Laser diode driver help

[Laserz4sale]

Can someone draw up or give me a link of the schematics for a LT3080 Current regulator?
Thanks

 

[c4r0]

These's a current source schematic in the datasheet, page 17.

 

[HIMNL9]

For laser diodes, is better to stabilize it a bit more .....

I personally use this schematic, if the space is not a problem:

If you need to make it more small, just take away the ceramic capacitors (the 100nF ones are for better stability against self-oscillations, and the 1nF one is just for add a small soft-start ramp, but the module works also without them)

This schematic works until 1A without problems, and the maximum dropout of all the assembly is 1,5/1,6V around 700mA (total dropout).

Please note also that, if you need to parallel 2 of them for get more than 1A, they need to be LT3080-1, not LT3080 ..... the "-1" end means that they are directly parallelable, cause they already have a decoupling resistor inside ..... if you want to parallel 2 of the normal ones, you need to add decoupling resistors of at least 0,1 ohm on their outputs.

 

[3zuli]

Utfg, utfg...

 

[HIMNL9]

Utfg, utfg...

LOL, what ? (well, i hope it worth a "LOL", at least )

 

[Laserz4sale]

For laser diodes, is better to stabilize it a bit more .....

I personally use this schematic, if the space is not a problem:

If you need to make it more small, just take away the ceramic capacitors (the 100nF ones are for better stability against self-oscillations, and the 1nF one is just for add a small soft-start ramp, but the module works also without them)

This schematic works until 1A without problems, and the maximum dropout of all the assembly is 1,5/1,6V around 700mA (total dropout).

Please note also that, if you need to parallel 2 of them for get more than 1A, they need to be LT3080-1, not LT3080 ..... the "-1" end means that they are directly parallelable, cause they already have a decoupling resistor inside ..... if you want to parallel 2 of the normal ones, you need to add decoupling resistors of at least 0,1 ohm on their outputs.

Thanks. Did your Surface mount components arrive yet?
The LT3080 i saw was 8 pins... Not 3 so there are 2 inputs and i think 3 outputs, 1 NC , 1 Vcontrol and 1 Set. Which input do i use?

 

[HIMNL9]

No, components are not yet arrived, but i'm in Italy ..... Italian peoples are habitued to sssslllloooowwww postal system (our one is the world slowest in absolute ) ..... i let you know when they arrive.

About the LT3080, the 8 pins have the same functions, just the power input and the regulation input are separated, so if there's a power source that is more high of the power one, it can achieve a lower dropout ..... but for our use, this is not important ..... the corresponding pins for the 8 pins case are these ones:

pins 8, 7 and 5 tied together = IN

pin 4 = SET

pins 1, 2 and 3 tied together = OUT

pin 6 have no internal connection at all, can be connected to pins 5, 7 and 8 in a straight line for increase a bit the power dissipation and simplify the PCB design

pad pin (the large metal plate under the 8 pins case) - CAREFUL, this is NOT connected with ground, THIS IS INTERNALLY CONNECTED TO OUTPUT PINS ..... this is used for carry heat from the chip to any dissipation track, and MUST be paid attention that no other pins than OUT become connected to it ..... no need to connect to out pins, but MUST not be connected to any other pins, if not connected to out

 

[Laserz4sale]

So i short 8 with 7 with 5 and 1 with 2 with 3 right?

 

[HIMNL9]

Yes ..... if for simplicity you need to use a straight track, you can short also the pin 6 with 5, 7 and 8, nothing happens, cause the pin 6 is connected to nothing, internally ..... only, take care to not pass under the IC any track different from out, just for safety.

 

[Laserz4sale]

No, components are not yet arrived, but i'm in Italy ..... Italian peoples are habitued to sssslllloooowwww postal system (our one is the world slowest in absolute ) ..... i let you know when they arrive.

About the LT3080, the 8 pins have the same functions, just the power input and the regulation input are separated, so if there's a power source that is more high of the power one, it can achieve a lower dropout ..... but for our use, this is not important ..... the corresponding pins for the 8 pins case are these ones:

pins 8, 7 and 5 tied together = IN

pin 4 = SET

pins 1, 2 and 3 tied together = OUT

pin 6 have no internal connection at all, can be connected to pins 5, 7 and 8 in a straight line for increase a bit the power dissipation and simplify the PCB design

pad pin (the large metal plate under the 8 pins case) - CAREFUL, this is NOT connected with ground, THIS IS INTERNALLY CONNECTED TO OUTPUT PINS ..... this is used for carry heat from the chip to any dissipation track, and MUST be paid attention that no other pins than OUT become connected to it ..... no need to connect to out pins, but MUST not be connected to any other pins, if not connected to out

They sold out of the LT3080 so i bought a LM1086. can that use the same schematic as the LM317?

 

[HIMNL9]

Not sure, but i have some doubt that it can have the same stability, as current regulator ..... the LM317 have a different internal circuital configuration for the adjusting pin, so this can cause some differences in the working, and the different architecture can cause self-oscillations ..... if you want to try, i suggest you do do the tests with a dummy load, not directly with the laser diode.

 

[3zuli]

LOL, what ? (well, i hope it worth a "LOL", at least )

that was just a quick advice to Laserz4sale:na:

 

[Laserz4sale]

Not sure, but i have some doubt that it can have the same stability, as current regulator ..... the LM317 have a different internal circuital configuration for the adjusting pin, so this can cause some differences in the working, and the different architecture can cause self-oscillations ..... if you want to try, i suggest you do do the tests with a dummy load, not directly with the laser diode.

So that regulator wont work? So if i regulate the voltage to 3V, the maximum current going through will be 1.5A And that way won't work right?