabin fever and lack of employment are turning me into a world class grouch. Maxima Mea Culpa.

    Those diodes are a low ohms load, very sensitive to reverse voltage and spikes, in some cases they act like a short, in other cases almost a slightly negative resistance. He needs a good constant current source with a ramping startup , a clamp across the diode until the current is stable, and when he shuts down, or something starts to fail, he needs the clamp to engage. And fast. See www.lasorb.com for more details.

    I know, I know, the guys on youtube hook them to car batteries with a series resistor. One of the problems of being a so called professional is when I try stunts like that it blows up. Perhaps simply as one of God's little engineer jokes, if you don't know its wrong, it will work for you just fine.

    Steve




    Steve

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    Well, I must admit I had assumed that his Big-Ass Power Supply would have soft-start, which would make the sort of simple voltage limiter I suggested safe for the diode.

    In this situation I think I'd probably use a microcontroller to drive FETs into a big capacitor/inductor filter. This is the solution I've used when driving GaAs microwave amplifiers and they're about as fragile as anything you'll ever meet. If you use a micro like the Atmel ones you can drive the FETs directly from a PWM output and use one of the analog inputs as the feedback source; PCB tracks make good current measuring shunts at these currents, so you can control that too.

    All of this is a lot more involved than just voltage-limiting the thing

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    Quote Originally Posted by heroic View Post
    Well, I must admit I had assumed that his Big-Ass Power Supply would have soft-start, which would make the sort of simple voltage limiter I suggested safe for the diode.

    In this situation I think I'd probably use a microcontroller to drive FETs into a big capacitor/inductor filter. This is the solution I've used when driving GaAs microwave amplifiers and they're about as fragile as anything you'll ever meet. If you use a micro like the Atmel ones you can drive the FETs directly from a PWM output and use one of the analog inputs as the feedback source; PCB tracks make good current measuring shunts at these currents, so you can control that too.

    All of this is a lot more involved than just voltage-limiting the thing
    True. But it occured to me too, except I was thinking of a PWM controlled IGBT switched fast enough to filter smoothly then sense the current in a wire or track on a board. It's efficient, less waste, but those diodes really don't like transients so linear might be best. And a passbank can be made out of a load of very cheap transistors. But apparently IGBT's are cheap too now, and you'd maybe only need one of them, even for 150 amps... Maybe another one for the clamp Steve mentioned.


    Re that chiller, sure, looks like perfectly coherent logic to me too. And considering that beer chillers are so sought on eBay that prices go insane, I guess it's NOT a good idea to search on eBay. But find a closing down bar and you might get a good one for next to nothing. It's the kind of kit that gets left behind, usually.

  4. #24
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    The switcher is fine , if you filter the daylights out of it, Then usual scheme is a big P channel fet in series with the diode after the PSu for a soft start , thus blocking the conduction to the diode till something charges up, and then a relay as the clamp. So the current is already smooth and flowing before hiting the diode. BB details the reasons for the big, close in, relay at lasorb.com The usual scheme is the switcher watches the voltage across the linear passbank and keeps it at no more then say 9V to keep the linear dissapation down. If you keep the passbank voltage low enough , then you can use air cooled fets on a heatsink. If you keep the fet junction temps tracking each other, you can use many fets in parallel and analog gate drive. Other wise, get some 2n6259s or some other 250 watt brute force transistors in a to3 package. I don't reccomend 2n3055 , as they are poorly matched and have very low gain. You drive the passbank with the constant current feedback. dont omit the emitter resistors in the passbank, they force current sharing.
    for his purposes, hes best just starting with a water cooled passbank.

    Steve
    Last edited by mixedgas; 01-09-2009 at 18:55.

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    These have a fast bypass diode in them so reverse spikes are not a an issue, however If using a switch mode power supply + fets as a currenbt regulator it may ring and toast your diode, the Fets, or the power supplier. A good design will put a diode, a BIG capacitor, and a BIG current limiting resistor befor the FET regulator. Don't forget to put bypass diodes on the fets or you be popping 'em left and right! The fet regulator should be ran in PWM switch mode, be sure to put a choke w/ antispilke diode and a smaller after fet smoothing cap unless you want laser pulses at the max power as determined by your resistor. These diodes should still have a a small non electrolytic .2 to 5uF bypass cap across the leads to prevent spikes in any case. There is an internal anti-spike bypass diode inside the housing, but an external high current Schottky diode wouldn't hurt anything

    BTW: The Q&E version of the data sheet.

    WARNING! This laser diode emits potentially hazardous LASER energy when in operation! The beam that though infrared, may appear to be dim red because it is so powerful. DO NOT BE FOOLED; that same "weak" beam could easily light a cigarette for you! A single careless glance into the beam will cause instant blindness! Avoid direct exposure to the beam.

    Class IV LASER
    GaAlAs Simiconductor Diode LASER.
    WAVELENGTH: 805-810nm
    Max POWER: 100W

    Caution: Laser diodes are extremely static sensitive. A small discharge that cannot be felt can ruin it. It is critical that all work with bare laser diodes be done at a grounded and ESD controlled workstation. Carefully remove the diode from it's protective packaging ONLY when ready to use.

    The wiring is as follows:
    CASE OF LASER: LASER Positive +
    BOTH BIG LUGS: LASER Negative -

    To power this to test you need three C cell Ni-Cd batteries or any other source of CLEAN THREE to FIVE VOLTS maximum at a MINIMUM of 20 amps!. An old computer power supply's 3.3V or 5V rail will work, but in any case, you will need to make a custom high power low ohm resistor from nichrome heater wire to regulate the current. Though these aren't as static sensitive as a CD player laser, Do add a 10uF non-electrolytic capacitor across the leads and it will be ESD safe as long as you don't take your sparker to it. Operating current is 30A or more. The laser bar inside IS rated for use at up to 60 watts actual power so you should be able to source 70 amps through it, but make damn sure you got cold water flowing through it at a MINIMUM of 5 PSI and a MAXIMUM of 15 PSI!. For extended use soft water is recommended. There is no need to use distilled or deionized water. Do not look into the laser aperature as it WILL blind you instantly, and a direct reflection off something shiny such as a mirror or a lens will no doubt blind or cause severe eye damage as well! Getting laser protective eyewear for GaAlAs diode wavelength 700-900nm would be a very wise thing to do. Also do not look at the scattered light at close range or it will give you a bad headache from eyestrain as your eyes feel it as if you are looking at a 50W hallogen bulb at the same range.. Eye safe distance from the diffused light scattered off matte paper etc is about 4 feet for momentary exposure.

    THANK YOU

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    UPDATE:

    I now have a digital solid state cooler on the way made for one of these lasers. So, that should solve the temp issues. Does anyone know the specs of the thermistor on the head?

    I have a schematic for a PS I found on Sams laser FAQ for running one of these diodes.

    http://www.repairfaq.org/sam/sgdh1sch.pdf

    This should work. It fools the Vsense on the PS to think it's over voltage thus lowers the output voltage. I'm using nichrome wire as a power resistor instead of the copper wire spool Sam suggests. I'm also planning on using a 200A shunt with digital readout to measure the amps.

    I should have all the parts necessary to test in a week or so. I personally think this setup will work but is a little crude. I understand transistors, FET's, IGBT's and whatnot but have no clue how to properly implement them. If I had a schematic I could work off of that. If someone could offer me a schematic I could work off of to design a pass-bank type variable PS for one of these diodes, I'd be greatful!
    Thanks!
    Adam

  7. #27
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    Here is the text form this section on Sam's Laser FAQ...

    "
    Sam's High Power Laser Diode Driver 1 (SG-DH1)

    This isn't exactly an entire design but one that uses a common logic power supply in an unconventional way. It may be possible to use a high current switchmode power supply as a variable current laser diode driver as long as it has remote sensing capability. The remote sensing feedback loop maintains a constant voltage (the spec'd supply voltage) between RS+ and RS-. Normally, this is used to compensate for the voltage drop in the wiring harness. By applying a variable control voltage between RS+ and V+, the power supply can be fooled into producing any output voltage from near 0 to its maximum rating as long as its minimum load requirement is satisfied. With a small resistor in series with the laser diode (or for those willing to take risks, the resistance of the laser diode), this results in a variable current to the laser diode. The only limit on output current is the maximum rating of the power supply. These types of power supplies, capable of 50 A, 100 A, or even higher current, are readily available on the surplus market. However, this scheme may only work with certain models, those which power their control circuitry separately from the main output and don't go into some sort of undervoltage shutdown if the output voltage goes too low. I don't know how to determine which models satisfy this requirement.
    Vicor has application notes on doing this (among other things) with some of their Flatpac (among other) models. Search for "Programmable Current Source". The power supplies shown have an additional input called "Trim" which makes the modification particularly easy.
    I have not yet attempted to close the loop and provide actual current control but have opted for voltage control for now at least. The unit I've been using for these tests is a Shindengen PS5V100A, a fully enclosed fan cooled switchmode power supply that's about 15 years old. This unit is also nice in that it regulates well with no load. All that was needed was to remove the shorting link between V+ and RS+ and install a 20 ohm, 2 W resistor in its place. Then applying 0 to +15 VDC current limited by a 47 ohm, 5 W resistor across RS+ (+) and V+ (-), the output voltage would vary from near 0 to 5 VDC.

    Code:
    RS- <------ Remote Sense -------> RS+
            o                                 o
            |     V-  Vout   V+               |
            |     o          o                |
            |     |    R0    |          R1    |    R2
            |     |   250    |        20 2W   |  47 5W         Vcontrol
            +-----+---/\/\---+-----+---/\/\---+---/\/\---o + 0 to 15 VDC - o---+
            |                      |                                           |
            +---|<|---+---/\/\---+-+-------------------------------------------+
                LD1   |    R3    |
               Laser  | .05 500W |    Adjusting Vcontrol from 0 to 15 V varies
               Diode  o          o      Vout from 5 V to 0 V.
                     VS- Vsense VS+
    
     (R0 is internal to this particular power supply.)
    R3 can be constructed from a length of building wire. For example, 20 feet of #14 copper wire has a resistance of 0.05 ohms but water cooling would be needed if run near full current. I'm actually only using a head lamp load for testing and it works fine.
    The same scheme using RS- did not have enough range, probably due to the internal circuit design. This is too bad because the op-amp circuitry to drive it might have been simpler, or at least more intuitive to design.
    (I did try a test of the same approach with a Pioneer Magnetics dual output power supply (5 VDC at 59 A, 12 VDC at 67 A). While control was possible, it didn't behave nearly as perfectly as the Shindengen supply. More than 1/2 A of control current was required to change the 5 V output to 4 V. And while the 12 VDC output could be reduced to near 0 V, the cooling fans cut out at about 8 VDC so they would need to be powered separately for continuous operation at high current. But this might be nice for driving series connected laser diode bars.)
    The challenge is to convert this to a user friendly form that is safe for the laser diode. I am designing a control panel which incorporates what I hope will be fail-safe circuits to minimize the chance of excessive current either from power cycling or by user error. It will use closed loop feedback so the actual current can be set (rather than voltage) and includes a multifunction panel meter (set current, actual current, diode voltage). It will enable diode current only if all power supplies are stable and correct, the 10 turn current adjust pot is at 0, and with the press of a green button.
    However, initially, I'm using a 10 turn pot to control the current with a digital panel meter monitoring current via a 0.025 ohm sense resistor. Current is limited to between 50 A by a 0.06 ohm power resistor. Believe it or not, even 50 A is way below the limit for the diodes I need to test! See the section: Characteristics of Some Really High Power IR Diode Lasers.
    The schematic in Sam's High Power Laser Diode Driver 1 includes the control panel, connections to the 100 A power supply, and laser diode wiring.
    The basic control panel includes an Enable switch (eventually to be replaced with a keylock switch), Diode On and Off buttons, the 10 turn pot and DPM which reads 0 to 100 A. A differential amplifier converts the voltage across the current sense resistor into a DC voltage for the DPM. Without the differential amplifier, the control current was seriously affecting the readings as 1 A is only 2.5 mV. It's not possible (or at least not convenient) to separate the power and signal wiring to provide a proper single point ground.
    Both the sense and current limiting resistors are simply lengths of #14 copper wire with forced air cooling. This works very well with the diode's output digging pits in my brick beam stop. However, for continuous operation, it may be necessary to replace the #14 with #8 because even the modest heating of the copper changes its resistance enough to noticeably affect current.
    With minor changes in part values for the current limiting resistors, and the set-point for the power supply output voltage, it should be possible to drive a pair of laser diodes in series as long as they can be isolated from the common point. (The positive connection to a high power laser diode is usually the mounting block of the diode but it may not be connected to the external case itself.) However, one risk with this setup is that if one of the laser diodes fails shorted, it will likely take the other one as well since the current will spike to a very high level.
    The setup is shown in Photo of Sam's High Power Laser Diode Driver In Action. The water-cooled laser diode in the aluminum box is capable of 35 W output at around 55 to 60 A. The power supply is at the upper left with the control panel in front of it showing 40 A. Behind the power supply is the coil of white wire acting as a current limiting resistor next to its cooling fan. The current sense resistor is the 12 inches of so of red wire running from the power supply to the terminal strip. The blue-white glow is my digital camera's response to intense IR. The camera is really confused. When viewed through IR blocking laser goggles, a line on the brick starts glowing at a current of around 35 A and is white-hot at 45 A, where the current limit of the power supply is presently set (via the current limiting resistor and wiring resistance with the power supply adjusted for a maximum output of 5 VDC). The old darkroom enlarger timer in the upper right is used to turn the driver on for exactly the 20 seconds needed for my "meat thermometer" type power meter to take its reading, which would show about 23 W at 40 A for the diode in the photo. The reading at 45 A is about 27 W."
    Last edited by 300EVIL; 01-20-2009 at 16:33.

  8. #28
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    Quote Originally Posted by 300EVIL View Post
    UPDATE:

    I now have a digital solid state cooler on the way made for one of these lasers. So, that should solve the temp issues. Does anyone know the specs of the thermistor on the head?

    I have a schematic for a PS I found on Sams laser FAQ for running one of these diodes.

    http://www.repairfaq.org/sam/sgdh1sch.pdf

    This should work. It fools the Vsense on the PS to think it's over voltage thus lowers the output voltage. I'm using nichrome wire as a power resistor instead of the copper wire spool Sam suggests. I'm also planning on using a 200A shunt with digital readout to measure the amps.

    I should have all the parts necessary to test in a week or so. I personally think this setup will work but is a little crude. I understand transistors, FET's, IGBT's and whatnot but have no clue how to properly implement them. If I had a schematic I could work off of that. If someone could offer me a schematic I could work off of to design a pass-bank type variable PS for one of these diodes, I'd be greatful!
    Thanks!
    Adam
    What kind of digital solid state chiller?
    are more available?

  9. #29
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    Quote Originally Posted by 300EVIL View Post
    I'm using nichrome wire as a power resistor instead of the copper wire spool Sam suggests.
    I think Nichrome wire might change resistance more than copper, as there's less of it for a given resistance so more heat must leave from a given area. If you need it stable with temperature, the copper spool is better.

    Edit: That ASCII schematic, if you put CODE and /CODE at start and end, using square brackets for each tag, you'll get it rendered right.

  10. #30
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    Quote Originally Posted by The_Doctor View Post
    I think Nichrome wire might change resistance more than copper, as there's less of it for a given resistance so more heat must leave from a given area. If you need it stable with temperature, the copper spool is better.

    Edit: That ASCII schematic, if you put CODE and /CODE at start and end, using square brackets for each tag, you'll get it rendered right.
    My plan was to wrap the nichrome wire around a flat piece of mica to the correct resistance length and encase it in a cylinder filled with sand. Maybe I'll use clay and have it baked in a kiln. The reason I went with nichrome is because of the resistance per inch versus regular copper wire thus I can make the "homemade power resistor" more compact. If it doesn't work I'll just go with plain ol copper wire.

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